<html><head><META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>ModSecurity® Reference Manual</title><link href="modsecurity-reference.css" rel="stylesheet" type="text/css"><meta content="DocBook XSL Stylesheets V1.69.1" name="generator"><link rel="start" href="#N10001" title="ModSecurity® Reference Manual"><link rel="next" href="#introduction" title="Introduction"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div style="background:#F5F5F5;width:100%;border-top:1px solid #DDDDDD;border-bottom:1px solid #DDDDDD"><table width="100%" cellspacing="0" cellpadding="0"><tr><td><a href="http://www.modsecurity.org"><img style="margin:4px" src="modsecurity.gif" width="120" height="36" alt="ModSecurity" border="0"></a></td><td align="right"><a href="http://www.breach.com"><img style="margin:6px" src="breach-logo-small.gif" height="36" width="100" border="0"></a></td></tr></table></div><div class="article" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="N10001"></a><span class="trademark">ModSecurity</span>® Reference Manual</h2></div><div><p class="releaseinfo">Version 2.5.12 (Feb 3, 2010)</p></div><div><p class="copyright">Copyright © 2004-2010 Breach Security, Inc. (<a href="http://www.breach.com" target="_top">http://www.breach.com</a>)</p></div></div><div></div><hr size="1"></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#introduction">Introduction</a></span></dt><dd><dl><dt><span class="section"><a href="#N1001D">HTTP Traffic Logging</a></span></dt><dt><span class="section"><a href="#N10022">Real-Time Monitoring and Attack Detection</a></span></dt><dt><span class="section"><a href="#N10027">Attack Prevention and Just-in-time Patching</a></span></dt><dt><span class="section"><a href="#N10038">Flexible Rule Engine</a></span></dt><dt><span class="section"><a href="#N1003D">Embedded-mode Deployment</a></span></dt><dt><span class="section"><a href="#N10054">Network-based Deployment</a></span></dt><dt><span class="section"><a href="#N10059">Portability</a></span></dt><dt><span class="section"><a href="#licensing">Licensing</a></span></dt></dl></dd><dt><span class="section"><a href="#N10067"><span class="trademark">ModSecurity Core Rules</span>™</a></span></dt><dd><dl><dt><span class="section"><a href="#N1006C">Overview</a></span></dt><dt><span class="section"><a href="#N10075">Core Rules Content</a></span></dt></dl></dd><dt><span class="section"><a href="#installation">Installation</a></span></dt><dt><span class="section"><a href="#configuration-directives">Configuration Directives</a></span></dt><dd><dl><dt><span class="section"><a href="#N101B0"><code class="literal">SecAction</code></a></span></dt><dt><span class="section"><a href="#N101E1"><code class="literal">SecArgumentSeparator</code></a></span></dt><dt><span class="section"><a href="#N10216"><code class="literal">SecAuditEngine</code></a></span></dt><dt><span class="section"><a href="#N10263"><code class="literal">SecAuditLog</code></a></span></dt><dt><span class="section"><a href="#N10293"><code class="literal">SecAuditLog2</code></a></span></dt><dt><span class="section"><a href="#N102C5"><code class="literal">SecAuditLogDirMode</code></a></span></dt><dt><span class="section"><a href="#N102F3"><code class="literal">SecAuditLogFileMode</code></a></span></dt><dt><span class="section"><a href="#N10321"><code class="literal">SecAuditLogParts</code></a></span></dt><dt><span class="section"><a href="#N103B4"><code class="literal">SecAuditLogRelevantStatus</code></a></span></dt><dt><span class="section"><a href="#N103E5"><code class="literal">SecAuditLogStorageDir</code></a></span></dt><dt><span class="section"><a href="#N1040E"><code class="literal">SecAuditLogType</code></a></span></dt><dt><span class="section"><a href="#N1044A"><code class="literal">SecCacheTransformations</code> (Deprecated/Experimental)</a></span></dt><dt><span class="section"><a href="#N1049C"><code class="literal">SecChrootDir</code></a></span></dt><dt><span class="section"><a href="#N104DD"><code class="literal">SecComponentSignature</code></a></span></dt><dt><span class="section"><a href="#N10504"><code class="literal">SecContentInjection</code></a></span></dt><dt><span class="section"><a href="#N10533"><code class="literal">SecCookieFormat</code></a></span></dt><dt><span class="section"><a href="#N10569"><code class="literal">SecDataDir</code></a></span></dt><dt><span class="section"><a href="#N1058C"><code class="literal">SecDebugLog</code></a></span></dt><dt><span class="section"><a href="#N105B3"><code class="literal">SecDebugLogLevel</code></a></span></dt><dt><span class="section"><a href="#N10613"><code class="literal">SecDefaultAction</code></a></span></dt><dt><span class="section"><a href="#N1065E"><code class="literal">SecGeoLookupDb</code></a></span></dt><dt><span class="section"><a href="#N10689"><code class="literal">SecGuardianLog</code></a></span></dt><dt><span class="section"><a href="#N106BC"><code class="literal">SecMarker</code></a></span></dt><dt><span class="section"><a href="#N106F4"><code class="literal">SecPcreMatchLimit</code></a></span></dt><dt><span class="section"><a href="#N10725"><code class="literal">SecPcreMatchLimitRecursion</code></a></span></dt><dt><span class="section"><a href="#N10756"><code class="literal">SecPdfProtect</code></a></span></dt><dt><span class="section"><a href="#N10781"><code class="literal">SecPdfProtectMethod</code></a></span></dt><dt><span class="section"><a href="#N107B7"><code class="literal">SecPdfProtectSecret</code></a></span></dt><dt><span class="section"><a href="#N107DE"><code class="literal">SecPdfProtectTimeout</code></a></span></dt><dt><span class="section"><a href="#N1080C"><code class="literal">SecPdfProtectTokenName</code></a></span></dt><dt><span class="section"><a href="#N1083A"><code class="literal">SecRequestBodyAccess</code></a></span></dt><dt><span class="section"><a href="#N10878"><code class="literal">SecRequestBodyLimit</code></a></span></dt><dt><span class="section"><a href="#N1089B"><code class="literal">SecRequestBodyNoFilesLimit</code></a></span></dt><dt><span class="section"><a href="#N108C6"><code class="literal">SecRequestBodyInMemoryLimit</code></a></span></dt><dt><span class="section"><a href="#N108F2"><code class="literal">SecResponseBodyLimit</code></a></span></dt><dt><span class="section"><a href="#N1091E"><code class="literal">SecResponseBodyLimitAction</code></a></span></dt><dt><span class="section"><a href="#N10949"><code class="literal">SecResponseBodyMimeType</code></a></span></dt><dt><span class="section"><a href="#N10985"><code class="literal">SecResponseBodyMimeTypesClear</code></a></span></dt><dt><span class="section"><a href="#N109B0"><code class="literal">SecResponseBodyAccess</code></a></span></dt><dt><span class="section"><a href="#N109E6"><code class="literal">SecRule</code></a></span></dt><dt><span class="section"><a href="#N10AD6"><code class="literal">SecRuleInheritance</code></a></span></dt><dt><span class="section"><a href="#N10B39"><code class="literal">SecRuleEngine</code></a></span></dt><dt><span class="section"><a href="#N10B75"><code class="literal">SecRuleRemoveById</code></a></span></dt><dt><span class="section"><a href="#N10B9F"><code class="literal">SecRuleRemoveByMsg</code></a></span></dt><dt><span class="section"><a href="#N10BCA"><code class="literal">SecRuleScript</code> (Experimental)</a></span></dt><dt><span class="section"><a href="#N10C24"><code class="literal">SecRuleUpdateActionById</code></a></span></dt><dt><span class="section"><a href="#N10C53"><code class="literal">SecServerSignature</code></a></span></dt><dt><span class="section"><a href="#N10C7A"><code class="literal">SecTmpDir</code></a></span></dt><dt><span class="section"><a href="#N10CA1"><code class="literal">SecUploadDir</code></a></span></dt><dt><span class="section"><a href="#N10CD0"><code class="literal">SecUploadFileLimit</code></a></span></dt><dt><span class="section"><a href="#N10D12"><code class="literal">SecUploadFileMode</code></a></span></dt><dt><span class="section"><a href="#N10D3C"><code class="literal">SecUploadKeepFiles</code></a></span></dt><dt><span class="section"><a href="#N10D7C"><code class="literal">SecWebAppId</code></a></span></dt></dl></dd><dt><span class="section"><a href="#processing-phases">Processing Phases</a></span></dt><dd><dl><dt><span class="section"><a href="#N10E17">Phase Request Headers</a></span></dt><dt><span class="section"><a href="#N10E21">Phase Request Body</a></span></dt><dt><span class="section"><a href="#N10E3B">Phase Response Headers</a></span></dt><dt><span class="section"><a href="#N10E40">Phase Response Body</a></span></dt><dt><span class="section"><a href="#N10E45">Phase Logging</a></span></dt></dl></dd><dt><span class="section"><a href="#variables">Variables</a></span></dt><dd><dl><dt><span class="section"><a href="#N10E50"><code class="literal">ARGS</code></a></span></dt><dt><span class="section"><a href="#N10EA2"><code class="literal">ARGS_COMBINED_SIZE</code></a></span></dt><dt><span class="section"><a href="#N10EAF"><code class="literal">ARGS_NAMES</code></a></span></dt><dt><span class="section"><a href="#N10EBC"><code class="literal">ARGS_GET</code></a></span></dt><dt><span class="section"><a href="#N10ECA"><code class="literal">ARGS_GET_NAMES</code></a></span></dt><dt><span class="section"><a href="#N10ED8"><code class="literal">ARGS_POST</code></a></span></dt><dt><span class="section"><a href="#N10EE6"><code class="literal">ARGS_POST_NAMES</code></a></span></dt><dt><span class="section"><a href="#N10EF4"><code class="literal">AUTH_TYPE</code></a></span></dt><dt><span class="section"><a href="#N10F0A"><code class="literal">ENV</code></a></span></dt><dt><span class="section"><a href="#N10F1E"><code class="literal">FILES</code></a></span></dt><dt><span class="section"><a href="#N10F2B"><code class="literal">FILES_COMBINED_SIZE</code></a></span></dt><dt><span class="section"><a href="#N10F38"><code class="literal">FILES_NAMES</code></a></span></dt><dt><span class="section"><a href="#N10F45"><code class="literal">FILES_SIZES</code></a></span></dt><dt><span class="section"><a href="#N10F52"><code class="literal">FILES_TMPNAMES</code></a></span></dt><dt><span class="section"><a href="#N10F63"><code class="literal">GEO</code></a></span></dt><dt><span class="section"><a href="#N10FB5"><code class="literal">HIGHEST_SEVERITY</code></a></span></dt><dt><span class="section"><a href="#N10FC8"><code class="literal">MATCHED_VAR</code></a></span></dt><dt><span class="section"><a href="#N10FD9"><code class="literal">MATCHED_VAR_NAME</code></a></span></dt><dt><span class="section"><a href="#N10FE6"><code class="literal">MODSEC_BUILD</code></a></span></dt><dt><span class="section"><a href="#N10FF3"><code class="literal">MULTIPART_CRLF_LF_LINES</code></a></span></dt><dt><span class="section"><a href="#N1101E"><code class="literal">MULTIPART_STRICT_ERROR</code></a></span></dt><dt><span class="section"><a href="#N11072"><code class="literal">MULTIPART_UNMATCHED_BOUNDARY</code></a></span></dt><dt><span class="section"><a href="#N11088"><code class="literal">PATH_INFO</code></a></span></dt><dt><span class="section"><a href="#N11095"><code class="literal">QUERY_STRING</code></a></span></dt><dt><span class="section"><a href="#N110A2"><code class="literal">REMOTE_ADDR</code></a></span></dt><dt><span class="section"><a href="#N110AF"><code class="literal">REMOTE_HOST</code></a></span></dt><dt><span class="section"><a href="#N110BC"><code class="literal">REMOTE_PORT</code></a></span></dt><dt><span class="section"><a href="#N110CD"><code class="literal">REMOTE_USER</code></a></span></dt><dt><span class="section"><a href="#N110DF"><code class="literal">REQBODY_PROCESSOR</code></a></span></dt><dt><span class="section"><a href="#N110F8"><code class="literal">REQBODY_PROCESSOR_ERROR</code></a></span></dt><dt><span class="section"><a href="#N11110"><code class="literal">REQBODY_PROCESSOR_ERROR_MSG</code></a></span></dt><dt><span class="section"><a href="#N1111D"><code class="literal">REQUEST_BASENAME</code></a></span></dt><dt><span class="section"><a href="#N1113F"><code class="literal">REQUEST_BODY</code></a></span></dt><dt><span class="section"><a href="#N11173"><code class="literal">REQUEST_COOKIES</code></a></span></dt><dt><span class="section"><a href="#N11180"><code class="literal">REQUEST_COOKIES_NAMES</code></a></span></dt><dt><span class="section"><a href="#N1118D"><code class="literal">REQUEST_FILENAME</code></a></span></dt><dt><span class="section"><a href="#N111A9"><code class="literal">REQUEST_HEADERS</code></a></span></dt><dt><span class="section"><a href="#N111CD"><code class="literal">REQUEST_HEADERS_NAMES</code></a></span></dt><dt><span class="section"><a href="#N111DA"><code class="literal">REQUEST_LINE</code></a></span></dt><dt><span class="section"><a href="#N111E7"><code class="literal">REQUEST_METHOD</code></a></span></dt><dt><span class="section"><a href="#N111FA"><code class="literal">REQUEST_PROTOCOL</code></a></span></dt><dt><span class="section"><a href="#N11207"><code class="literal">REQUEST_URI</code></a></span></dt><dt><span class="section"><a href="#N11225"><code class="literal">REQUEST_URI_RAW</code></a></span></dt><dt><span class="section"><a href="#N1123F"><code class="literal">RESPONSE_BODY</code></a></span></dt><dt><span class="section"><a href="#N1124E"><code class="literal">RESPONSE_CONTENT_LENGTH</code></a></span></dt><dt><span class="section"><a href="#N1125F"><code class="literal">RESPONSE_CONTENT_TYPE</code></a></span></dt><dt><span class="section"><a href="#N11266"><code class="literal">RESPONSE_HEADERS</code></a></span></dt><dt><span class="section"><a href="#N1127A"><code class="literal">RESPONSE_HEADERS_NAMES</code></a></span></dt><dt><span class="section"><a href="#N1128C"><code class="literal">RESPONSE_PROTOCOL</code></a></span></dt><dt><span class="section"><a href="#N11299"><code class="literal">RESPONSE_STATUS</code></a></span></dt><dt><span class="section"><a href="#N112AB"><code class="literal">RULE</code></a></span></dt><dt><span class="section"><a href="#N112D0"><code class="literal">SCRIPT_BASENAME</code></a></span></dt><dt><span class="section"><a href="#N112E2"><code class="literal">SCRIPT_FILENAME</code></a></span></dt><dt><span class="section"><a href="#N112F4"><code class="literal">SCRIPT_GID</code></a></span></dt><dt><span class="section"><a href="#N11306"><code class="literal">SCRIPT_GROUPNAME</code></a></span></dt><dt><span class="section"><a href="#N11318"><code class="literal">SCRIPT_MODE</code></a></span></dt><dt><span class="section"><a href="#N1132A"><code class="literal">SCRIPT_UID</code></a></span></dt><dt><span class="section"><a href="#N1133C"><code class="literal">SCRIPT_USERNAME</code></a></span></dt><dt><span class="section"><a href="#N1134E"><code class="literal">SERVER_ADDR</code></a></span></dt><dt><span class="section"><a href="#N1135B"><code class="literal">SERVER_NAME</code></a></span></dt><dt><span class="section"><a href="#N1136D"><code class="literal">SERVER_PORT</code></a></span></dt><dt><span class="section"><a href="#N1137A"><code class="literal">SESSION</code></a></span></dt><dt><span class="section"><a href="#N11394"><code class="literal">SESSIONID</code></a></span></dt><dt><span class="section"><a href="#N113A5"><code class="literal">TIME</code></a></span></dt><dt><span class="section"><a href="#N113B2"><code class="literal">TIME_DAY</code></a></span></dt><dt><span class="section"><a href="#N113BF"><code class="literal">TIME_EPOCH</code></a></span></dt><dt><span class="section"><a href="#N113CC"><code class="literal">TIME_HOUR</code></a></span></dt><dt><span class="section"><a href="#N113D9"><code class="literal">TIME_MIN</code></a></span></dt><dt><span class="section"><a href="#N113E6"><code class="literal">TIME_MON</code></a></span></dt><dt><span class="section"><a href="#N113F3"><code class="literal">TIME_SEC</code></a></span></dt><dt><span class="section"><a href="#N11400"><code class="literal">TIME_WDAY</code></a></span></dt><dt><span class="section"><a href="#N1140D"><code class="literal">TIME_YEAR</code></a></span></dt><dt><span class="section"><a href="#N1141A"><code class="literal">TX</code></a></span></dt><dt><span class="section"><a href="#N11462"><code class="literal">USERID</code></a></span></dt><dt><span class="section"><a href="#N11473"><code class="literal">WEBAPPID</code></a></span></dt><dt><span class="section"><a href="#N11484"><code class="literal">WEBSERVER_ERROR_LOG</code></a></span></dt><dt><span class="section"><a href="#N11491"><code class="literal">XML</code></a></span></dt></dl></dd><dt><span class="section"><a href="#transformation-functions">Transformation functions</a></span></dt><dd><dl><dt><span class="section"><a href="#N114EE"><code class="literal">base64Decode</code></a></span></dt><dt><span class="section"><a href="#N114F5"><code class="literal">base64Encode</code></a></span></dt><dt><span class="section"><a href="#N114FC"><code class="literal">compressWhitespace</code></a></span></dt><dt><span class="section"><a href="#N11503">cssDecode</a></span></dt><dt><span class="section"><a href="#N11514"><code class="literal">escapeSeqDecode</code></a></span></dt><dt><span class="section"><a href="#N1154F"><code class="literal">hexDecode</code></a></span></dt><dt><span class="section"><a href="#N11556"><code class="literal">hexEncode</code></a></span></dt><dt><span class="section"><a href="#N1155D"><code class="literal">htmlEntityDecode</code></a></span></dt><dt><span class="section"><a href="#N1159F"><code class="literal">jsDecode</code></a></span></dt><dt><span class="section"><a href="#N115B2"><code class="literal">length</code></a></span></dt><dt><span class="section"><a href="#N115B9"><code class="literal">lowercase</code></a></span></dt><dt><span class="section"><a href="#N115C0"><code class="literal">md5</code></a></span></dt><dt><span class="section"><a href="#N115CB"><code class="literal"><code class="literal">none</code></code></a></span></dt><dt><span class="section"><a href="#N115D4"><code class="literal">normalisePath</code></a></span></dt><dt><span class="section"><a href="#N115DB"><code class="literal">normalisePathWin</code></a></span></dt><dt><span class="section"><a href="#N115E6"><code class="literal">parityEven7bit</code></a></span></dt><dt><span class="section"><a href="#N115ED"><code class="literal">parityOdd7bit</code></a></span></dt><dt><span class="section"><a href="#N115F4"><code class="literal">parityZero7bit</code></a></span></dt><dt><span class="section"><a href="#N115FB"><code class="literal">removeNulls</code></a></span></dt><dt><span class="section"><a href="#N11602"><code class="literal">removeWhitespace</code></a></span></dt><dt><span class="section"><a href="#N11609"><code class="literal">replaceComments</code></a></span></dt><dt><span class="section"><a href="#N11618"><code class="literal">replaceNulls</code></a></span></dt><dt><span class="section"><a href="#N1161F"><code class="literal">urlDecode</code></a></span></dt><dt><span class="section"><a href="#N1162A"><code class="literal">urlDecodeUni</code></a></span></dt><dt><span class="section"><a href="#N11645"><code class="literal">urlEncode</code></a></span></dt><dt><span class="section"><a href="#N1164C"><code class="literal">sha1</code></a></span></dt><dt><span class="section"><a href="#N11657"><code class="literal">trimLeft</code></a></span></dt><dt><span class="section"><a href="#N1165E"><code class="literal">trimRight</code></a></span></dt><dt><span class="section"><a href="#N11665"><code class="literal">trim</code></a></span></dt></dl></dd><dt><span class="section"><a href="#actions">Actions</a></span></dt><dd><dl><dt><span class="section"><a href="#N116AD"><code class="literal">allow</code></a></span></dt><dt><span class="section"><a href="#N116FD">append</a></span></dt><dt><span class="section"><a href="#N1171F"><code class="literal">auditlog</code></a></span></dt><dt><span class="section"><a href="#N11739"><code class="literal">block</code></a></span></dt><dt><span class="section"><a href="#N1177E"><code class="literal">capture</code></a></span></dt><dt><span class="section"><a href="#N11798"><code class="literal">chain</code></a></span></dt><dt><span class="section"><a href="#N117B3"><code class="literal">ctl</code></a></span></dt><dt><span class="section"><a href="#N11847"><code class="literal">deny</code></a></span></dt><dt><span class="section"><a href="#N1185C"><code class="literal">deprecatevar</code></a></span></dt><dt><span class="section"><a href="#N11873"><code class="literal">drop</code></a></span></dt><dt><span class="section"><a href="#N1188D"><code class="literal">exec</code></a></span></dt><dt><span class="section"><a href="#N118B6"><code class="literal">expirevar</code></a></span></dt><dt><span class="section"><a href="#N118D0"><code class="literal">id</code></a></span></dt><dt><span class="section"><a href="#N11912"><code class="literal">initcol</code></a></span></dt><dt><span class="section"><a href="#N11939"><code class="literal">log</code></a></span></dt><dt><span class="section"><a href="#N11952"><code class="literal">logdata</code></a></span></dt><dt><span class="section"><a href="#N1196B"><code class="literal">msg</code></a></span></dt><dt><span class="section"><a href="#N11987"><code class="literal">multiMatch</code></a></span></dt><dt><span class="section"><a href="#N119A0"><code class="literal">noauditlog</code></a></span></dt><dt><span class="section"><a href="#N119BD"><code class="literal">nolog</code></a></span></dt><dt><span class="section"><a href="#N119D6"><code class="literal">pass</code></a></span></dt><dt><span class="section"><a href="#N11A05"><code class="literal">pause</code></a></span></dt><dt><span class="section"><a href="#N11A1E"><code class="literal">phase</code></a></span></dt><dt><span class="section"><a href="#N11A38">prepend</a></span></dt><dt><span class="section"><a href="#N11A5A"><code class="literal">proxy</code></a></span></dt><dt><span class="section"><a href="#N11A73"><code class="literal">redirect</code></a></span></dt><dt><span class="section"><a href="#N11A90"><code class="literal">rev</code></a></span></dt><dt><span class="section"><a href="#N11AAE"><code class="literal">sanitiseArg</code></a></span></dt><dt><span class="section"><a href="#N11AC7"><code class="literal">sanitiseMatched</code></a></span></dt><dt><span class="section"><a href="#N11AE3"><code class="literal">sanitiseRequestHeader</code></a></span></dt><dt><span class="section"><a href="#N11AFC"><code class="literal">sanitiseResponseHeader</code></a></span></dt><dt><span class="section"><a href="#N11B15"><code class="literal">severity</code></a></span></dt><dt><span class="section"><a href="#N11B4A"><code class="literal">setuid</code></a></span></dt><dt><span class="section"><a href="#N11B6C"><code class="literal">setsid</code></a></span></dt><dt><span class="section"><a href="#N11B91"><code class="literal">setenv</code></a></span></dt><dt><span class="section"><a href="#N11BB3"><code class="literal">setvar</code></a></span></dt><dt><span class="section"><a href="#N11BD9"><code class="literal">skip</code></a></span></dt><dt><span class="section"><a href="#N11BF4"><code class="literal">skipAfter</code></a></span></dt><dt><span class="section"><a href="#N11C16"><code class="literal">status</code></a></span></dt><dt><span class="section"><a href="#N11C38"><code class="literal">t</code></a></span></dt><dt><span class="section"><a href="#N11C51"><code class="literal">tag</code></a></span></dt><dt><span class="section"><a href="#N11C6B"><code class="literal">xmlns</code></a></span></dt></dl></dd><dt><span class="section"><a href="#operators">Operators</a></span></dt><dd><dl><dt><span class="section"><a href="#N11C8A"><code class="literal">beginsWith</code></a></span></dt><dt><span class="section"><a href="#N11CA2"><code class="literal">contains</code></a></span></dt><dt><span class="section"><a href="#N11CB6"><code class="literal">endsWith</code></a></span></dt><dt><span class="section"><a href="#N11CCA"><code class="literal">eq</code></a></span></dt><dt><span class="section"><a href="#N11CE1"><code class="literal">ge</code></a></span></dt><dt><span class="section"><a href="#N11CF8"><code class="literal">geoLookup</code></a></span></dt><dt><span class="section"><a href="#N11D21"><code class="literal">gt</code></a></span></dt><dt><span class="section"><a href="#N11D38"><code class="literal">inspectFile</code></a></span></dt><dt><span class="section"><a href="#N11D5A"><code class="literal">le</code></a></span></dt><dt><span class="section"><a href="#N11D71"><code class="literal">lt</code></a></span></dt><dt><span class="section"><a href="#N11D88"><code class="literal">pm</code></a></span></dt><dt><span class="section"><a href="#N11D9B"><code class="literal">pmFromFile</code></a></span></dt><dt><span class="section"><a href="#N11DCA"><code class="literal">rbl</code></a></span></dt><dt><span class="section"><a href="#N11DDB"><code class="literal">rx</code></a></span></dt><dt><span class="section"><a href="#N11E15"><code class="literal">streq</code></a></span></dt><dt><span class="section"><a href="#N11E29"><code class="literal">validateByteRange</code></a></span></dt><dt><span class="section"><a href="#N11E4F"><code class="literal">validateDTD</code></a></span></dt><dt><span class="section"><a href="#N11E63"><code class="literal">validateSchema</code></a></span></dt><dt><span class="section"><a href="#N11E77"><code class="literal">validateUrlEncoding</code></a></span></dt><dt><span class="section"><a href="#N11E91"><code class="literal">validateUtf8Encoding</code></a></span></dt><dt><span class="section"><a href="#N11EB3"><code class="literal">verifyCC</code></a></span></dt><dt><span class="section"><a href="#N11EC4"><code class="literal">within</code></a></span></dt></dl></dd><dt><span class="section"><a href="#N11EDC">Macro Expansion</a></span></dt><dt><span class="section"><a href="#N11EEA">Persistant Storage</a></span></dt><dt><span class="section"><a href="#N11F4E">Miscellaneous Topics</a></span></dt><dd><dl><dt><span class="section"><a href="#N11F52">Impedance Mismatch</a></span></dt></dl></dd></dl></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="introduction"></a>Introduction</h2></div></div><div></div></div><p>ModSecurity is a web application firewall (WAF). With over 70% of attacks now carried out over the web application level, organisations need all the help they can get in making their systems secure. WAFs are deployed to establish an increased external security layer to detect and/or prevent attacks before they reach web applications. ModSecurity provides protection from a range of attacks against web applications and allows for HTTP traffic monitoring and real-time analysis with little or no changes to existing infrastructure.</p><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1001D"></a>HTTP Traffic Logging</h3></div></div><div></div></div><p>Web servers are typically well-equipped to log traffic in a form useful for marketing analyses, but fall short logging traffic to web applications. In particular, most are not capable of logging the request bodies. Your adversaries know this, and that is why most attacks are now carried out via POST requests, rendering your systems blind. ModSecurity makes full HTTP transaction logging possible, allowing complete requests and responses to be logged. Its logging facilities also allow fine-grained decisions to be made about exactly what is logged and when, ensuring only the relevant data is recorded. As some of the request and/or response may contain sensitive data in certain fields, ModSecurity can be configured to mask these fields before they are written to the audit log.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10022"></a>Real-Time Monitoring and Attack Detection</h3></div></div><div></div></div><p>In addition to providing logging facilities, ModSecurity can monitor the HTTP traffic in real time in order to detect attacks. In this case, ModSecurity operates as a web intrusion detection tool, allowing you to react to suspicious events that take place at your web systems.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10027"></a>Attack Prevention and Just-in-time Patching</h3></div></div><div></div></div><p>ModSecurity can also act immediately to prevent attacks from reaching your web applications. There are three commonly used approaches:</p><div class="orderedlist"><ol type="1"><li><p>Negative security model. A negative security model monitors requests for anomalies, unusual behaviour, and common web application attacks. It keeps anomaly scores for each request, IP addresses, application sessions, and user accounts. Requests with high anomaly scores are either logged or rejected altogether.</p></li><li><p>Positive security model. When a positive security model is deployed, only requests that are known to be valid are accepted, with everything else rejected. This model requires knownledge of the web applications you are protecting. Therefore a positive security model works best with applications that are heavily used but rarely updated so that maintenance of the model is minimized.</p></li><li><p>Known weaknesses and vulnerabilities. Its rule language makes ModSecurity an ideal external patching tool. External patching (sometimes referred to as Virtual Patching) is about reducing the window of opportunity. Time needed to patch application vulnerabilities often runs to weeks in many organisations. With ModSecurity, applications can be patched from the outside, without touching the application source code (and even without any access to it), making your systems secure until a proper patch is applied to the application.</p></li></ol></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10038"></a>Flexible Rule Engine</h3></div></div><div></div></div><p>A flexible rule engine sits in the heart of ModSecurity. It implements the ModSecurity Rule Language, which is a specialised programming language designed to work with HTTP transaction data. The ModSecurity Rule Language is designed to be easy to use, yet flexible: common operations are simple while complex operations are possible. Certified ModSecurity Rules, included with ModSecurity, contain a comprehensive set of rules that implement general-purpose hardening, protocol validation and detection of common web application security issues. Heavily commented, these rules can be used as a learning tool.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1003D"></a>Embedded-mode Deployment</h3></div></div><div></div></div><p>ModSecurity is an embeddable web application firewall, which means it can be deployed as part of your existing web server infrastructure provided your web servers are Apache-based. This deployment method has certain advantages:</p><div class="orderedlist"><ol type="1"><li><p>No changes to existing network. It only takes a few minutes to add ModSecurity to your existing web servers. And because it was designed to be completely passive by default, you are free to deploy it incrementally and only use the features you need. It is equally easy to remove or deactivate it if required.</p></li><li><p>No single point of failure. Unlike with network-based deployments, you will not be introducing a new point of failure to your system.</p></li><li><p>Implicit load balancing and scaling. Because it works embedded in web servers, ModSecurity will automatically take advantage of the additional load balancing and scalability features. You will not need to think of load balancing and scaling unless your existing system needs them.</p></li><li><p>Minimal overhead. Because it works from inside the web server process there is no overhead for network communication and minimal overhead in parsing and data exchange.</p></li><li><p>No problem with encrypted or compressed content. Many IDS systems have difficulties analysing SSL traffic. This is not a problem for ModSecurity because it is positioned to work when the traffic is decrypted and decompressed.</p></li></ol></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10054"></a>Network-based Deployment</h3></div></div><div></div></div><p>ModSecurity works equally well when deployed as part of an Apache-based reverse proxy server, and many of our customers choose to do so. In this scenario, one installation of ModSecurity can protect any number of web servers (even the non-Apache ones).</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10059"></a>Portability</h3></div></div><div></div></div><p>ModSecurity is known to work well on a wide range of operating systems. Our customers are successfully running it on Linux, Windows, Solaris, FreeBSD, OpenBSD, NetBSD, AIX, Mac OS X, and HP-UX.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="licensing"></a>Licensing</h3></div></div><div></div></div><p>ModSecurity is available under two licenses. Users can choose to use the software under the terms of the GNU General Public License version 2 (licence text is included with the distribution), as an Open Source / Free Software product. A range of commercial licenses is also available, together with a range of commercial support contracts. For more information on commercial licensing please contact Breach Security.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>ModSecurity, mod_security, ModSecurity Pro, and ModSecurity Core Rules are trademarks or registered trademarks of Breach Security, Inc.</p></div></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="N10067"></a><span class="trademark">ModSecurity Core Rules</span>™</h2></div></div><div></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1006C"></a>Overview</h3></div></div><div></div></div><p>ModSecurity is a web application firewall engine that provides very little protection on its own. In order to become useful, ModSecurity must be configured with rules. In order to enable users to take full advantage of ModSecurity out of the box, Breach Security, Inc. is providing a free certified rule set for ModSecurity 2.x. Unlike intrusion detection and prevention systems, which rely on signatures specific to known vulnerabilities, the Core Rules provide generic protection from unknown vulnerabilities often found in web applications, which are in most cases custom coded. The Core Rules are heavily commented to allow it to be used as a step-by-step deployment guide for ModSecurity. The latest Core Rules can be found at the ModSecurity website - <a href="http://www.modsecurity.org/projects/rules/" target="_top">http://www.modsecurity.org/projects/rules/</a>.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10075"></a>Core Rules Content</h3></div></div><div></div></div><p>In order to provide generic web applications protection, the Core Rules use the following techniques:</p><div class="itemizedlist"><ul type="disc"><li><p>HTTP protection - detecting violations of the HTTP protocol and a locally defined usage policy.</p></li><li><p>Common Web Attacks Protection - detecting common web application security attack.</p></li><li><p>Automation detection - Detecting bots, crawlers, scanners and other surface malicious activity.</p></li><li><p>Trojan Protection - Detecting access to Trojans horses.</p></li><li><p>Error Hiding - Disguising error messages sent by the server.</p></li></ul></div></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="installation"></a>Installation</h2></div></div><div></div></div><p>ModSecurity installation requirements:</p><div class="orderedlist"><ol type="1"><li><p>ModSecurity 2.x works only with Apache 2.0.x or higher. Version 2.2.x is highly recommended.</p></li><li><p>Make sure you have <code class="literal">mod_unique_id</code> installed.</p><p>mod_unique_id is packaged with Apache httpd.</p></li><li><p>libapr and libapr-util</p><p><a href="http://apr.apache.org/" target="_top">http://apr.apache.org/</a></p></li><li><p>libpcre</p><p><a href="http://www.pcre.org/" target="_top">http://www.pcre.org/</a></p></li><li><p>libxml2</p><p><a href="http://xmlsoft.org/downloads.html" target="_top">http://xmlsoft.org/downloads.html</a></p></li><li><p>liblua v5.1.x</p><p>This library is optional and only needed if you will be using the new Lua engine.</p><p><a href="http://www.lua.org/download.html" target="_top">http://www.lua.org/download.html</a></p><p>Note that ModSecurity requires the dynamic libraries. These are not built by default in the source distribution, so the binary distribution is recommended.</p></li><li><p>libcurl v7.15.1 or higher</p><p>If you will be using the ModSecurity Log Collector (mlogc) to send audit logs to a central repository, then you will also need the curl library.</p><p><a href="http://curl.haxx.se/libcurl/" target="_top">http://curl.haxx.se/libcurl/</a></p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>Many have had issues with libcurl linked with the GnuTLS library for SSL/TLS support. It is recommended that the openssl library be used for SSL/TLS support in libcurl.</p></div></li></ol></div><p>ModSecurity installation consists of the following steps:</p><div class="orderedlist"><ol type="1"><li><p>Stop Apache httpd</p></li><li><p>Unpack the ModSecurity archive</p></li><li><p>Building differs for UNIX (or UNIX-like) operating systems and Windows.</p><div class="itemizedlist"><ul type="disc"><li><p>UNIX</p><div class="orderedlist"><ol type="a"><li><p>Run the configure script to generate a Makefile. Typically no options are needed.</p><p><code class="literal">./configure</code></p><p>Options are available for more customization (use <code class="literal">./configure --help</code> for a full list), but typically you will only need to specify the location of the <code class="literal">apxs</code> command installed by Apache httpd with the <code class="literal">--with-apxs</code> option.</p><p><code class="literal">./configure --with-apxs=/path/to/httpd-2.x.y/bin/apxs</code></p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>There are certain configure options that are meant for debugging an other development use. If enabled, these options can substantially impact performance. These options include all <code class="literal">--debug-*</code> options as well as the <code class="literal">--enable-performance-measurements</code> options.</p></div></li><li><p>Compile with: <code class="literal">make</code></p></li><li><p>Optionally test with: <code class="literal">make test</code></p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>This is step is still a bit experimental. If you have problems, please send the full output and error from the build to the support list. Most common issues are related to not finding the required headers and/or libraries.</p></div></li><li><p>Optionally build the ModSecurity Log Collector with: <code class="literal">make mlogc</code></p></li><li><p>Optionally install <code class="literal">mlogc</code>: Review the <code class="literal">INSTALL</code> file included in the apache2/mlogc-src directory in the distribution.</p></li><li><p>Install the ModSecurity module with: <code class="literal">make install</code></p></li></ol></div></li><li><p>Windows (MS VC++ 8)</p><div class="orderedlist"><ol type="a"><li><p>Edit <code class="literal">Makefile.win</code> to configure the Apache base and library paths.</p></li><li><p>Compile with: <code class="literal">nmake -f Makefile.win</code></p></li><li><p>Install the ModSecurity module with: <code class="literal">nmake -f Makefile.win install</code></p></li><li><p>Copy the <code class="literal">libxml2.dll</code> and <code class="literal">lua5.1.dll</code> to the Apache <code class="literal">bin</code> directory. Alternatively you can follow the step below for using LoadFile to load these libraries.</p></li></ol></div></li></ul></div></li><li><p>Edit the main Apache httpd config file (usually <code class="literal">httpd.conf</code>)</p><p>On UNIX (and Windows if you did not copy the DLLs as stated above) you must load libxml2 and lua5.1 before ModSecurity with something like this:</p><p><pre class="programlisting">LoadFile /usr/lib/libxml2.so LoadFile /usr/lib/liblua5.1.so</pre></p><p>Load the ModSecurity module with:<pre class="programlisting">LoadModule security2_module modules/mod_security2.so</pre></p></li><li><p>Configure ModSecurity</p></li><li><p>Start Apache httpd</p></li><li><p>You should now have ModSecurity 2.x up and running.</p></li></ol></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>If you have compiled Apache yourself you might experience problems compiling ModSecurity against PCRE. This is because Apache bundles PCRE but this library is also typically provided by the operating system. I would expect most (all) vendor-packaged Apache distributions to be configured to use an external PCRE library (so this should not be a problem).</p><p>You want to avoid Apache using the bundled PCRE library and ModSecurity linking against the one provided by the operating system. The easiest way to do this is to compile Apache against the PCRE library provided by the operating system (or you can compile it against the latest PCRE version you downloaded from the main PCRE distribution site). You can do this at configure time using the<code class="literal"> --with-pcre</code> switch. If you are not in a position to recompile Apache, then, to compile ModSecurity successfully, you'd still need to have access to the bundled PCRE headers (they are available only in the Apache source code) and change the include path for ModSecurity (as you did in step 7 above) to point to them (via the <code class="literal">--with-pcre</code> ModSecurity configure option).</p><p>Do note that if your Apache is using an external PCRE library you can compile ModSecurity with <code class="literal">WITH_PCRE_STUDY</code> defined,which would possibly give you a slight performance edge in regular expression processing.</p><p>Non-gcc compilers may have problems running out-of-the-box as the current build system was designed around the gcc compiler and some compiler/linker flags may differ. To use a non-gcc compiler you may need some manual Makefile tweaks if issues cannot be solved by exporting custom CFLAGS and CPPFLAGS environment variables.</p><p>If you are upgrading from ModSecurity 1.x, please refer to the migration matrix at <a href="http://www.modsecurity.org/documentation/ModSecurity-Migration-Matrix.pdf" target="_top">http://www.modsecurity.org/documentation/ModSecurity-Migration-Matrix.pdf</a></p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="configuration-directives"></a>Configuration Directives</h2></div></div><div></div></div><p>The following section outlines all of the ModSecurity directives. Most of the ModSecurity directives can be used inside the various Apache Scope Directives such as <code class="literal">VirtualHost</code>, <code class="literal">Location</code>, <code class="literal">LocationMatch</code>, <code class="literal">Directory</code>, etc... There are others, however, that can only be used once in the main configuration file. This information is specified in the Scope sections below. The first version to use a given directive is given in the Version sections below.</p><p>These rules, along with the Core rules files, should be contained is files outside of the httpd.conf file and called up with Apache "Include" directives. This allows for easier updating/migration of the rules. If you create your own custom rules that you would like to use with the Core rules, you should create a file called - <code class="filename">modsecurity_crs_15_customrules.conf</code> and place it in the same directory as the Core rules files. By using this file name, your custom rules will be called up after the standard ModSecurity Core rules configuration file but before the other Core rules. This allows your rules to be evaluated first which can be useful if you need to implement specific "allow" rules or to correct any false positives in the Core rules as they are applied to your site.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>It is highly encouraged that you do not edit the Core rules files themselves but rather place all changes (such as <code class="literal">SecRuleRemoveByID</code>, etc...) in your custom rules file. This will allow for easier upgrading as newer Core rules are released by Breach Security on the ModSecurity website.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N101B0"></a><code class="literal">SecAction</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Unconditionally processes the action list it receives as the first and only parameter. It accepts one parameter, the syntax of which is identical to the third parameter of<code class="literal"> SecRule</code>.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecAction action1,action2,action3</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecAction nolog,phase:1,initcol:RESOURCE=%{REQUEST_FILENAME}</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> Any</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> None</p><p>SecAction is best used when you unconditionally execute an action. This is explicit triggering whereas the normal Actions are conditional based on data inspection of the request/response. This is a useful directive when you want to run certain actions such as <code class="literal">initcol</code> to initialize collections.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N101E1"></a><code class="literal">SecArgumentSeparator</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Specifies which character to use as separator for<code class="literal"> application/x-www-form-urlencoded</code> content. Defaults to <code class="literal">&</code>. Applications are sometimes (very rarely) written to use a semicolon (<code class="literal">;</code>).</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecArgumentSeparator character</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecArgumentSeparator ;</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> Any</p><p><span class="emphasis"><em>Scope:</em></span> Main</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> None</p><p>This directive is needed if a backend web application is using a non-standard argument separator. If this directive is not set properly for each web application, then ModSecurity will not be able to parse the arguments appropriately and the effectiveness of the rule matching will be significantly decreased.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10216"></a><code class="literal">SecAuditEngine</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configures the audit logging engine.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecAuditEngine On|Off|RelevantOnly</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecAuditEngine On</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> Can be set/changed with the "<code class="literal">ctl</code>" action for the current transaction.</p><p>Example: The following example shows the various audit directives used together.</p><pre class="programlisting"><span class="emphasis"><em>SecAuditEngine RelevantOnly</em></span> SecAuditLog logs/audit/audit.log SecAuditLogParts ABCFHZ SecAuditLogType concurrent SecAuditLogStorageDir logs/audit <span class="emphasis"><em>SecAuditLogRelevantStatus ^(?:5|4\d[^4])</em></span></pre><p>Possible values are:</p><div class="itemizedlist"><ul type="disc"><li><p><code class="literal">On</code> - log all transactions by default.</p></li><li><p><code class="literal">Off</code> - do not log transactions by default.</p></li><li><p><code class="literal">RelevantOnly</code> - by default only log transactions that have triggered a warning or an error, or have a status code that is considered to be relevant (see<code class="literal"> SecAuditLogRelevantStatus</code>).</p></li></ul></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10263"></a><code class="literal">SecAuditLog</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Defines the path to the main audit log file.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecAuditLog /path/to/auditlog</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecAuditLog /usr/local/apache/logs/audit.log</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> This file is open on startup when the server typically still runs as<span class="emphasis"><em> root</em></span>. You should not allow non-root users to have write privileges for this file or for the directory it is stored in..</p><p>This file will be used to store the audit log entries if serial audit logging format is used. If concurrent audit logging format is used this file will be used as an index, and contain a record of all audit log files created. If you are planning to use Concurrent audit logging and sending your audit log data off to a remote Console host or commercial ModSecurity Management Appliance, then you will need to configure and use the ModSecurity Log Collector (mlogc) and use the following format for the audit log:</p><p><pre class="programlisting">SecAuditLog "|/path/to/mlogc /path/to/mlogc.conf"</pre></p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10293"></a><code class="literal">SecAuditLog2</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Defines the path to the secondary audit log index file when concurrent logging is enabled. See <code class="literal">SecAuditLog2</code> for more details.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecAuditLog2 /path/to/auditlog2</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecAuditLog2 /usr/local/apache/logs/audit2.log</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.1.2</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> A main audit log must be defined via <code class="literal">SecAuditLog</code> before this directive may be used. Additionally, this log is only used for replicating the main audit log index file when concurrent audit logging is used. It will <span class="emphasis"><em>not</em></span> be used for non-concurrent audit logging.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N102C5"></a><code class="literal">SecAuditLogDirMode</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configures the mode (permissions) of any directories created for concurrent audit logs using an octal mode (as used in chmod). See <code class="literal">SecAuditLogFileMode</code> for controlling the mode of audit log files.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecAuditLogDirMode octal_mode|"default"</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecAuditLogDirMode 02750</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.5.10</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> This feature is not available on operating systems not supporting octal file modes. The default mode (0600) only grants read/write access to the account writing the file. If access from another account is needed (using mpm-itk is a good example), then this directive may be required. However, use this directive with caution to avoid exposing potentially sensitive data to unauthorized users. Using the value "default" will revert back to the default setting.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>The process umask may still limit the mode if it is being more restrictive than the mode set using this directive.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N102F3"></a><code class="literal">SecAuditLogFileMode</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configures the mode (permissions) of any files created for concurrent audit logs using an octal mode (as used in chmod). See <code class="literal">SecAuditLogDirMode</code> for controlling the mode of created audit log directories.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecAuditLogFileMode octal_mode|"default"</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecAuditLogFileMode 00640</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.5.10</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> This feature is not available on operating systems not supporting octal file modes. The default mode (0600) only grants read/write access to the account writing the file. If access from another account is needed (using mpm-itk is a good example), then this directive may be required. However, use this directive with caution to avoid exposing potentially sensitive data to unauthorized users. Using the value "default" will revert back to the default setting.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>The process umask may still limit the mode if it is being more restrictive than the mode set using this directive.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10321"></a><code class="literal">SecAuditLogParts</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Defines which part of each transaction are going to be recorded in audit log. Each part is assigned a single letter. If a letter appears in the list then the equivalent part of each transactions will be recorded. See below for the list of all parts.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecAuditLogParts PARTS</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecAuditLogParts ABCFHZ</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> At this time ModSecurity does not log response bodies of stock Apache responses (e.g. <code class="literal">404</code>), or the <code class="literal">Server</code> and <code class="literal">Date</code> response headers.</p><p>Default:<code class="literal"> ABCFHZ</code>.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>Please refer to the ModSecurity Data Formats document for a detailed description of every available part.</p></div><p>Available audit log parts:</p><div class="itemizedlist"><ul type="disc"><li><p><code class="literal">A</code> - audit log header (mandatory)</p></li><li><p><code class="literal">B</code> - request headers</p></li><li><p><code class="literal">C</code> - request body (present only if the request body exists and ModSecurity is configured to intercept it)</p></li><li><p><code class="literal">D</code> - RESERVED for intermediary response headers, not implemented yet.</p></li><li><p><code class="literal">E</code> - intermediary response body (present only if ModSecurity is configured to intercept response bodies, and if the audit log engine is configured to record it). Intermediary response body is the same as the actual response body unless ModSecurity intercepts the intermediary response body, in which case the actual response body will contain the error message (either the Apache default error message, or the ErrorDocument page).</p></li><li><p><code class="literal">F</code> - final response headers (excluding the Date and Server headers, which are always added by Apache in the late stage of content delivery).</p></li><li><p><code class="literal">G</code> - RESERVED for the actual response body, not implemented yet.</p></li><li><p><code class="literal">H</code> - audit log trailer</p></li><li><p><code class="literal">I</code> - This part is a replacement for part C. It will log the same data as C in all cases except when <code class="literal">multipart/form-data</code> encoding in used. In this case it will log a fake <code class="literal">application/x-www-form-urlencoded</code> body that contains the information about parameters but not about the files. This is handy if you don't want to have (often large) files stored in your audit logs.</p></li><li><p><code class="literal">J</code> - RESERVED. This part, when implemented, will contain information about the files uploaded using <code class="literal">multipart/form-data</code> encoding.</p></li><li><p><code class="literal">K</code> - This part contains a full list of every rule that matched (one per line) in the order they were matched. The rules are fully qualified and will thus show inherited actions and default operators. Supported as of v2.5.0</p></li><li><p><code class="literal">Z</code> - final boundary, signifies the end of the entry (mandatory)</p></li></ul></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N103B4"></a><code class="literal">SecAuditLogRelevantStatus</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configures which response status code is to be considered relevant for the purpose of audit logging.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecAuditLogRelevantStatus REGEX</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecAuditLogRelevantStatus ^(?:5|4\d[^4])</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> Must have the <code class="literal">SecAuditEngine</code> set to <code class="literal">RelevantOnly</code>. The parameter is a regular expression.</p><p>The main purpose of this directive is to allow you to configure audit logging for only transactions that generate the specified HTTP Response Status Code. This directive is often used to the decrease the total size of the audit log file. Keep in mind that if this parameter is used, then successful attacks that result in a 200 OK status code will not be logged.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N103E5"></a><code class="literal">SecAuditLogStorageDir</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configures the storage directory where concurrent audit log entries are to be stored.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecAuditLogStorageDir /path/to/storage/dir</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecAuditLogStorageDir /usr/local/apache/logs/audit</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> SecAuditLogType must be set to Concurrent. The directory must already be created before starting Apache and it must be writable by the web server user as new files are generated at runtime.</p><p>As with all logging mechanisms, ensure that you specify a file system location that has adequate disk space and is not on the root partition.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1040E"></a><code class="literal">SecAuditLogType</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configures the type of audit logging mechanism to be used.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecAuditLogType Serial|Concurrent</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecAuditLogType Serial</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> Must specify <code class="literal">SecAuditLogStorageDir</code> if you use concurrent logging.</p><p>Possible values are:</p><div class="orderedlist"><ol type="1"><li><p><code class="literal">Serial</code> - all audit log entries will be stored in the main audit logging file. This is more convenient for casual use but it is slower as only one audit log entry can be written to the file at any one file.</p></li><li><p><code class="literal">Concurrent</code> - audit log entries will be stored in separate files, one for each transaction. Concurrent logging is the mode to use if you are going to send the audit log data off to a remote ModSecurity Console host.</p></li></ol></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1044A"></a><code class="literal">SecCacheTransformations</code> (Deprecated/Experimental)</h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Controls caching of transformations. Caching is off by default starting with 2.5.6, when it was deprecated and downgraded back to experimental.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecCacheTransformations On|Off [options]</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecCacheTransformations On "minlen:64,maxlen:0"</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.5.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> N/A</p><p>First parameter:</p><div class="itemizedlist"><ul type="disc"><li><p><code class="literal">On</code> - cache transformations (per transaction, per phase) allowing identical transformations to be performed only once. (default)</p></li><li><p><code class="literal">Off</code> - do not cache any transformations, forcing all transformations to be performed for each rule executed.</p></li></ul></div><p>The following options are allowed (comma separated):</p><div class="itemizedlist"><ul type="disc"><li><p><code class="literal">incremental:on|off</code> - enabling this option will cache every transformation instead of just the final transformation. (default: off)</p></li><li><p><code class="literal">maxitems:N</code> - do not allow more than N transformations to be cached. The cache will then be disabled. A zero value is interpreted as "unlimited". This option may be useful to limit caching for a form with a large number of ARGS. (default: 512)</p></li><li><p><code class="literal">minlen:N</code> - do not cache the transformation if the value's length is less than N bytes. (default: 32)</p></li><li><p><code class="literal">maxlen:N</code> - do not cache the transformation if the value's length is more than N bytes. A zero value is interpreted as "unlimited". (default: 1024)</p></li></ul></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1049C"></a><code class="literal">SecChrootDir</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configures the directory path that will be used to jail the web server process.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecChrootDir /path/to/chroot/dir</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecChrootDir /chroot</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Main</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> This feature is not available on Windows builds. The internal chroot functionality provided by ModSecurity works great for simple setups. One example of a simple setup is Apache serving static files only, or running scripts using modules.builds. Some problems you might encounter with more complex setups:</p><div class="orderedlist"><ol type="1"><li><p>DNS lookups do not work (this is because this feature requires a shared library that is loaded on demand, after chroot takes place).</p></li><li><p>You cannot send email from PHP because it uses sendmail and sendmail is outside the jail.</p></li><li><p>In some cases Apache graceful (reload) no longer works.</p></li></ol></div><p>You should be aware that the internal chroot feature might not be 100% reliable. Due to the large number of default and third-party modules available for the Apache web server, it is not possible to verify the internal chroot works reliably with all of them. A module, working from within Apache, can do things that make it easy to break out of the jail. In particular, if you are using any of the modules that fork in the module initialisation phase (e.g. <code class="literal">mod_fastcgi</code>, <code class="literal">mod_fcgid</code>, <code class="literal">mod_cgid</code>), you are advised to examine each Apache process and observe its current working directory, process root, and the list of open files. Consider what your options are and make your own decision.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N104DD"></a><code class="literal">SecComponentSignature</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description</em></span>: Appends component signature to the ModSecurity signature.</p><p><span class="emphasis"><em>Syntax</em></span>: <code class="literal">SecComponentSignature "COMPONENT_NAME/X.Y.Z (COMMENT)"</code></p><p><span class="emphasis"><em>Example usage</em></span>: <code class="literal">SecComponentSignature "Core Rules/1.2.3"</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope</em></span>: Main</p><p><span class="emphasis"><em>Version</em></span>: 2.5.0</p><p><span class="emphasis"><em>Dependencies/Notes</em></span>: This directive should be used to make the presence of significant ModSecurity components known. The entire signature will be recorded in transaction audit log. It should be used by ModSecurity module and rule set writers to make debugging easier.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10504"></a><code class="literal">SecContentInjection</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Enables content injection using actions <code class="literal">append</code> and <code class="literal">prepend</code>.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecContentInjection (On|Off)</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecContentInjection On</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope</em></span>: Any</p><p><span class="emphasis"><em>Version</em></span>: 2.5.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> N/A</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10533"></a><code class="literal">SecCookieFormat</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Selects the cookie format that will be used in the current configuration context.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecCookieFormat 0|1</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecCookieFormat 0</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> None</p><p>Possible values are:</p><div class="itemizedlist"><ul type="disc"><li><p><code class="literal">0</code> - use version 0 (Netscape) cookies. This is what most applications use. It is the default value.</p></li><li><p><code class="literal">1</code> - use version 1 cookies.</p></li></ul></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10569"></a><code class="literal">SecDataDir</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Path where persistent data (e.g. IP address data, session data, etc) is to be stored.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecDataDir /path/to/dir</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecDataDir /usr/local/apache/logs/data</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Main</p><p><span class="emphasis"><em>Dependencies/Notes: </em></span> This directive is needed when initcol, setsid an setuid are used. Must be writable by the web server user.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1058C"></a><code class="literal">SecDebugLog</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Path to the ModSecurity debug log file.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecDebugLog /path/to/modsec-debug.log</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecDebugLog /usr/local/apache/logs/modsec-debug.log</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> None</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N105B3"></a><code class="literal">SecDebugLogLevel</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configures the verboseness of the debug log data.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecDebugLogLevel 0|1|2|3|4|5|6|7|8|9</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecDebugLogLevel 4</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> Levels <code class="literal">1 - 3</code> are always sent to the Apache error log. Therefore you can always use level <code class="literal">0</code> as the default logging level in production. Level <code class="literal">5</code> is useful when debugging. It is not advisable to use higher logging levels in production as excessive logging can slow down server significantly.</p><p>Possible values are:</p><div class="itemizedlist"><ul type="disc"><li><p><code class="literal">0</code> - no logging.</p></li><li><p><code class="literal">1</code> - errors (intercepted requests) only.</p></li><li><p><code class="literal">2</code> - warnings.</p></li><li><p><code class="literal">3</code> - notices.</p></li><li><p><code class="literal">4</code> - details of how transactions are handled.</p></li><li><p><code class="literal">5</code> - as above, but including information about each piece of information handled.</p></li><li><p><code class="literal">9</code> - log everything, including very detailed debugging information.</p></li></ul></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10613"></a><code class="literal">SecDefaultAction</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Defines the default action to take on a rule match.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecDefaultAction action1,action2,action3</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecDefaultAction log,auditlog,deny,status:403,phase:2</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> Any</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> Rules following a <code class="literal">SecDefaultAction</code> directive will inherit this setting unless a specific action is specified for an individual rule or until another <code class="literal">SecDefaultAction</code> is specified. Take special note that in the logging disruptive actions are not allowed, but this can inadvertently be inherited using a disruptive action in <code class="literal">SecDefaultAction</code>.</p><p>The default value is minimal (differing from previous versions):</p><pre class="programlisting">SecDefaultAction phase:2,log,auditlog,pass</pre><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p><code class="literal">SecDefaultAction</code> must specify a disruptive action and a processing phase and cannot contain metadata actions.</p></div><div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Warning</h3><p><code class="literal">SecDefaultAction</code> is <span class="emphasis"><em>not</em></span> inherited across configuration contexts. (For an example of why this may be a problem for you, read the following ModSecurity Blog entry <a href="http://blog.modsecurity.org/2008/07/modsecurity-tri.html" target="_top">http://blog.modsecurity.org/2008/07/modsecurity-tri.html</a>).</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1065E"></a><code class="literal">SecGeoLookupDb</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Defines the path to the geographical database file.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecGeoLookupDb /path/to/db</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecGeoLookupDb /usr/local/geo/data/GeoLiteCity.dat</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.5.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> Check out <code class="literal">maxmind.com</code> for free database files.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10689"></a><code class="literal">SecGuardianLog</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configuration directive to use the httpd-guardian script to monitor for Denial of Service (DoS) attacks.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecGuardianLog |/path/to/httpd-guardian</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecGuardianLog |/usr/local/apache/bin/httpd-guardian</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Main</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> By default httpd-guardian will defend against clients that send more than 120 requests in a minute, or more than 360 requests in five minutes.</p><p>Since 1.9, ModSecurity supports a new directive, SecGuardianLog, that is designed to send all access data to another program using the piped logging feature. Since Apache is typically deployed in a multi-process fashion, making information sharing difficult, the idea is to deploy a single external process to observe all requests in a stateful manner, providing additional protection.</p><p>Development of a state of the art external protection tool will be a focus of subsequent ModSecurity releases. However, a fully functional tool is already available as part of the <a href="http://www.apachesecurity.net/tools/" target="_top">Apache httpd tools project</a>. The tool is called httpd-guardian and can be used to defend against Denial of Service attacks. It uses the blacklist tool (from the same project) to interact with an iptables-based (Linux) or pf-based (*BSD) firewall, dynamically blacklisting the offending IP addresses. It can also interact with SnortSam (http://www.snortsam.net). Assuming httpd-guardian is already configured (look into the source code for the detailed instructions) you only need to add one line to your Apache configuration to deploy it:</p><pre class="programlisting">SecGuardianLog |/path/to/httpd-guardian</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N106BC"></a><code class="literal">SecMarker</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Adds a fixed rule marker in the ruleset to be used as a target in a <code class="literal">skipAfter</code> action. A <code class="literal">SecMarker</code> directive essentially creates a rule that does nothing and whose only purpose it to carry the given ID.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecMarker ID</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecMarker 9999</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> Any</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.5.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> None</p><p><pre class="programlisting">SecRule REQUEST_URI "^/$" \ "chain,t:none,t:urlDecode,t:lowercase,t:normalisePath,<span class="emphasis"><em>skipAfter:99</em></span>" SecRule REMOTE_ADDR "^127\.0\.0\.1$" "chain" SecRule REQUEST_HEADERS:User-Agent \ "^Apache \(internal dummy connection\)$" "t:none" SecRule &REQUEST_HEADERS:Host "@eq 0" \ "deny,log,status:400,id:08,severity:4,msg:'Missing a Host Header'" SecRule &REQUEST_HEADERS:Accept "@eq 0" \ "log,deny,log,status:400,id:15,msg:'Request Missing an Accept Header'" <span class="emphasis"><em> SecMarker 99</em></span></pre></p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N106F4"></a><code class="literal">SecPcreMatchLimit</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span>Sets the the match limit in the PCRE library. See the pcre_extra field in the pcreapi man page.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecPcreMatchLimit value</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecPcreMatchLimit 1500</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Global</p><p><span class="emphasis"><em>Version:</em></span> 2.5.12</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> Default is set at compile (1500 by default)</p><p>The <code class="literal">--enable-pcre-match-limit=val</code> configure option will set a custom default and the <code class="literal">--disable-pcre-match-limit</code> option will resort to the compiled PCRE library default.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10725"></a><code class="literal">SecPcreMatchLimitRecursion</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span>Sets the the match limit recursion in the PCRE library. See the pcre_extra field in the pcreapi man page.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecPcreMatchLimitRecursion value</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecPcreMatchLimitRecursion 1500</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Global</p><p><span class="emphasis"><em>Version:</em></span> 2.5.12</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> Default is set at compile (1500 by default)</p><p>The <code class="literal">--enable-pcre-match-limit-recursion=val</code> configure option will set a custom default and the <code class="literal">--disable-pcre-match-limit-recursion</code> option will resort to the compiled PCRE library default.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10756"></a><code class="literal">SecPdfProtect</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Enables the PDF XSS protection functionality. Once enabled access to PDF files is tracked. Direct access attempts are redirected to links that contain one-time tokens. Requests with valid tokens are allowed through unmodified. Requests with invalid tokens are also allowed through but with forced download of the PDF files. This implementation uses response headers to detect PDF files and thus can be used with dynamically generated PDF files that do not have the <code class="filename">.pdf</code> extension in the request URI.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecPdfProtect On|Off</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecPdfProtect On</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.5.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> None</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10781"></a><code class="literal">SecPdfProtectMethod</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configure desired protection method to be used when requests for PDF files are detected. Possible values are <code class="literal">TokenRedirection</code> and <code class="literal">ForcedDownload</code>. The token redirection approach will attempt to redirect with tokens where possible. This allows PDF files to continue to be opened inline but only works for GET requests. Forced download always causes PDF files to be delivered as opaque binaries and attachments. The latter will always be used for non-GET requests. Forced download is considered to be more secure but may cause usability problems for users ("This PDF won't open anymore!").</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecPdfProtectMethod method</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecPdfProtectMethod TokenRedirection</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.5.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> None</p><p><span class="emphasis"><em>Default:</em></span> <code class="literal">TokenRedirection</code></p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N107B7"></a><code class="literal">SecPdfProtectSecret</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Defines the secret that will be used to construct one-time tokens. You should use a reasonably long value for the secret (e.g. 16 characters is good). Once selected the secret should not be changed as it will break the tokens that were sent prior to change. But it's not a big deal even if you change it. It will just force download of PDF files with tokens that were issued in the last few seconds.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecPdfProtectSecret secret</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecPdfProtectSecret MyRandomSecretString</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.5.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> None</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N107DE"></a><code class="literal">SecPdfProtectTimeout</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Defines the token timeout. After token expires it can no longer be used to allow access to PDF file. Request will be allowed through but the PDF will be delivered as attachment.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecPdfProtectTimeout timeout</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecPdfProtectTimeout 10</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.5.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> None</p><p><span class="emphasis"><em>Default:</em></span> <code class="literal">10</code></p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1080C"></a><code class="literal">SecPdfProtectTokenName</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Defines the name of the token. The only reason you would want to change the name of the token is if you wanted to hide the fact you are running ModSecurity. It's a good reason but it won't really help as the adversary can look into the algorithm used for PDF protection and figure it out anyway. It does raise the bar slightly so go ahead if you want to.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecPdfProtectTokenName name</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecPdfProtectTokenName PDFTOKEN</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.5.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> None</p><p><span class="emphasis"><em>Default:</em></span> <code class="literal">PDFTOKEN</code></p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1083A"></a><code class="literal">SecRequestBodyAccess</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configures whether request bodies will be buffered and processed by ModSecurity by default.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecRequestBodyAccess On|Off</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecRequestBodyAccess On</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> This directive is required if you plan to inspect <code class="literal">POST_PAYLOAD</code>. This directive must be used along with the "phase:2" processing phase action and <code class="literal">REQUEST_BODY</code> variable/location. If any of these 3 parts are not configured, you will not be able to inspect the request bodies.</p><p>Possible values are:</p><div class="itemizedlist"><ul type="disc"><li><p><code class="literal">On</code> - access request bodies.</p></li><li><p><code class="literal">Off</code> - do not attempt to access request bodies.</p></li></ul></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10878"></a><code class="literal">SecRequestBodyLimit</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configures the maximum request body size ModSecurity will accept for buffering.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecRequestBodyLimit NUMBER_IN_BYTES</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecRequestBodyLimit 134217728</code></p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> 131072 KB (134217728 bytes) is the default setting. Anything over this limit will be rejected with status code 413 Request Entity Too Large. There is a hard limit of 1 GB.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1089B"></a><code class="literal">SecRequestBodyNoFilesLimit</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configures the maximum request body size ModSecurity will accept for buffering, excluding the size of files being transported in the request. This directive comes handy to further reduce susceptibility to DoS attacks when someone is sending request bodies of very large sizes. Web applications that require file uploads must configure <code class="literal">SecRequestBodyLimit</code> to a high value. Since large files are streamed to disk file uploads will not increase memory consumption. However, it's still possible for someone to take advantage of a large request body limit and send non-upload requests with large body sizes. This directive eliminates that loophole.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecRequestBodyNoFilesLimit NUMBER_IN_BYTES</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecRequestBodyLimit 131072</code></p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.5.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> 1 MB (1048576 bytes) is the default setting. This value is very conservative. For most applications you should be able to reduce it down to 128 KB or lower. Anything over the limit will be rejected with status code <code class="literal">413 Request Entity Too Large</code>. There is a hard limit of 1 GB.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N108C6"></a><code class="literal">SecRequestBodyInMemoryLimit</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configures the maximum request body size ModSecurity will store in memory.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecRequestBodyInMemoryLimit NUMBER_IN_BYTES</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecRequestBodyInMemoryLimit 131072</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> None</p><p>By default the limit is 128 KB:</p><pre class="programlisting"># Store up to 128 KB in memory SecRequestBodyInMemoryLimit 131072</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N108F2"></a><code class="literal">SecResponseBodyLimit</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configures the maximum response body size that will be accepted for buffering.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecResponseBodyLimit NUMBER_IN_BYTES</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecResponseBodyLimit 524228</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> Anything over this limit will be rejected with status code 500 Internal Server Error. This setting will not affect the responses with MIME types that are not marked for buffering. There is a hard limit of 1 GB.</p><p>By default this limit is configured to 512 KB:</p><pre class="programlisting"># Buffer response bodies of up to 512 KB in length SecResponseBodyLimit 524288</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1091E"></a><code class="literal">SecResponseBodyLimitAction</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description</em></span>: Controls what happens once a response body limit, configured with <code class="literal">SecResponseBodyLimit</code>, is encountered. By default ModSecurity will reject a response body that is longer than specified. Some web sites, however, will produce very long responses making it difficult to come up with a reasonable limit. Such sites would have to raise the limit significantly to function properly defying the purpose of having the limit in the first place (to control memory consumption). With the ability to choose what happens once a limit is reached site administrators can choose to inspect only the first part of the response, the part that can fit into the desired limit, and let the rest through. Some could argue that allowing parts of responses to go uninspected is a weakness. This is true in theory but only applies to cases where the attacker controls the output (e.g. can make it arbitrary long). In such cases, however, it is not possible to prevent leakage anyway. The attacker could compress, obfuscate, or even encrypt data before it is sent back, and therefore bypass any monitoring device.</p><p><span class="emphasis"><em>Syntax</em></span>: <code class="literal">SecResponseBodyLimitAction Reject|ProcessPartial</code></p><p><span class="emphasis"><em>Example Usage</em></span>: <code class="literal">SecResponseBodyLimitAction ProcessPartial</code></p><p><span class="emphasis"><em>Processing Phase</em></span>: N/A</p><p><span class="emphasis"><em>Scope</em></span>: Any</p><p><span class="emphasis"><em>Version:</em></span> 2.5.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> None</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10949"></a><code class="literal">SecResponseBodyMimeType</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configures which<code class="literal"> MIME</code> types are to be considered for response body buffering.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecResponseBodyMimeType mime/type</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecResponseBodyMimeType text/plain text/html</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> Multiple<code class="literal"> SecResponseBodyMimeType</code> directives can be used to add<code class="literal"> MIME</code> types.</p><p>The default value is <code class="literal">text/plaintext/html</code>:</p><pre class="programlisting">SecResponseBodyMimeType text/plain text/html</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10985"></a><code class="literal">SecResponseBodyMimeTypesClear</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Clears the list of <code class="literal">MIME</code> types considered for response body buffering, allowing you to start populating the list from scratch.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecResponseBodyMimeTypesClear</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecResponseBodyMimeTypesClear</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> None</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N109B0"></a><code class="literal">SecResponseBodyAccess</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configures whether response bodies are to be buffer and analysed or not.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecResponseBodyAccess On|Off</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecResponseBodyAccess On</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> This directive is required if you plan to inspect HTML responses. This directive must be used along with the "phase:4" processing phase action and RESPONSE_BODY variable/location. If any of these 3 parts are not configured, you will not be able to inspect the response bodies.</p><p>Possible values are:</p><div class="itemizedlist"><ul type="disc"><li><p><code class="literal">On</code> - access response bodies (but only if the MIME type matches, see above).</p></li><li><p><code class="literal">Off</code> - do not attempt to access response bodies.</p></li></ul></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N109E6"></a><code class="literal">SecRule</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> <code class="literal">SecRule</code> is the main ModSecurity directive. It is used to analyse data and perform actions based on the results.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecRule VARIABLES OPERATOR [ACTIONS]</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecRule REQUEST_URI "attack" \</code></p><p><code class="literal"> "phase:1,t:none,t:urlDecode,t:lowercase,t:normalisePath"</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> Any</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> None</p><p>In general, the format of this rule is as follows:</p><pre class="programlisting">SecRule VARIABLES OPERATOR [ACTIONS]</pre><p>The second part, <code class="literal">OPERATOR</code>, specifies how they are going to be checked. The third (optional) part, <code class="literal">ACTIONS</code>, specifies what to do whenever the operator used performs a successful match against a variable.</p><div class="section" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="N10A24"></a>Variables in rules</h4></div></div><div></div></div><p>The first part,<code class="literal"> VARIABLES</code>, specifies which variables are to be checked. For example, the following rule will reject a transaction that has the word<span class="emphasis"><em> dirty</em></span> in the URI:</p><pre class="programlisting">SecRule ARGS dirty</pre><p>Each rule can specify one or more variables:</p><pre class="programlisting">SecRule ARGS|REQUEST_HEADERS:User-Agent dirty</pre><p>There is a third format supported by the selection operator - XPath expression. XPath expressions can only used against the special variable XML, which is available only of the request body was processed as XML.</p><pre class="programlisting">SecRule XML:/xPath/Expression dirty</pre><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>Not all collections support all selection operator format types. You should refer to the documentation of each collection to determine what is and isn't supported.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="N10A40"></a>Collections</h4></div></div><div></div></div><p>A variable can contain one or many pieces of data, depending on the nature of the variable and the way it is used. We've seen examples of both approaches in the previous section. When a variable can contain more than one value we refer to it as a <span class="emphasis"><em>collection</em></span>.</p><p>Collections are always expanded before a rule is run. For example, the following rule:</p><pre class="programlisting">SecRule ARGS dirty</pre><p>will be expanded to:</p><pre class="programlisting">SecRule ARGS:p dirty SecRule ARGS:q dirty</pre><p>in a requests that has only two parameters, named <code class="literal">p</code> and <code class="literal">q</code>.</p><p>Collections come in several flavours:</p><div class="variablelist"><dl><dt><span class="term">Read-only</span></dt><dd><p>Created at runtime using transaction data. For example: <code class="literal">ARGS</code> (contains a list of all request parameter values) and <code class="literal">REQUEST_HEADERS</code> (contains a list of all request header values).</p></dd><dt><span class="term">Transient Read/Write</span></dt><dd><p>The <code class="literal">TX</code> collection is created (empty) for every transaction. Rules can read from it and write to it (using the <code class="literal">setvar</code> action, for example), but the information stored in this collection will not survive the end of transaction.</p></dd><dt><span class="term">Persistent Read/Write</span></dt><dd><p>There are several collections that can be written to, but which are persisted to the storage backend. These collections are used to track clients across transactions. Examples of collections that fall into this type are <code class="literal">IP</code>, <code class="literal">SESSION</code> and <code class="literal">USER</code>.</p></dd></dl></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="N10A8D"></a>Operators in rules</h4></div></div><div></div></div><p>In the simplest possible case you will use a regular expression pattern as the second rule parameter. This is what we've done in the examples above. If you do this ModSecurity assumes you want to use the <code class="literal">rx</code> (regular expression) operator. You can also explicitly specify the operator you want to use by using <code class="literal">@</code>, followed by the name of an operator, at the beginning of the second <code class="literal">SecRule</code> parameter:</p><pre class="programlisting">SecRule ARGS "@rx dirty"</pre><p>Note how we had to use double quotes to delimit the second rule parameter. This is because the second parameter now has whitespace in it. Any number of whitespace characters can follow the name of the operator. If there are any non-whitespace characters there, they will all be treated as a special parameter to the operator. In the case of the regular expression operator the special parameter is the pattern that will be used for comparison.</p><p>The @ can be the second character if you are using negation to negate the result returned by the operator:</p><pre class="programlisting">SecRule &ARGS "!@rx ^0$"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="N10AA8"></a>Operator negation</h4></div></div><div></div></div><p>Operator results can be negated by using an exclamation mark at the beginning of the second parameter. The following rule matches if the word <code class="literal">dirty</code> does <span class="emphasis"><em>not</em></span> appear in the <code class="literal">User-Agent</code> request header:</p><pre class="programlisting">SecRule REQUEST_HEADERS:User-Agent !dirty</pre><p>You can use the exclamation mark in combination with any parameter. If you do, the exclamation mark needs to go first, followed by the explicit operator reference. The following rule has the same effect as the previous example:</p><pre class="programlisting">SecRule REQUEST_HEADERS:User-Agent "!@rx dirty"</pre><p>If you need to use negation in a rule that is going to be applied to several variables then it may not be immediately clear what will happen. Consider the following example:</p><pre class="programlisting">SecRule ARGS:p|ARGS:q !dirty</pre><p>The above rule is identical to:</p><pre class="programlisting">SecRule ARGS:p !dirty SecRule ARGS:q !dirty</pre><div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Warning</h3><p>Negation is applied to operations against individual operations, not agains the entire variable list.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="N10ACD"></a>Actions in rules</h4></div></div><div></div></div><p>The third parameter, <code class="literal">ACTIONS</code>, can be omitted only because there is a helper feature that specifies the default action list. If the parameter isn't omitted the actions specified in the parameter will be merged with the default action list to create the actual list of actions that will be processed on a rule match.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10AD6"></a><code class="literal">SecRuleInheritance</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configures whether the current context will inherit rules from the parent context (configuration options are inherited in most cases - you should look up the documentation for every directive to determine if it is inherited or not).</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecRuleInheritance On|Off</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecRuleInheritance Off</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> Any</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> Resource-specific contexts (e.g.<code class="literal"> Location</code>, <code class="literal">Directory</code>, etc) cannot override <span class="emphasis"><em>phase1</em></span> rules configured in the main server or in the virtual server. This is because phase 1 is run early in the request processing process, before Apache maps request to resource. Virtual host context can override phase 1 rules configured in the main server.</p><p>Example: The following example shows where ModSecurity may be enabled in the main Apache configuration scope, however you might want to configure your VirtualHosts differently. In the first example, the first VirtualHost is not inheriting the ModSecurity main config directives and in the second one it is.</p><pre class="programlisting">SecRuleEngine On SecDefaultAction log,pass,phase:2 ... <VirtualHost *:80> ServerName app1.com ServerAlias www.app1.com<span class="emphasis"><em> SecRuleInheritance Off</em></span> SecDefaultAction log,deny,phase:1,redirect:http://www.site2.com ... </VirtualHost> <VirtualHost *:80> ServerName app2.com ServerAlias www.app2.com <span class="emphasis"><em>SecRuleInheritance On</em></span> SecRule ARGS "attack" ... </VirtualHost></pre><p>Possible values are:</p><div class="itemizedlist"><ul type="disc"><li><p><code class="literal">On</code> - inherit rules from the parent context.</p></li><li><p><code class="literal">Off</code> - do not inherit rules from the parent context.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>Configuration contexts are an Apache concept. Directives <code class="literal"><Directory></code>, <code class="literal"><Files></code>, <code class="literal"><Location></code> and <code class="literal"><VirtualHost></code> are all used to create configuration contexts. For more information please go to the Apache documentation section <a href="http://httpd.apache.org/docs/2.0/sections.html" target="_top">Configuration Sections</a>.</p></div></li></ul></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10B39"></a><code class="literal">SecRuleEngine</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configures the rules engine.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecRuleEngine On|Off|DetectionOnly</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecRuleEngine On</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> Any</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> This directive can also be controlled by the ctl action (ctl:ruleEngine=off) for per rule processing.</p><p>Possible values are:</p><div class="itemizedlist"><ul type="disc"><li><p><code class="literal">On</code> - process rules.</p></li><li><p><code class="literal">Off</code> - do not process rules.</p></li><li><p><code class="literal">DetectionOnly</code> - process rules but never intercept transactions, even when rules are configured to do so.</p></li></ul></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10B75"></a><code class="literal">SecRuleRemoveById</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Removes matching rules from the parent contexts.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecRuleUpdateActionById RULEID ACTIONLIST</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecRuleRemoveByID 1 2 "9000-9010"</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> Any</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> This directive supports multiple parameters, where each parameter can either be a rule ID, or a range. Parameters that contain spaces must be delimited using double quotes.</p><pre class="programlisting">SecRuleRemoveById 1 2 5 10-20 "400-556" 673</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10B9F"></a><code class="literal">SecRuleRemoveByMsg</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Removes matching rules from the parent contexts.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecRuleRemoveByMsg REGEX</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecRuleRemoveByMsg "FAIL"</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> Any</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> This directive supports multiple parameters. Each parameter is a regular expression that will be applied to the message (specified using the <code class="literal">msg</code> action).</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10BCA"></a><code class="literal">SecRuleScript</code> (Experimental)</h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> This directive creates a special rule that executes a Lua script to decide whether to match or not. The main difference from <code class="literal">SecRule</code> is that there are no targets nor operators. The script can fetch any variable from the ModSecurity context and use any (Lua) operator to test them. The second optional parameter is the list of actions whose meaning is identical to that of <code class="literal">SecRule</code>.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecRuleScript /path/to/script.lua [ACTIONS]</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecRuleScript "/path/to/file.lua" "block"</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> Any</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.5.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> None</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>All Lua scripts are compiled at configuration time and cached in memory. To reload scripts you must reload the entire ModSecurity configuration by restarting Apache.</p></div><p>Example script:</p><pre class="programlisting">-- Your script must define the <span class="emphasis"><em>main</em></span> entry -- point, as below. function main() -- Log something at level 1. Normally you shouldn't be -- logging anything, especially not at level 1, but this is -- just to show you can. Useful for debugging. m.log(1, "Hello world!"); -- Retrieve one variable. local var1 = m.getvar("REMOTE_ADDR"); -- Retrieve one variable, applying one transformation function. -- The second parameter is a string. local var2 = m.getvar("ARGS", "lowercase"); -- Retrieve one variable, applying several transformation functions. -- The second parameter is now a list. You should note that m.getvar() -- requires the use of comma to separate collection names from -- variable names. This is because only one variable is returned. local var3 = m.getvar("ARGS.p", { "lowercase", "compressWhitespace" } ); -- If you want this rule to match return a string -- containing the error message. The message <span class="emphasis"><em>must</em></span> contain the name -- of the variable where the problem is located. -- return "Variable ARGS:p looks suspicious!" -- Otherwise, simply return nil. return nil; end</pre><p>In this first example we were only retrieving one variable at the time. In this case the name of the variable is known to you. In many cases, however, you will want to examine variables whose names you won't know in advance, for example script parameters.</p><p>Example showing use of <code class="literal">m.getvars()</code> to retrieve many variables at once:</p><pre class="programlisting">function main() -- Retrieve script parameters. local d = m.getvars("ARGS", { "lowercase", "htmlEntityDecode" } ); -- Loop through the paramters. for i = 1, #d do -- Examine parameter value. if (string.find(d[i].value, "<script")) then -- Always specify the name of the variable where the -- problem is located in the error message. return ("Suspected XSS in variable " .. d[i].name .. "."); end end -- Nothing wrong found. return nil; end</pre><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>Go to <a href="http://www.lua.org/" target="_top">http://www.lua.org/</a> to find more about the Lua programming language. The reference manual too is available online, at <a href="http://www.lua.org/manual/5.1/" target="_top">http://www.lua.org/manual/5.1/</a>.</p></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>Lua support is marked as <span class="emphasis"><em>experimental</em></span> as the way the progamming interface may continue to evolve while we are working for the best implementation style. Any user input into the programming interface is appreciated.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10C24"></a><code class="literal">SecRuleUpdateActionById</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Updates the action list of the specified rule.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecRuleRemoveById RULEID ACTIONLIST</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecRuleUpdateActionById 12345 deny,status:403</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> Any</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.5.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> This directive merges the specified action list with the rule's action list. There are two limitations. The rule ID cannot be changed, nor can the phase. Further note that actions that may be specified multiple times are appended to the original.</p><pre class="programlisting">SecAction \ "t:lowercase,phase:2,id:12345,pass,msg:'The Message',log,auditlog" SecRuleUpdateActionById 12345 "t:compressWhitespace,deny,status:403,msg:'A new message'</pre><p>The example above will cause the rule to be executed as if it was specified as follows:</p><pre class="programlisting">SecAction \ "t:lowercase,phase:2,id:12345,log,auditlog,t:compressWhitespace,deny,status:403,msg:'A new message'"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10C53"></a><code class="literal">SecServerSignature</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Instructs ModSecurity to change the data presented in the "Server:" response header token.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecServerSignature "WEB SERVER SOFTWARE"</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecServerSignature "Netscape-Enterprise/6.0"</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Main</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> In order for this directive to work, you must set the Apache ServerTokens directive to Full. ModSecurity will overwrite the server signature data held in this memory space with the data set in this directive. If ServerTokens is not set to Full, then the memory space is most likely not large enough to hold the new data we are looking to insert.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10C7A"></a><code class="literal">SecTmpDir</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configures the directory where temporary files will be created.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecTmpDir /path/to/dir</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecTmpDir /tmp</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> Needs to be writable by the Apache user process. This is the directory location where Apache will swap data to disk if it runs out of memory (more data than what was specified in the SecRequestBodyInMemoryLimit directive) during inspection.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10CA1"></a><code class="literal">SecUploadDir</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configures the directory where intercepted files will be stored.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecUploadDir /path/to/dir</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecUploadDir /tmp</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> This directory must be on the same filesystem as the temporary directory defined with <code class="literal">SecTmpDir</code>. This directive is used with <code class="literal">SecUploadKeepFiles</code>.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10CD0"></a><code class="literal">SecUploadFileLimit</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configures the maximum number of file uploads processed in a multipart POST.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecUploadFileLimit number</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecUploadFileLimit 10</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.5.12</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> The default is set to 100 files, but you are encouraged to reduce this value. Any file over the limit will not be extracted and the <code class="literal">MULTIPART_FILE_LIMIT_EXCEEDED</code> and <code class="literal">MULTIPART_STRICT_ERROR</code> flags will be set. To prevent bypassing any file checks, you must check for one of these flags.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>If the limit is exceeded, the part name and file name will still be recorded in <code class="literal">FILES_NAME</code> and <code class="literal">FILES</code>, the file size will be recorded in <code class="literal">FILES_SIZES</code>, but there will be no record in <code class="literal">FILES_TMPNAMES</code> as a temporary file was not created.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10D12"></a><code class="literal">SecUploadFileMode</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configures the mode (permissions) of any uploaded files using an octal mode (as used in chmod).</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecUploadFileMode octal_mode|"default"</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecUploadFileMode 0640</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.1.6</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> This feature is not available on operating systems not supporting octal file modes. The default mode (0600) only grants read/write access to the account writing the file. If access from another account is needed (using clamd is a good example), then this directive may be required. However, use this directive with caution to avoid exposing potentially sensitive data to unauthorized users. Using the value "default" will revert back to the default setting.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>The process umask may still limit the mode if it is being more restrictive than the mode set using this directive.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10D3C"></a><code class="literal">SecUploadKeepFiles</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configures whether or not the intercepted files will be kept after transaction is processed.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecUploadKeepFiles On|Off|RelevantOnly</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecUploadKeepFiles On</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> This directive requires the storage directory to be defined (using <code class="literal">SecUploadDir</code>).</p><p>Possible values are:</p><div class="itemizedlist"><ul type="disc"><li><p><code class="literal">On</code> - Keep uploaded files.</p></li><li><p><code class="literal">Off</code> - Do not keep uploaded files.</p></li><li><p><code class="literal">RelevantOnly</code> - This will keep only those files that belong to requests that are deemed relevant.</p></li></ul></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10D7C"></a><code class="literal">SecWebAppId</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Creates a partition on the server that belongs to one web application.</p><p><span class="emphasis"><em>Syntax:</em></span> <code class="literal">SecWebAppId "NAME"</code></p><p><span class="emphasis"><em>Example Usage:</em></span> <code class="literal">SecWebAppId "WebApp1"</code></p><p><span class="emphasis"><em>Processing Phase:</em></span> N/A</p><p><span class="emphasis"><em>Scope:</em></span> Any</p><p><span class="emphasis"><em>Version:</em></span> 2.0.0</p><p><span class="emphasis"><em>Dependencies/Notes:</em></span> Partitions are used to avoid collisions between session IDs and user IDs. This directive must be used if there are multiple applications deployed on the same server. If it isn't used, a collision between session IDs might occur. The default value is<code class="literal"> default</code>. Example:</p><pre class="programlisting"><VirtualHost *:80> ServerName app1.com ServerAlias www.app1.com <span class="emphasis"><em>SecWebAppId "App1"</em></span> SecRule REQUEST_COOKIES:PHPSESSID !^$ chain,nolog,pass SecAction setsid:%{REQUEST_COOKIES.PHPSESSID} ... </VirtualHost> <VirtualHost *:80> ServerName app2.com ServerAlias www.app2.com<span class="emphasis"><em> SecWebAppId "App2"</em></span> SecRule REQUEST_COOKIES:PHPSESSID !^$ chain,nolog,pass SecAction setsid:%{REQUEST_COOKIES.PHPSESSID} ... </VirtualHost></pre><p>In the two examples configurations shown, SecWebAppId is being used in conjunction with the Apache VirtualHost directives. What this achieves is to create more unique collection names when being hosted on one server. Normally, when setsid is used, ModSecurity will create a collection with the name "SESSION" and it will hold the value specified. With using SecWebAppId as shown in the examples, however, the name of the collection would become "App1_SESSION" and "App2_SESSION".</p><p>SecWebAppId is relevant in two cases:</p><div class="orderedlist"><ol type="1"><li><p>You are logging transactions/alerts to the ModSecurity Console and you want to use the web application ID to search only the transactions belonging to that application.</p></li><li><p>You are using the data persistence facility (collections SESSION and USER) and you need to avoid collisions between sessions and users belonging to different applications.</p></li></ol></div></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="processing-phases"></a>Processing Phases</h2></div></div><div></div></div><p>ModSecurity 2.x allows rules to be placed in one of the following five phases:</p><div class="orderedlist"><ol type="1"><li><p>Request headers (<code class="literal">REQUEST_HEADERS</code>)</p></li><li><p>Request body (<code class="literal">REQUEST_BODY</code>)</p></li><li><p>Response headers (<code class="literal">RESPONSE_HEADERS</code>)</p></li><li><p>Response body (<code class="literal">RESPONSE_BODY</code>)</p></li><li><p>Logging (<code class="literal">LOGGING</code>)</p></li></ol></div><p>Below is a diagram of the standard Apache Request Cycle. In the diagram, the 5 ModSecurity processing phases are shown.</p><p><div><img src="apache_request_cycle-modsecurity.jpg" width="495"></div></p><p>In order to select the phase a rule executes during, use the phase action either directly in the rule or in using the <code class="literal">SecDefaultAction</code> directive:</p><pre class="programlisting">SecDefaultAction "log,pass,<span class="emphasis"><em>phase:2</em></span>" SecRule REQUEST_HEADERS:Host "!^$" "deny,<span class="emphasis"><em>phase:1</em></span>"</pre><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>Keep in mind that rules are executed according to phases, so even if two rules are adjacent in a configuration file, but are set to execute in different phases, they would not happen one after the other. The order of rules in the configuration file is important only within the rules of each phase. This is especially important when using the <code class="literal">skip</code> and <code class="literal">skipAfter</code> actions.</p></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>The <code class="literal">LOGGING</code> phase is special. It is executed at the end of each transaction no matter what happened in the previous phases. This means it will be processed even if the request was intercepted or the <code class="literal">allow</code> action was used to pass the transaction through.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10E17"></a>Phase Request Headers</h3></div></div><div></div></div><p>Rules in this phase are processed immediately after Apache completes reading the request headers (post-read-request phase). At this point the request body has not been read yet, meaning not all request arguments are available. Rules should be placed in this phase if you need to have them run early (before Apache does something with the request), to do something before the request body has been read, determine whether or not the request body should be buffered, or decide how you want the request body to be processed (e.g. whether to parse it as XML or not).</p><p><span class="emphasis"><em>Note</em></span></p><p>Rules in this phase can not leverage Apache scope directives (Directory, Location, LocationMatch, etc...) as the post-read-request hook does not have this information yet. The exception here is the VirtualHost directive. If you want to use ModSecurity rules inside Apache locations, then they should run in Phase 2. Refer to the Apache Request Cycle/ModSecurity Processing Phases diagram.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10E21"></a>Phase Request Body</h3></div></div><div></div></div><p>This is the general-purpose input analysis phase. Most of the application-oriented rules should go here. In this phase you are guaranteed to have received the request arguments (provided the request body has been read). ModSecurity supports three encoding types for the request body phase:</p><div class="itemizedlist"><ul type="disc"><li><p><code class="literal">application/x-www-form-urlencoded</code> - used to transfer form data</p></li><li><p><code class="literal">multipart/form-data</code> - used for file transfers</p></li><li><p><code class="literal">text/xml</code> - used for passing XML data</p></li></ul></div><p>Other encodings are not used by most web applications.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10E3B"></a>Phase Response Headers</h3></div></div><div></div></div><p>This phase takes place just before response headers are sent back to the client. Run here if you want to observe the response before that happens, and if you want to use the response headers to determine if you want to buffer the response body. Note that some response status codes (such as 404) are handled earlier in the request cycle by Apache and my not be able to be triggered as expected. Additionally, there are some response headers that are added by Apache at a later hook (such as Date, Server and Connection) that we would not be able to trigger on or sanitize. This should work appropriately in a proxy setup or within phase:5 (logging).</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10E40"></a>Phase Response Body</h3></div></div><div></div></div><p>This is the general-purpose output analysis phase. At this point you can run rules against the response body (provided it was buffered, of course). This is the phase where you would want to inspect the outbound HTML for information disclosure, error messages or failed authentication text.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10E45"></a>Phase Logging</h3></div></div><div></div></div><p>This phase is run just before logging takes place. The rules placed into this phase can only affect how the logging is performed. This phase can be used to inspect the error messages logged by Apache. You cannot deny/block connections in this phase as it is too late. This phase also allows for inspection of other response headers that weren't available during phase:3 or phase:4. Note that you must be careful not to inherit a disruptive action into a rule in this phase as this is a configuration error in ModSecurity 2.5.0 and later versions.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="variables"></a>Variables</h2></div></div><div></div></div><p>The following variables are supported in ModSecurity 2.x:</p><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10E50"></a><code class="literal">ARGS</code></h3></div></div><div></div></div><p><code class="literal">ARGS</code> is a collection and can be used on its own (means all arguments including the POST Payload), with a static parameter (matches arguments with that name), or with a regular expression (matches all arguments with name that matches the regular expression). To look at only the query string or body arguments, see the <code class="literal">ARGS_GET</code> and <code class="literal">ARGS_POST</code> collections.</p><p>Some variables are actually collections, which are expanded into more variables at runtime. The following example will examine all request arguments:<pre class="programlisting">SecRule ARGS dirty</pre> Sometimes, however, you will want to look only at parts of a collection. This can be achieved with the help of the <span class="emphasis"><em>selection operator</em></span>(colon). The following example will only look at the arguments named<code class="literal"> p</code> (do note that, in general, requests can contain multiple arguments with the same name): <pre class="programlisting">SecRule ARGS:p dirty</pre> It is also possible to specify exclusions. The following will examine all request arguments for the word<span class="emphasis"><em> dirty</em></span>, except the ones named <code class="literal">z</code> (again, there can be zero or more arguments named<code class="literal"> z</code>): <pre class="programlisting">SecRule ARGS|!ARGS:z dirty</pre> There is a special operator that allows you to count how many variables there are in a collection. The following rule will trigger if there is more than zero arguments in the request (ignore the second parameter for the time being): <pre class="programlisting">SecRule &ARGS !^0$</pre> And sometimes you need to look at an array of parameters, each with a slightly different name. In this case you can specify a regular expression in the selection operator itself. The following rule will look into all arguments whose names begin with <code class="literal">id_</code>: <pre class="programlisting">SecRule ARGS:/^id_/ dirty</pre></p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>Using <code class="literal">ARGS:p</code> will not result in any invocations against the operator if argument p does not exist.</p><p>In ModSecurity 1.X, the <code class="literal">ARGS</code> variable stood for <code class="literal">QUERY_STRING</code> + <code class="literal">POST_PAYLOAD</code>, whereas now it expands to individual variables.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10EA2"></a><code class="literal">ARGS_COMBINED_SIZE</code></h3></div></div><div></div></div><p>This variable allows you to set more targeted evaluations on the total size of the Arguments as compared with normal Apache LimitRequest directives. For example, you could create a rule to ensure that the total size of the argument data is below a certain threshold (to help prevent buffer overflow issues). Example: Block request if the size of the arguments is above 25 characters.</p><pre class="programlisting">SecRule REQUEST_FILENAME "^/cgi-bin/login\.php" \ "chain,log,deny,phase:2,t:none,t:lowercase,t:normalisePath" SecRule <span class="emphasis"><em>ARGS_COMBINED_SIZE</em></span> "@gt 25"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10EAF"></a><code class="literal">ARGS_NAMES</code></h3></div></div><div></div></div><p>Is a collection of the argument names. You can search for specific argument names that you want to block. In a positive policy scenario, you can also whitelist (using an inverted rule with the ! character) only authorized argument names. Example: This example rule will only allow 2 argument names - p and a. If any other argument names are injected, it will be blocked.</p><pre class="programlisting">SecRule REQUEST_FILENAME "/index.php" \ "chain,log,deny,status:403,phase:2,t:none,t:lowercase,t:normalisePath" SecRule<span class="emphasis"><em> ARGS_NAMES</em></span> "!^(p|a)$" "t:none,t:lowercase"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10EBC"></a><code class="literal">ARGS_GET</code></h3></div></div><div></div></div><p><code class="literal">ARGS_GET</code> is similar to <code class="literal">ARGS</code>, but only contains arguments from the query string.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10ECA"></a><code class="literal">ARGS_GET_NAMES</code></h3></div></div><div></div></div><p><code class="literal">ARGS_GET_NAMES</code> is similar to <code class="literal">ARGS_NAMES</code>, but only contains argument names from the query string.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10ED8"></a><code class="literal">ARGS_POST</code></h3></div></div><div></div></div><p><code class="literal">ARGS_POST</code> is similar to <code class="literal">ARGS</code>, but only contains arguments from the POST body.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10EE6"></a><code class="literal">ARGS_POST_NAMES</code></h3></div></div><div></div></div><p><code class="literal">ARGS_POST_NAMES</code> is similar to <code class="literal">ARGS_NAMES</code>, but only contains argument names from the POST body.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10EF4"></a><code class="literal">AUTH_TYPE</code></h3></div></div><div></div></div><p>This variable holds the authentication method used to validate a user. Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>AUTH_TYPE</em></span> "basic" log,deny,status:403,phase:1,t:lowercase</pre><p><span class="emphasis"><em>Note</em></span></p><p>This data will not be available in a proxy-mode deployment as the authentication is not local. In a proxy-mode deployment, you would need to inspect the <code class="literal">REQUEST_HEADERS:Authorization</code> header.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10F0A"></a><code class="literal">ENV</code></h3></div></div><div></div></div><p>Collection, requires a single parameter (after colon). The <code class="literal">ENV</code> variable is set with setenv and does not give access to the CGI environment variables. Example:</p><pre class="programlisting">SecRule REQUEST_FILENAME "printenv" pass,<span class="emphasis"><em>setenv:tag=suspicious</em></span> SecRule <span class="emphasis"><em>ENV:tag</em></span> "suspicious"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10F1E"></a><code class="literal">FILES</code></h3></div></div><div></div></div><p>Collection. Contains a collection of original file names (as they were called on the remote user's file system). Note: only available if files were extracted from the request body. Example:</p><pre class="programlisting">SecRule<span class="emphasis"><em> FILES</em></span> "\.conf$" log,deny,status:403,phase:2</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10F2B"></a><code class="literal">FILES_COMBINED_SIZE</code></h3></div></div><div></div></div><p>Single value. Total size of the uploaded files. Note: only available if files were extracted from the request body. Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>FILES_COMBINED_SIZE</em></span> "@gt 1000" log,deny,status:403,phase:2</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10F38"></a><code class="literal">FILES_NAMES</code></h3></div></div><div></div></div><p>Collection w/o parameter. Contains a list of form fields that were used for file upload. Note: only available if files were extracted from the request body. Example:</p><pre class="programlisting">SecRule<span class="emphasis"><em> FILES_NAMES</em></span> "^upfile$" log,deny,status:403,phase:2</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10F45"></a><code class="literal">FILES_SIZES</code></h3></div></div><div></div></div><p>Collection. Contains a list of file sizes. Useful for implementing a size limitation on individual uploaded files. Note: only available if files were extracted from the request body. Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>FILES_SIZES</em></span> "@gt 100" log,deny,status:403,phase:2</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10F52"></a><code class="literal">FILES_TMPNAMES</code></h3></div></div><div></div></div><p>Collection. Contains a collection of temporary files' names on the disk. Useful when used together with <code class="literal">@inspectFile.</code> Note: only available if files were extracted from the request body. Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>FILES_TMPNAMES</em></span> "@inspectFile /path/to/inspect_script.pl"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10F63"></a><code class="literal">GEO</code></h3></div></div><div></div></div><p><code class="literal">GEO</code> is a collection populated by the results of the last <code class="literal">@geoLookup</code> operator. The collection can be used to match geographical fields looked from an IP address or hostname.</p><p>Available since ModSecurity 2.5.0.</p><p>Fields:</p><div class="itemizedlist"><ul type="disc"><li><p><span class="emphasis"><em>COUNTRY_CODE:</em></span> Two character country code. EX: US, GB, etc.</p></li><li><p><span class="emphasis"><em>COUNTRY_CODE3:</em></span> Up to three character country code.</p></li><li><p><span class="emphasis"><em>COUNTRY_NAME:</em></span> The full country name.</p></li><li><p><span class="emphasis"><em>COUNTRY_CONTINENT:</em></span> The two character continent that the country is located. EX: EU</p></li><li><p><span class="emphasis"><em>REGION:</em></span> The two character region. For US, this is state. For Canada, providence, etc.</p></li><li><p><span class="emphasis"><em>CITY:</em></span> The city name if supported by the database.</p></li><li><p><span class="emphasis"><em>POSTAL_CODE:</em></span> The postal code if supported by the database.</p></li><li><p><span class="emphasis"><em>LATITUDE:</em></span> The latitude if supported by the database.</p></li><li><p><span class="emphasis"><em>LONGITUDE:</em></span> The longitude if supported by the database.</p></li><li><p><span class="emphasis"><em>DMA_CODE:</em></span> The metropolitan area code if supported by the database. (US only)</p></li><li><p><span class="emphasis"><em>AREA_CODE:</em></span> The phone system area code. (US only)</p></li></ul></div><p>Example:</p><pre class="programlisting">SecGeoLookupDb /usr/local/geo/data/GeoLiteCity.dat ... SecRule REMOTE_ADDR "<span class="emphasis"><em>@geoLookup</em></span>" "chain,drop,msg:'Non-GB IP address'" SecRule GEO:COUNTRY_CODE "!@streq GB"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10FB5"></a><code class="literal">HIGHEST_SEVERITY</code></h3></div></div><div></div></div><p>This variable holds the highest severity of any rules that have matched so far. Severities are numeric values and thus can be used with comparison operators such as <code class="literal">@lt</code>, etc.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>Higher severities have a lower numeric value.</p><p>A value of 255 indicates no severity has been set.</p></div><pre class="programlisting">SecRule HIGHEST_SEVERITY "@le 2" "phase:2,deny,status:500,msg:'severity %{HIGHEST_SEVERITY}'"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10FC8"></a><code class="literal">MATCHED_VAR</code></h3></div></div><div></div></div><p>This variable holds the value of the variable that was matched against. It is similar to the TX:0, except it can be used for all operators and does not require that the <code class="literal">capture</code> action be specified.</p><pre class="programlisting">SecRule ARGS pattern chain,deny ... SecRule <span class="emphasis"><em>MATCHED_VAR</em></span> "further scrutiny"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10FD9"></a><code class="literal">MATCHED_VAR_NAME</code></h3></div></div><div></div></div><p>This variable holds the full name of the variable that was matched against.</p><pre class="programlisting">SecRule ARGS pattern setvar:tx.mymatch=%{MATCHED_VAR_NAME} ... SecRule <span class="emphasis"><em>TX:MYMATCH</em></span> "@eq ARGS:param" deny</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10FE6"></a><code class="literal">MODSEC_BUILD</code></h3></div></div><div></div></div><p>This variable holds the ModSecurity build number. This variable is intended to be used to check the build number prior to using a feature that is available only in a certain build. Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>MODSEC_BUILD</em></span> "!@ge 02050102" skipAfter:12345 SecRule ARGS "@pm some key words" id:12345,deny,status:500</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10FF3"></a><code class="literal">MULTIPART_CRLF_LF_LINES</code></h3></div></div><div></div></div><p>This flag variable will be set to <code class="literal">1</code> whenever a multi-part request uses mixed line terminators. The <code class="literal">multipart/form-data</code> RFC requires <code class="literal">CRLF</code> sequence to be used to terminate lines. Since some client implementations use only <code class="literal">LF</code> to terminate lines you might want to allow them to proceed under certain circumstances (if you want to do this you will need to stop using <code class="literal">MULTIPART_STRICT_ERROR</code> and check each multi-part flag variable individually, avoiding <code class="literal">MULTIPART_LF_LINE</code>). However, mixing <code class="literal">CRLF</code> and <code class="literal">LF</code> line terminators is dangerous as it can allow for evasion. Therefore, in such cases, you will have to add a check for <code class="literal">MULTIPART_CRLF_LF_LINES</code>.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1101E"></a><code class="literal">MULTIPART_STRICT_ERROR</code></h3></div></div><div></div></div><p><code class="literal">MULTIPART_STRICT_ERROR</code> will be set to <code class="literal">1</code> when any of the following variables is also set to <code class="literal">1</code>: <code class="literal">REQBODY_PROCESSOR_ERROR</code>, <code class="literal">MULTIPART_BOUNDARY_QUOTED</code>, <code class="literal">MULTIPART_BOUNDARY_WHITESPACE</code>, <code class="literal">MULTIPART_DATA_BEFORE</code>, <code class="literal">MULTIPART_DATA_AFTER</code>, <code class="literal">MULTIPART_HEADER_FOLDING</code>, <code class="literal">MULTIPART_LF_LINE</code>, <code class="literal">MULTIPART_SEMICOLON_MISSING</code> <code class="literal">MULTIPART_INVALID_QUOTING</code> <code class="literal">MULTIPART_INVALID_HEADER_FOLDING</code> <code class="literal">MULTIPART_FILE_LIMIT_EXCEEDED</code>. Each of these variables covers one unusual (although sometimes legal) aspect of the request body in <code class="literal">multipart/form-data format</code>. Your policies should <span class="emphasis"><em>always</em></span> contain a rule to check either this variable (easier) or one or more individual variables (if you know exactly what you want to accomplish). Depending on the rate of false positives and your default policy you should decide whether to block or just warn when the rule is triggered.</p><p>The best way to use this variable is as in the example below:</p><pre class="programlisting">SecRule MULTIPART_STRICT_ERROR "!@eq 0" \ "phase:2,t:none,log,deny,msg:'Multipart request body \ failed strict validation: \ PE %{REQBODY_PROCESSOR_ERROR}, \ BQ %{MULTIPART_BOUNDARY_QUOTED}, \ BW %{MULTIPART_BOUNDARY_WHITESPACE}, \ DB %{MULTIPART_DATA_BEFORE}, \ DA %{MULTIPART_DATA_AFTER}, \ HF %{MULTIPART_HEADER_FOLDING}, \ LF %{MULTIPART_LF_LINE}, \ SM %{MULTIPART_SEMICOLON_MISSING}, \ IQ %{MULTIPART_INVALID_QUOTING}, \ IQ %{MULTIPART_INVALID_HEADER_FOLDING}, \ FE %{MULTIPART_FILE_LIMIT_EXCEEDED}'"</pre><p>The <code class="literal">multipart/form-data</code> parser was upgraded in ModSecurity v2.1.3 to actively look for signs of evasion. Many variables (as listed above) were added to expose various facts discovered during the parsing process. The <code class="literal">MULTIPART_STRICT_ERROR</code> variable is handy to check on all abnormalities at once. The individual variables allow detection to be fine-tuned according to your circumstances in order to reduce the number of false positives. Detailed analysis of various evasion techniques covered will be released as a separated document at a later date.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11072"></a><code class="literal">MULTIPART_UNMATCHED_BOUNDARY</code></h3></div></div><div></div></div><p>Set to <code class="literal">1</code> when, during the parsing phase of a <code class="literal">multipart/request-body</code>, ModSecurity encounters what feels like a boundary but it is not. Such an event may occur when evasion of ModSecurity is attempted.</p><p>The best way to use this variable is as in the example below:</p><pre class="programlisting">SecRule MULTIPART_UNMATCHED_BOUNDARY "!@eq 0" \ "phase:2,t:none,log,deny,msg:'Multipart parser detected a possible unmatched boundary.'"</pre><p>Change the rule from blocking to logging-only if many false positives are encountered.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11088"></a><code class="literal">PATH_INFO</code></h3></div></div><div></div></div><p>Besides passing query information to a script/handler, you can also pass additional data, known as extra path information, as part of the URL. Example:</p><pre class="programlisting">SecRule<span class="emphasis"><em> PATH_INFO</em></span> "^/(bin|etc|sbin|opt|usr)"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11095"></a><code class="literal">QUERY_STRING</code></h3></div></div><div></div></div><p>This variable holds form data passed to the script/handler by appending data after a question mark. Warning: Not URL-decoded. Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>QUERY_STRING</em></span> "attack"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N110A2"></a><code class="literal">REMOTE_ADDR</code></h3></div></div><div></div></div><p>This variable holds the IP address of the remote client. Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>REMOTE_ADDR</em></span> "^192\.168\.1\.101$"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N110AF"></a><code class="literal">REMOTE_HOST</code></h3></div></div><div></div></div><p>If HostnameLookUps are set to On, then this variable will hold the DNS resolved remote host name. If it is set to Off, then it will hold the remote IP address. Possible uses for this variable would be to deny known bad client hosts or network blocks, or conversely, to allow in authorized hosts. Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>REMOTE_HOST</em></span> "\.evil\.network\org$"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N110BC"></a><code class="literal">REMOTE_PORT</code></h3></div></div><div></div></div><p>This variable holds information on the source port that the client used when initiating the connection to our web server. Example: in this example, we are evaluating to see if the <code class="literal">REMOTE_PORT</code> is less than 1024, which would indicate that the user is a privileged user (root).</p><pre class="programlisting">SecRule <span class="emphasis"><em>REMOTE_PORT</em></span> "@lt 1024" phase:1,log,pass,setenv:remote_port=privileged</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N110CD"></a><code class="literal">REMOTE_USER</code></h3></div></div><div></div></div><p>This variable holds the username of the authenticated user. If there are no password (basic|digest) access controls in place, then this variable will be empty. Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>REMOTE_USER</em></span> "admin"</pre><p><span class="emphasis"><em>Note</em></span></p><p>This data will not be available in a proxy-mode deployment as the authentication is not local.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N110DF"></a><code class="literal">REQBODY_PROCESSOR</code></h3></div></div><div></div></div><p>Built-in processors are <code class="literal">URLENCODED</code>,<code class="literal"> MULTIPART</code>, and <code class="literal">XML</code>. Example:</p><pre class="programlisting">SecRule<span class="emphasis"><em> REQBODY_PROCESSOR</em></span> "^XML$ chain SecRule XML "@validateDTD /opt/apache-frontend/conf/xml.dtd"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N110F8"></a><code class="literal">REQBODY_PROCESSOR_ERROR</code></h3></div></div><div></div></div><p>Possible values are 0 (no error) or 1 (error). This variable will be set by request body processors (typically the <code class="classname">multipart/request-data</code> parser or the XML parser) when they fail to properly parse a request payload.</p><p>Example:</p><pre class="programlisting">SecRule<span class="emphasis"><em> REQBODY_PROCESSOR_ERROR</em></span> "@eq 1" deny,phase:2</pre><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>Your policies <span class="emphasis"><em>must</em></span> have a rule to check REQBODY_PROCESSOR_ERROR at the beginning of phase 2. Failure to do so will leave the door open for impedance mismatch attacks. It is possible, for example, that a payload that cannot be parsed by ModSecurity can be successfully parsed by more tolerant parser operating in the application. If your policy dictates blocking then you should reject the request if error is detected. When operating in detection-only mode your rule should alert with high severity when request body processing fails.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11110"></a><code class="literal">REQBODY_PROCESSOR_ERROR_MSG</code></h3></div></div><div></div></div><p>Empty, or contains the error message from the processor. Example:</p><pre class="programlisting">SecRule<span class="emphasis"><em> REQBODY_PROCESSOR_ERROR_MSG</em></span> "failed to parse" t:lowercase</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1111D"></a><code class="literal">REQUEST_BASENAME</code></h3></div></div><div></div></div><p>This variable holds just the filename part of <code class="literal">REQUEST_FILENAME</code> (e.g. index.php).</p><p>Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>REQUEST_BASENAME</em></span> "^login\.php$" phase:2,t:none,t:lowercase</pre><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>Please note that anti-evasion transformations are not applied to this variable by default. <code class="literal">REQUEST_BASENAME</code> will recognise both <code class="literal">/</code> and <code class="literal">\</code> as path separators.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1113F"></a><code class="literal">REQUEST_BODY</code></h3></div></div><div></div></div><p>This variable holds the data in the request body (including <code class="literal">POST_PAYLOAD</code> data). <code class="literal">REQUEST_BODY</code> should be used if the original order of the arguments is important (<code class="literal">ARGS</code> should be used in all other cases). Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>REQUEST_BODY</em></span> "^username=\w{25,}\&password=\w{25,}\&Submit\=login$"</pre><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>This variable is only available if the <code class="literal">URLENCODED</code> request body processor parsed a request body. This will occur by default when an <code class="literal">application/x-www-form-urlencoded</code> is detected, or the <code class="literal">URLENCODED</code> request body parser is forced. As of 2.5.7 it is possible to force the presence of the <code class="literal">REQUEST_BODY</code> variable, but only when there is no request body processor defined, using the <code class="literal">ctl:forceRequestBodyVariable</code> option in the <code class="literal">REQUEST_HEADERS</code> phase.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11173"></a><code class="literal">REQUEST_COOKIES</code></h3></div></div><div></div></div><p>This variable is a collection of all of the cookie data. Example: the following example is using the Ampersand special operator to count how many variables are in the collection. In this rule, it would trigger if the request does not include any Cookie headers.</p><pre class="programlisting">SecRule<span class="emphasis"><em> &REQUEST_COOKIES</em></span> "@eq 0"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11180"></a><code class="literal">REQUEST_COOKIES_NAMES</code></h3></div></div><div></div></div><p>This variable is a collection of the cookie names in the request headers. Example: the following rule will trigger if the JSESSIONID cookie is not present.</p><pre class="programlisting">SecRule<span class="emphasis"><em> &REQUEST_COOKIES_NAMES:JSESSIONID</em></span> "@eq 0"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1118D"></a><code class="literal">REQUEST_FILENAME</code></h3></div></div><div></div></div><p>This variable holds the relative <code class="literal">REQUEST_URI</code> minus the <code class="literal">QUERY_STRING</code> part (e.g. /index.php). Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>REQUEST_FILENAME</em></span> "^/cgi-bin/login\.php$" phase:2,t:none,t:normalisePath</pre><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>Please note that anti-evasion transformations are not used on <code class="literal">REQUEST_FILENAME</code> by default.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N111A9"></a><code class="literal">REQUEST_HEADERS</code></h3></div></div><div></div></div><p>This variable can be used as either a collection of all of the request headers or can be used to specify individual headers (by using REQUEST_HEADERS<span class="emphasis"><em>:Header-Name</em></span>). Example: the first example uses <code class="literal">REQUEST_HEADERS</code> as a collection and is applying the <code class="literal">validateUrlEncoding</code> operator against all headers.</p><pre class="programlisting">SecRule <span class="emphasis"><em>REQUEST_HEADERS</em></span> "@validateUrlEncoding"</pre><p>Example: the second example is targeting only the <code class="literal">Host</code> header.</p><pre class="programlisting">SecRule <span class="emphasis"><em>REQUEST_HEADERS:Host</em></span> "^[\d\.]+$" \ "deny,log,status:400,msg:'Host header is a numeric IP address'"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N111CD"></a><code class="literal">REQUEST_HEADERS_NAMES</code></h3></div></div><div></div></div><p>This variable is a collection of the names of all of the request headers. Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>REQUEST_HEADERS_NAMES</em></span> "^x-forwarded-for" \ "log,deny,status:403,t:lowercase,msg:'Proxy Server Used'"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N111DA"></a><code class="literal">REQUEST_LINE</code></h3></div></div><div></div></div><p>This variable holds the complete request line sent to the server (including the REQUEST_METHOD and HTTP version data). Example: this example rule will trigger if the request method is something other than GET, HEAD, POST or if the HTTP is something other than HTTP/0.9, 1.0 or 1.1.</p><pre class="programlisting">SecRule <span class="emphasis"><em>REQUEST_LINE</em></span> "!(^((?:(?:pos|ge)t|head))|http/(0\.9|1\.0|1\.1)$)" t:none,t:lowercase</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N111E7"></a><code class="literal">REQUEST_METHOD</code></h3></div></div><div></div></div><p>This variable holds the request method used by the client.</p><p>The following example will trigger if the request method is either <code class="literal">CONNECT</code> or TRACE.</p><pre class="programlisting">SecRule <span class="emphasis"><em>REQUEST_METHOD</em></span> "^((?:connect|trace))$" t:none,t:lowercase</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N111FA"></a><code class="literal">REQUEST_PROTOCOL</code></h3></div></div><div></div></div><p>This variable holds the request protocol version information. Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>REQUEST_PROTOCOL</em></span> "!^http/(0\.9|1\.0|1\.1)$" t:none,t:lowercase</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11207"></a><code class="literal">REQUEST_URI</code></h3></div></div><div></div></div><p>This variable holds the full URL including the <code class="literal">QUERY_STRING</code> data (e.g. /index.php?p=X), however it will never contain a domain name, even if it was provided on the request line. It also does not include either the <code class="literal">REQUEST_METHOD</code> or the HTTP version info.</p><p>Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>REQUEST_URI</em></span> "attack" phase:1,t:none,t:urlDecode,t:lowercase,t:normalisePath</pre><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>Please note that anti-evasion transformations are not used on <code class="literal">REQUEST_URI</code> by default.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11225"></a><code class="literal">REQUEST_URI_RAW</code></h3></div></div><div></div></div><p>Same as <code class="literal">REQUEST_URI</code> but will contain the domain name if it was provided on the request line (e.g. http://www.example.com/index.php?p=X).</p><p>Example:</p><pre class="programlisting">SecRule<span class="emphasis"><em> REQUEST_URI_RAW</em></span> "http:/" phase:1,t:none,t:urlDecode,t:lowercase,t:normalisePath</pre><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>Please note that anti-evasion transformations are not used on <code class="literal">REQUEST_URI_RAW</code> by default.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1123F"></a><code class="literal">RESPONSE_BODY</code></h3></div></div><div></div></div><p>This variable holds the data for the response payload.</p><p>Example:</p><pre class="programlisting">SecRule<span class="emphasis"><em> RESPONSE_BODY</em></span> "ODBC Error Code"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1124E"></a><code class="literal">RESPONSE_CONTENT_LENGTH</code></h3></div></div><div></div></div><p>Response body length in bytes. Can be available starting with phase 3 but it does not have to be (as the length of response body is not always known in advance.) If the size is not known this variable will contain a zero. If <code class="literal">RESPONSE_CONTENT_LENGTH</code> contains a zero in phase 5 that means the actual size of the response body was 0.</p><p>The value of this variable can change between phases if the body is modified. For example, in embedded mode <code class="literal">mod_deflate</code> can compress the response body between phases 4 and 5.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1125F"></a><code class="literal">RESPONSE_CONTENT_TYPE</code></h3></div></div><div></div></div><p>Response content type. Only available starting with phase 3.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11266"></a><code class="literal">RESPONSE_HEADERS</code></h3></div></div><div></div></div><p>This variable is similar to the REQUEST_HEADERS variable and can be used in the same manner. Example:</p><pre class="programlisting">SecRule<span class="emphasis"><em> RESPONSE_HEADERS</em></span><span class="emphasis"><em>:X-Cache</em></span> "MISS"</pre><p><span class="emphasis"><em>Note</em></span></p><p>This variable may not have access to some headers when running in embedded-mode. Headers such as Server, Date, Connection and Content-Type are added during a later Apache hook just prior to sending the data to the client. This data should be available, however, either during ModSecurity phase:5 (logging) or when running in proxy-mode.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1127A"></a><code class="literal">RESPONSE_HEADERS_NAMES</code></h3></div></div><div></div></div><p>This variable is a collection of the response header names. Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>RESPONSE_HEADERS_NAMES</em></span> "Set-Cookie"</pre><p><span class="emphasis"><em>Note</em></span></p><p>Same limitations as RESPONSE_HEADERS with regards to access to some headers in embedded-mode.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1128C"></a><code class="literal">RESPONSE_PROTOCOL</code></h3></div></div><div></div></div><p>This variable holds the HTTP response protocol information. Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>RESPONSE_PROTOCOL</em></span> "^HTTP\/0\.9"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11299"></a><code class="literal">RESPONSE_STATUS</code></h3></div></div><div></div></div><p>This variable holds the HTTP response status code as generated by Apache. Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>RESPONSE_STATUS</em></span> "^[45]"</pre><p><span class="emphasis"><em>Note</em></span></p><p>This directive may not work as expected in embedded-mode as Apache handles many of the stock response codes (404, 401, etc...) earlier in Phase 2. This variable should work as expected in a proxy-mode deployment.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N112AB"></a><code class="literal">RULE</code></h3></div></div><div></div></div><p>This variable provides access to the <code class="literal">id</code>, <code class="literal">rev</code>, <code class="literal">severity</code>, <code class="literal">logdata</code>, and <code class="literal">msg</code> fields of the rule that triggered the action. Only available for expansion in action strings (e.g.<code class="literal">setvar:tx.varname=%{rule.id}</code>). Example:</p><pre class="programlisting">SecRule &REQUEST_HEADERS:Host "@eq 0" "log,deny,setvar:tx.varname=<span class="emphasis"><em>%{rule.id}</em></span>"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N112D0"></a><code class="literal">SCRIPT_BASENAME</code></h3></div></div><div></div></div><p>This variable holds just the local filename part of SCRIPT_FILENAME. Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>SCRIPT_BASENAME</em></span> "^login\.php$"</pre><p><span class="emphasis"><em>Note</em></span></p><p>This variable is not available in proxy mode.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N112E2"></a><code class="literal">SCRIPT_FILENAME</code></h3></div></div><div></div></div><p>This variable holds the full path on the server to the requested script. (e.g. SCRIPT_NAME plus the server path). Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>SCRIPT_FILENAME</em></span> "^/usr/local/apache/cgi-bin/login\.php$"</pre><p><span class="emphasis"><em>Note</em></span></p><p>This variable is not available in proxy mode.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N112F4"></a><code class="literal">SCRIPT_GID</code></h3></div></div><div></div></div><p>This variable holds the group id (numerical value) of the group owner of the script. Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>SCRIPT_GID</em></span> "!^46$"</pre><p><span class="emphasis"><em>Note</em></span></p><p>This variable is not available in proxy mode.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11306"></a><code class="literal">SCRIPT_GROUPNAME</code></h3></div></div><div></div></div><p>This variable holds the group name of the group owner of the script. Example:</p><pre class="programlisting">SecRule<span class="emphasis"><em> SCRIPT_GROUPNAME</em></span> "!^apache$"</pre><p><span class="emphasis"><em>Note</em></span></p><p>This variable is not available in proxy mode.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11318"></a><code class="literal">SCRIPT_MODE</code></h3></div></div><div></div></div><p>This variable holds the script's permissions mode data (numerical - 1=execute, 2=write, 4=read and 7=read/write/execute). Example: will trigger if the script has the WRITE permissions set.</p><pre class="programlisting">SecRule <span class="emphasis"><em>SCRIPT_MODE</em></span> "^(2|3|6|7)$"</pre><p><span class="emphasis"><em>Note</em></span></p><p>This variable is not available in proxy mode.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1132A"></a><code class="literal">SCRIPT_UID</code></h3></div></div><div></div></div><p>This variable holds the user id (numerical value) of the owner of the script. Example: the example rule below will trigger if the UID is not 46 (the Apache user).</p><pre class="programlisting">SecRule<span class="emphasis"><em> SCRIPT_UID</em></span> "!^46$"</pre><p><span class="emphasis"><em>Note</em></span></p><p>This variable is not available in proxy mode.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1133C"></a><code class="literal">SCRIPT_USERNAME</code></h3></div></div><div></div></div><p>This variable holds the username of the owner of the script. Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>SCRIPT_USERNAME</em></span> "!^apache$"</pre><p><span class="emphasis"><em>Note</em></span></p><p>This variable is not available in proxy mode.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1134E"></a><code class="literal">SERVER_ADDR</code></h3></div></div><div></div></div><p>This variable contains the IP address of the server. Example:</p><pre class="programlisting">SecRule<span class="emphasis"><em> SERVER_ADDR</em></span> "^192\.168\.1\.100$"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1135B"></a><code class="literal">SERVER_NAME</code></h3></div></div><div></div></div><p>This variable contains the server's hostname or IP address. Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>SERVER_NAME</em></span> "hostname\.com$"</pre><p><span class="emphasis"><em>Note</em></span></p><p>This data is taken from the Host header submitted in the client request.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1136D"></a><code class="literal">SERVER_PORT</code></h3></div></div><div></div></div><p>This variable contains the local port that the web server is listening on. Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>SERVER_PORT</em></span> "^80$"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1137A"></a><code class="literal">SESSION</code></h3></div></div><div></div></div><p>This variable is a collection, available only after <code class="literal">setsid</code> is executed. Example: the following example shows how to initialize a SESSION collection with setsid, how to use setvar to increase the session.score values, how to set the session.blocked variable and finally how to deny the connection based on the session:blocked value.</p><pre class="programlisting">SecRule REQUEST_COOKIES:PHPSESSID !^$ chain,nolog,pass SecAction setsid:%{REQUEST_COOKIES.PHPSESSID} SecRule REQUEST_URI "^/cgi-bin/finger$" \ "phase:2,t:none,t:lowercase,t:normalisePath,pass,log,setvar:<span class="emphasis"><em>session.score</em></span>=+10" SecRule<span class="emphasis"><em> SESSION:SCORE</em></span> "@gt 50" "pass,log,setvar:<span class="emphasis"><em>session.blocked</em></span>=1" SecRule<span class="emphasis"><em> SESSION:BLOCKED</em></span> "@eq 1" "log,deny,status:403"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11394"></a><code class="literal">SESSIONID</code></h3></div></div><div></div></div><p>This variable is the value set with <code class="literal">setsid</code>. Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>SESSIONID</em></span> !^$ chain,nolog,pass SecRule REQUEST_COOKIES:PHPSESSID !^$ SecAction setsid:%{REQUEST_COOKIES.PHPSESSID}</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N113A5"></a><code class="literal">TIME</code></h3></div></div><div></div></div><p>This variable holds a formatted string representing the time (hour:minute:second). Example:</p><pre class="programlisting">SecRule<span class="emphasis"><em> TIME</em></span> "^(([1](8|9))|([2](0|1|2|3))):\d{2}:\d{2}$"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N113B2"></a><code class="literal">TIME_DAY</code></h3></div></div><div></div></div><p>This variable holds the current date (1-31). Example: this rule would trigger anytime between the 10th and 20th days of the month.</p><pre class="programlisting">SecRule <span class="emphasis"><em>TIME_DAY</em></span> "^(([1](0|1|2|3|4|5|6|7|8|9))|20)$"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N113BF"></a><code class="literal">TIME_EPOCH</code></h3></div></div><div></div></div><p>This variable holds the time in seconds since 1970. Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>TIME_EPOCH</em></span> "@gt 1000"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N113CC"></a><code class="literal">TIME_HOUR</code></h3></div></div><div></div></div><p>This variable holds the current hour (0-23). Example: this rule would trigger during "off hours".</p><pre class="programlisting">SecRule<span class="emphasis"><em> TIME_HOUR</em></span> "^(0|1|2|3|4|5|6|[1](8|9)|[2](0|1|2|3))$"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N113D9"></a><code class="literal">TIME_MIN</code></h3></div></div><div></div></div><p>This variable holds the current minute (0-59). Example: this rule would trigger during the last half hour of every hour.</p><pre class="programlisting">SecRule <span class="emphasis"><em>TIME_MIN</em></span> "^(3|4|5)"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N113E6"></a><code class="literal">TIME_MON</code></h3></div></div><div></div></div><p>This variable holds the current month (0-11). Example: this rule would match if the month was either November (10) or December (11).</p><pre class="programlisting">SecRule<span class="emphasis"><em> TIME_MON</em></span> "^1"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N113F3"></a><code class="literal">TIME_SEC</code></h3></div></div><div></div></div><p>This variable holds the current second count (0-59). Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>TIME_SEC</em></span> "@gt 30"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11400"></a><code class="literal">TIME_WDAY</code></h3></div></div><div></div></div><p>This variable holds the current weekday (0-6). Example: this rule would trigger only on week-ends (Saturday and Sunday).</p><pre class="programlisting">SecRule <span class="emphasis"><em>TIME_WDAY</em></span> "^(0|6)$"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1140D"></a><code class="literal">TIME_YEAR</code></h3></div></div><div></div></div><p>This variable holds the current four-digit year data. Example:</p><pre class="programlisting">SecRule <span class="emphasis"><em>TIME_YEAR</em></span> "^2006$"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1141A"></a><code class="literal">TX</code></h3></div></div><div></div></div><p>Transaction Collection. This is used to store pieces of data, create a transaction anomaly score, and so on. Transaction variables are set for 1 request/response cycle. The scoring and evaluation will not last past the current request/response process. Example: In this example, we are using setvar to increase the tx.score value by 5 points. We then have a follow-up run that will evaluate the transactional score this request and then it will decided whether or not to allow/deny the request through.</p><p>The following is a list of reserved names in the TX collection:</p><div class="itemizedlist"><ul type="disc"><li><p><code class="literal">TX:0</code> - The matching value when using the <code class="literal">@rx</code> or <code class="literal">@pm</code> operator with the <code class="literal">capture</code> action.</p></li><li><p><code class="literal">TX:1-TX:9</code> - The captured subexpression value when using the <code class="literal">@rx</code> operator with capturing parens and the <code class="literal">capture</code> action.</p></li><li><p><code class="literal">TX:MSC_.*</code> - ModSecurity processing flags.</p><div class="itemizedlist"><ul type="circle"><li><p><code class="literal">MSC_PCRE_LIMITS_EXCEEDED</code> - Set non-zero if PCRE match limits are exceeded. See <code class="literal">SecPcreMatchLimit</code> and <code class="literal">SecPcreMatchLimitRecursion</code>.</p></li></ul></div></li></ul></div><pre class="programlisting">SecRule WEBSERVER_ERROR_LOG "does not exist" "phase:5,pass,<span class="emphasis"><em>setvar:tx.score=+5</em></span>" SecRule<span class="emphasis"><em> TX:SCORE</em></span> "@gt 20" deny,log</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11462"></a><code class="literal">USERID</code></h3></div></div><div></div></div><p>This variable is the value set with <code class="literal">setuid</code>. Example:</p><pre class="programlisting">SecAction setuid:%{REMOTE_USER},nolog SecRule<span class="emphasis"><em> USERID</em></span> "Admin"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11473"></a><code class="literal">WEBAPPID</code></h3></div></div><div></div></div><p>This variable is the value set with <code class="literal">SecWebAppId</code>. Example:</p><pre class="programlisting">SecWebAppId "WebApp1" SecRule<span class="emphasis"><em> WEBAPPID</em></span> "WebApp1" "chain,log,deny,status:403" SecRule REQUEST_HEADERS:Transfer-Encoding "!^$"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11484"></a><code class="literal">WEBSERVER_ERROR_LOG</code></h3></div></div><div></div></div><p>Contains zero or more error messages produced by the web server. Access to this variable is in phase:5 (logging). Example:</p><pre class="programlisting">SecRule<span class="emphasis"><em> WEBSERVER_ERROR_LOG</em></span> "File does not exist" "phase:5,setvar:tx.score=+5"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11491"></a><code class="literal">XML</code></h3></div></div><div></div></div><p>Can be used standalone (as a target for <code class="literal">validateDTD</code> and <code class="literal">validateSchema</code>) or with an XPath expression parameter (which makes it a valid target for any function that accepts plain text). Example using XPath:</p><pre class="programlisting">SecDefaultAction log,deny,status:403,phase:2 SecRule REQUEST_HEADERS:Content-Type ^text/xml$ \ phase:1,t:lowercase,nolog,pass,ctl:requestBodyProcessor=<span class="emphasis"><em>XML</em></span> SecRule REQBODY_PROCESSOR "<span class="emphasis"><em>!^XML$</em></span>" skipAfter:12345 SecRule <span class="emphasis"><em>XML:/employees/employee/name/text()</em></span> Fred SecRule <span class="emphasis"><em>XML:/xq:employees/employee/name/text()</em></span> Fred \ id:12345,xmlns:xq=http://www.example.com/employees</pre><p>The first XPath expression does not use namespaces. It would match against payload such as this one:</p><pre class="programlisting"><employees> <employee> <name>Fred Jones</name> <address location="home"> <street>900 Aurora Ave.</street> <city>Seattle</city> <state>WA</state> <zip>98115</zip> </address> <address location="work"> <street>2011 152nd Avenue NE</street> <city>Redmond</city> <state>WA</state> <zip>98052</zip> </address> <phone location="work">(425)555-5665</phone> <phone location="home">(206)555-5555</phone> <phone location="mobile">(206)555-4321</phone> </employee> </employees></pre><p>The second XPath expression does use namespaces. It would match the following payload:</p><pre class="programlisting"><xq:employees xmlns:xq="http://www.example.com/employees"> <employee> <name>Fred Jones</name> <address location="home"> <street>900 Aurora Ave.</street> <city>Seattle</city> <state>WA</state> <zip>98115</zip> </address> <address location="work"> <street>2011 152nd Avenue NE</street> <city>Redmond</city> <state>WA</state> <zip>98052</zip> </address> <phone location="work">(425)555-5665</phone> <phone location="home">(206)555-5555</phone> <phone location="mobile">(206)555-4321</phone> </employee> </xq:employees></pre><p>Note the different namespace used in the second example.</p><p>To learn more about XPath we suggest the following resources:</p><div class="orderedlist"><ol type="1"><li><p><a href="http://www.w3.org/TR/xpath" target="_top">XPath Standard</a></p></li><li><p><a href="http://www.zvon.org/xxl/XPathTutorial/General/examples.html" target="_top">XPath Tutorial</a></p></li></ol></div></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="transformation-functions"></a>Transformation functions</h2></div></div><div></div></div><p>When ModSecurity receives request or response information, it makes a copy of this data and places it into memory. It is on this data in memory that transformation functions are applied. The raw request/response data is never altered. Transformation functions are used to transform a variable before testing it in a rule.</p><p><span class="emphasis"><em>Note</em></span></p><p>There are no default transformation functions as there were in previous versions of ModSecurity.</p><p>The following rule will ensure that an attacker does not use mixed case in order to evade the ModSecurity rule:</p><p><pre class="programlisting">SecRule ARGS:p "xp_cmdshell" <span class="emphasis"><em>"t:lowercase"</em></span></pre> multiple transformation actions can be used in the same rule, for example the following rule also ensures that an attacker does not use URL encoding (%xx encoding) for evasion. Note the order of the transformation functions, which ensures that a URL encoded letter is first decoded and than translated to lower case.</p><p><pre class="programlisting">SecRule ARGS:p "xp_cmdshell" <span class="emphasis"><em>"t:urlDecode,t:lowercase"</em></span></pre></p><p>One can use the SecDefaultAction command to ensure the translation occurs for every rule until the next. Note that transformation actions are additive, so if a rule explicitly list actions, the translation actions set by SecDefaultAction are still performed.</p><p><pre class="programlisting">SecDefaultAction <span class="emphasis"><em>t:urlDecode,t:lowercase</em></span></pre></p><p>The following transformation functions are supported:</p><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N114EE"></a><code class="literal">base64Decode</code></h3></div></div><div></div></div><p>This function decodes a base64-encoded string.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N114F5"></a><code class="literal">base64Encode</code></h3></div></div><div></div></div><p>This function encodes input string using base64 encoding.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N114FC"></a><code class="literal">compressWhitespace</code></h3></div></div><div></div></div><p>It converts whitespace characters (32, \f, \t, \n, \r, \v, 160) to spaces (ASCII 32) and then compresses multiple consecutive space characters into one.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11503"></a>cssDecode</h3></div></div><div></div></div><p>Decodes CSS-encoded characters, as specified at <a href="http://www.w3.org/TR/REC-CSS2/syndata.html" target="_top">http://www.w3.org/TR/REC-CSS2/syndata.html</a>. This function uses only up to two bytes in the decoding process, meaning it is useful to uncover ASCII characters (that wouldn't normally be encoded) encoded using CSS encoding, or to counter evasion which is a combination of a backslash and non-hexadecimal characters (e.g. <code class="literal">ja\vascript</code> is equivalent to <code class="literal">javascript</code>).</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11514"></a><code class="literal">escapeSeqDecode</code></h3></div></div><div></div></div><p>This function decode ANSI C escape sequences:<code class="literal"> \a</code>,<code class="literal"> \b</code>, <code class="literal">\f</code>, <code class="literal">\n</code>, <code class="literal">\r</code>, <code class="literal">\t</code>, <code class="literal">\v</code>, <code class="literal">\\</code>, <code class="literal">\?</code>, <code class="literal">\'</code>, <code class="literal">\"</code>, <code class="literal">\xHH</code> (hexadecimal), <code class="literal">\0OOO</code> (octal). Invalid encodings are left in the output.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1154F"></a><code class="literal">hexDecode</code></h3></div></div><div></div></div><p>This function decodes a hex-encoded string.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11556"></a><code class="literal">hexEncode</code></h3></div></div><div></div></div><p>This function encodes input as hex-encoded string.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1155D"></a><code class="literal">htmlEntityDecode</code></h3></div></div><div></div></div><p>This function decodes HTML entities present in input. The following variants are supported:</p><div class="itemizedlist"><ul type="disc"><li><p><code class="literal">&#xHH</code> and <code class="literal">&#xHH;</code> (where H is any hexadecimal number)</p></li><li><p><code class="literal">&#DDD</code> and <code class="literal">&#DDD;</code> (where D is any decimal number)</p></li><li><p><code class="literal">&quot</code> and <code class="literal">&quot;</code></p></li><li><p><code class="literal">&nbsp</code> and <code class="literal">&nbsp;</code></p></li><li><p><code class="literal">&lt</code> and <code class="literal">&lt;</code></p></li><li><p><code class="literal">&gt</code> and <code class="literal">&gt;</code></p></li></ul></div><p>This function will convert any entity into a single byte only, possibly resulting in a loss of information. It is thus useful to uncover bytes that would otherwise not need to be encoded, but it cannot do anything with the characters from the range above 255.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1159F"></a><code class="literal">jsDecode</code></h3></div></div><div></div></div><p>Decodes JavaScript escape sequences. If a <code class="literal">\uHHHH</code> code is in the range of <code class="literal">FF01</code>-<code class="literal">FF5E</code> (the full width ASCII codes), then the higher byte is used to detect and adjust the lower byte. Otherwise, only the lower byte will be used and the higher byte zeroed.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N115B2"></a><code class="literal">length</code></h3></div></div><div></div></div><p>This function converts the input to its numeric length (count of bytes).</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N115B9"></a><code class="literal">lowercase</code></h3></div></div><div></div></div><p>This function converts all characters to lowercase using the current C locale.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N115C0"></a><code class="literal">md5</code></h3></div></div><div></div></div><p>This function calculates an MD5 hash from input. Note that the computed hash is in a raw binary form and may need encoded into text to be usable (for example: <code class="literal">t:md5,t:hexEncode</code>).</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N115CB"></a><code class="literal"><code class="literal">none</code></code></h3></div></div><div></div></div><p>Not an actual transformation function, but an instruction to ModSecurity to remove all transformation functions associated with the current rule.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N115D4"></a><code class="literal">normalisePath</code></h3></div></div><div></div></div><p>This function will remove multiple slashes, self-references and directory back-references (except when they are at the beginning of the input).</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N115DB"></a><code class="literal">normalisePathWin</code></h3></div></div><div></div></div><p>Same as <code class="literal">normalisePath</code>, but will first convert backslash characters to forward slashes.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N115E6"></a><code class="literal">parityEven7bit</code></h3></div></div><div></div></div><p>This function calculates even parity of 7-bit data replacing the 8th bit of each target byte with the calculated parity bit.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N115ED"></a><code class="literal">parityOdd7bit</code></h3></div></div><div></div></div><p>This function calculates odd parity of 7-bit data replacing the 8th bit of each target byte with the calculated parity bit.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N115F4"></a><code class="literal">parityZero7bit</code></h3></div></div><div></div></div><p>This function calculates zero parity of 7-bit data replacing the 8th bit of each target byte with a zero parity bit which allows inspection of even/odd parity 7bit data as ASCII7 data.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N115FB"></a><code class="literal">removeNulls</code></h3></div></div><div></div></div><p>This function removes NULL bytes from input.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11602"></a><code class="literal">removeWhitespace</code></h3></div></div><div></div></div><p>This function removes all whitespace characters from input.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11609"></a><code class="literal">replaceComments</code></h3></div></div><div></div></div><p>This function replaces each occurrence of a C-style comments (<code class="literal">/* ... */</code>) with a single space (multiple consecutive occurrences of a space will not be compressed). Unterminated comments will too be replaced with a space (ASCII 32). However, a standalone termination of a comment (<code class="literal">*/</code>) will not be acted upon.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11618"></a><code class="literal">replaceNulls</code></h3></div></div><div></div></div><p>This function is enabled by default. It replaces NULL bytes in input with spaces (ASCII 32).</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1161F"></a><code class="literal">urlDecode</code></h3></div></div><div></div></div><p>This function decodes an URL-encoded input string. Invalid encodings (i.e. the ones that use non-hexadecimal characters, or the ones that are at the end of string and have one or two characters missing) will not be converted. If you want to detect invalid encodings use the <code class="literal">@validateUrlEncoding</code> operator. The transformation function should not be used against variables that have already been URL-decoded unless it is your intention to perform URL decoding twice!</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1162A"></a><code class="literal">urlDecodeUni</code></h3></div></div><div></div></div><p>In addition to decoding <code class="literal">%xx</code> like <code class="literal">urlDecode, urlDecodeUni</code> also decodes <code class="literal">%uXXXX</code> encoding. If the code is in the range of <code class="literal">FF01</code>-<code class="literal">FF5E</code> (the full width ASCII codes), then the higher byte is used to detect and adjust the lower byte. Otherwise, only the lower byte will be used and the higher byte zeroed.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11645"></a><code class="literal">urlEncode</code></h3></div></div><div></div></div><p>This function encodes input using URL encoding.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1164C"></a><code class="literal">sha1</code></h3></div></div><div></div></div><p>This function calculates a SHA1 hash from input. Note that the computed hash is in a raw binary form and may need encoded to be usable (for example: <code class="literal">t:sha1,t:hexEncode</code>).</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11657"></a><code class="literal">trimLeft</code></h3></div></div><div></div></div><p>This function removes whitespace from the left side of input.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1165E"></a><code class="literal">trimRight</code></h3></div></div><div></div></div><p>This function removes whitespace from the right side of input.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11665"></a><code class="literal">trim</code></h3></div></div><div></div></div><p>This function removes whitespace from both the left and right sides of input.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="actions"></a>Actions</h2></div></div><div></div></div><p>Each action belongs to one of five groups:</p><div class="variablelist"><dl><dt><span class="term">Disruptive actions</span></dt><dd><p>Cause ModSecurity to do something. In many cases something means block transaction, but not in all. For example, the allow action is classified as a disruptive action, but it does the opposite of blocking. There can only be one disruptive action per rule (if there are multiple disruptive actions present, or inherited, only the last one will take effect), or rule chain (in a chain, a disruptive action can only appear in the first rule).</p></dd><dt><span class="term">Non-disruptive actions</span></dt><dd><p>Do something, but that something does not and cannot affect the rule processing flow. Setting a variable, or changing its value is an example of a non-disruptive action. Non-disruptive action can appear in any rule, including each rule belonging to a chain.</p></dd><dt><span class="term">Flow actions</span></dt><dd><p>These actions affect the rule flow (for example <code class="literal">skip</code> or <code class="literal">skipAfter</code>).</p></dd><dt><span class="term">Meta-data actions</span></dt><dd><p>Meta-data actions are used to provide more information about rules. Examples include <code class="literal">id</code>, <code class="literal">rev</code>, <code class="literal">severity</code> and <code class="literal">msg</code>.</p></dd><dt><span class="term">Data actions</span></dt><dd><p>Not really actions, these are mere containers that hold data used by other actions. For example, the <code class="literal">status</code> action holds the status that will be used for blocking (if it takes place).</p></dd></dl></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N116AD"></a><code class="literal">allow</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Stops rule processing on a successful match and allows the transaction to proceed.</p><p><span class="emphasis"><em>Action Group:</em></span> Disruptive</p><p>Example:</p><pre class="programlisting">SecRule REMOTE_ADDR "^192\.168\.1\.100$" nolog,phase:1,<span class="emphasis"><em>allow</em></span></pre><p>Prior to ModSecurity 2.5 the <code class="literal">allow</code> action would only affect the current phase. An <code class="literal">allow</code> in phase 1 would skip processing the remaining rules in phase 1 but the rules from phase 2 would execute. Starting with v2.5.0 <code class="literal">allow</code> was enhanced to allow for fine-grained control of what is done. The following rules now apply:</p><div class="orderedlist"><ol type="1"><li><p>If used one its own, like in the example above, <code class="literal">allow</code> will affect the entire transaction, stopping processing of the current phase but also skipping over all other phases apart from the logging phase. (The logging phase is special; it is designed to always execute.)</p></li><li><p>If used with parameter "phase", <code class="literal">allow</code> will cause the engine to stop processing the current phase. Other phases will continue as normal.</p></li><li><p>If used with parameter "request", <code class="literal">allow</code> will cause the engine to stop processing the current phase. The next phase to be processed will be phase <code class="literal">RESPONSE_HEADERS</code>.</p></li></ol></div><p>Examples:</p><pre class="programlisting"># Do not process request but process response. SecAction phase:1,allow:request # Do not process transaction (request and response). SecAction phase:1,allow </pre><p>If you want to allow a response through, put a rule in phase <code class="literal">RESPONSE_HEADERS</code> and simply use <code class="literal">allow</code> on its own:</p><pre class="programlisting"># Allow response through. SecAction phase:3,allow</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N116FD"></a>append</h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Appends text given as parameter to the end of response body. For this action to work content injection must be enabled by setting <code class="literal">SecContentInjection</code> to <code class="literal">On</code>. Also make sure you check the content type of the response before you make changes to it (e.g. you don't want to inject stuff into images).</p><p><span class="emphasis"><em>Action Group:</em></span> Non-disruptive</p><p><span class="emphasis"><em>Processing Phases:</em></span> 3 and 4.</p><p>Example:</p><pre class="programlisting">SecRule RESPONSE_CONTENT_TYPE "^text/html" "nolog,pass,<span class="emphasis"><em>append:'<hr>Footer'</em></span>"</pre><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>While macro expansion is allowed in the additional content, you are strongly cautioned against inserting user defined data fields.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1171F"></a><code class="literal">auditlog</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Marks the transaction for logging in the audit log.</p><p><span class="emphasis"><em>Action Group:</em></span> Non-disruptive</p><p>Example:</p><pre class="programlisting">SecRule REMOTE_ADDR "^192\.168\.1\.100$" <span class="emphasis"><em>auditlog</em></span>,phase:1,allow</pre><p><span class="emphasis"><em>Note</em></span></p><p>The auditlog action is now explicit if log is already specified.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11739"></a><code class="literal">block</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Performs the default disruptive action.</p><p><span class="emphasis"><em>Action Group:</em></span> Disruptive</p><p>It is intended to be used by ruleset writers to signify that the rule was intended to block and leaves the "how" up to the administrator. This action is currently a placeholder which will just be replaced by the action from the last <code class="literal">SecDefaultAction</code> in the same context. Using the <code class="literal">block</code> action with the <code class="literal">SecRuleUpdateActionById</code> directive allows a rule to be reverted back to the previous <code class="literal">SecDefaultAction</code> disruptive action.</p><p>In future versions of ModSecurity, more control and functionality will be added to define "how" to block.</p><p>Examples:</p><p>In the following example, the second rule will "deny" because of the SecDefaultAction disruptive action. The intent being that the administrator could easily change this to another disruptive action without editing the actual rules.</p><pre class="programlisting">### Administrator defines "how" to block (deny,status:403)... SecDefaultAction phase:2,deny,status:403,log,auditlog ### Included from a rulest... # Intent is to warn for this User Agent SecRule REQUEST_HEADERS:User-Agent "perl" "phase:2,<span class="emphasis"><em>pass</em></span>,msg:'Perl based user agent identified'" # Intent is to block for this User Agent, "how" described in SecDefaultAction SecRule REQUEST_HEADERS:User-Agent "nikto" "phase:2,<span class="emphasis"><em>block</em></span>,msg:'Nikto Scanners Identified'"</pre><p>In the following example, The rule is reverted back to the <code class="literal">pass</code> action defined in the SecDefaultAction directive by using the <code class="literal">SecRuleUpdateActionById</code> directive in conjuction with the <code class="literal">block</code> action. This allows an administrator to override an action in a 3rd party rule without modifying the rule itself.</p><pre class="programlisting">### Administrator defines "how" to block (deny,status:403)... SecDefaultAction phase:2,pass,log,auditlog ### Included from a rulest... SecRule REQUEST_HEADERS:User-Agent "nikto" "id:1,phase:2,<span class="emphasis"><em>deny</em></span>,msg:'Nikto Scanners Identified'" ### Added by the administrator SecRuleUpdateActionById 1 "<span class="emphasis"><em>block</em></span>"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1177E"></a><code class="literal">capture</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> When used together with the regular expression operator, capture action will create copies of regular expression captures and place them into the transaction variable collection. Up to ten captures will be copied on a successful pattern match, each with a name consisting of a digit from 0 to 9.</p><p><span class="emphasis"><em>Action Group:</em></span> Non-disruptive</p><p>Example:</p><pre class="programlisting">SecRule REQUEST_BODY "^username=(\w{25,})" phase:2,<span class="emphasis"><em>capture</em></span>,t:none,chain SecRule TX:1 "(?:(?:a(dmin|nonymous)))"</pre><p><span class="emphasis"><em>Note</em></span></p><p>The 0 data captures the entire REGEX match and 1 captures the data in the first parens, etc...</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11798"></a><code class="literal">chain</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Chains the rule where the action is placed with the rule that immediately follows it. The result is called a<span class="emphasis"><em> rule chain</em></span>. Chained rules allow for more complex rule matches where you want to use a number of different VARIABLES to create a better rule and to help prevent false positives.</p><p><span class="emphasis"><em>Action Group:</em></span> Flow</p><p>Example:</p><pre class="programlisting"># Refuse to accept POST requests that do # not specify request body length. Do note that # this rule should be preceeded by a rule that verifies # only valid request methods (e.g. GET, HEAD and POST) are used. SecRule REQUEST_METHOD ^POST$<span class="emphasis"><em> chain</em></span>,t:none SecRule REQUEST_HEADERS:Content-Length ^$ t:none</pre><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>In programming language concepts, think of chained rules somewhat similar to AND conditional statements. The actions specified in the first portion of the chained rule will only be triggered if all of the variable checks return positive hits. If one aspect of the chained rule is negative, then the entire rule chain is negative. Also note that disruptive actions, execution phases, metadata actions (id, rev, msg), skip and skipAfter actions can only be specified on by the chain starter rule.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N117B3"></a><code class="literal">ctl</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> The ctl action allows configuration options to be updated for the transaction.</p><p><span class="emphasis"><em>Action Group:</em></span> Non-disruptive</p><p>Example:</p><pre class="programlisting"># Parse requests with Content-Type "text/xml" as XML SecRule REQUEST_CONTENT_TYPE ^text/xml nolog,pass,<span class="emphasis"><em>ctl:requestBodyProcessor=XML</em></span></pre><p><span class="emphasis"><em>Note</em></span></p><p>The following configuration options are supported:</p><div class="orderedlist"><ol type="1"><li><p><code class="literal">auditEngine</code></p></li><li><p><code class="literal">auditLogParts</code></p></li><li><p><code class="literal">debugLogLevel</code></p></li><li><p><code class="literal">ruleRemoveById</code> (single rule ID, or a single rule ID range accepted as parameter)</p></li><li><p><code class="literal">requestBodyAccess</code></p></li><li><p><code class="literal">forceRequestBodyVariable</code></p></li><li><p><code class="literal">requestBodyLimit</code></p></li><li><p><code class="literal">requestBodyProcessor</code></p></li><li><p><code class="literal">responseBodyAccess</code></p></li><li><p><code class="literal">responseBodyLimit</code></p></li><li><p><code class="literal">ruleEngine</code></p></li></ol></div><p>With the exception of<code class="literal"> requestBodyProcessor</code> and <code class="literal"> forceRequestBodyVariable</code>, each configuration option corresponds to one configuration directive and the usage is identical.</p><p>The <code class="literal">requestBodyProcessor</code> option allows you to configure the request body processor. By default ModSecurity will use the <code class="literal">URLENCODED</code> and<code class="literal"> MULTIPART</code> processors to process an <code class="literal">application/x-www-form-urlencoded</code> and a <code class="literal">multipart/form-data</code> bodies, respectively. A third processor, <code class="literal">XML</code>, is also supported, but it is never used implicitly. Instead you must tell ModSecurity to use it by placing a few rules in the<code class="literal"> REQUEST_HEADERS</code> processing phase. After the request body was processed as XML you will be able to use the XML-related features to inspect it.</p><p>Request body processors will not interrupt a transaction if an error occurs during parsing. Instead they will set variables<code class="literal"> REQBODY_PROCESSOR_ERROR</code> and<code class="literal"> REQBODY_PROCESSOR_ERROR_MSG</code>. These variables should be inspected in the <code class="literal">REQUEST_BODY</code> phase and an appropriate action taken.</p><p>The <code class="literal">forceRequestBodyVariable</code> option allows you to configure the <code class="literal">REQUEST_BODY</code> variable to be set when there is no request body processor configured. This allows for inspection of request bodies of unknown types.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11847"></a><code class="literal">deny</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Stops rule processing and intercepts transaction.</p><p><span class="emphasis"><em>Action Group:</em></span> Disruptive</p><p>Example:</p><pre class="programlisting">SecRule REQUEST_HEADERS:User-Agent "nikto" "log,<span class="emphasis"><em>deny</em></span>,msg:'Nikto Scanners Identified'"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1185C"></a><code class="literal">deprecatevar</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Decrement counter based on its age.</p><p><span class="emphasis"><em>Action Group:</em></span> Non-Disruptive</p><p>Example: The following example will decrement the counter by 60 every 300 seconds.</p><pre class="programlisting">SecAction deprecatevar:session.score=60/300</pre><p><span class="emphasis"><em>Note</em></span></p><p>Counter values are always positive, meaning the value will never go below zero.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11873"></a><code class="literal">drop</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Immediately initiate a "connection close" action to tear down the TCP connection by sending a FIN packet.</p><p><span class="emphasis"><em>Action Group:</em></span> Disruptive</p><p>Example: The following example initiates an IP collection for tracking Basic Authentication attempts. If the client goes over the threshold of more than 25 attempts in 2 minutes, it will DROP subsequent connections.</p><pre class="programlisting">SecAction phase:1,initcol:ip=%{REMOTE_ADDR},nolog SecRule ARGS:login "!^$" \ nolog,phase:1,setvar:ip.auth_attempt=+1,deprecatevar:ip.auth_attempt=20/120 SecRule IP:AUTH_ATTEMPT "@gt 25" \ "log,<span class="emphasis"><em>drop</em></span>,phase:1,msg:'Possible Brute Force Attack'"</pre><p><span class="emphasis"><em>Note</em></span></p><p>This action is currently not available on Windows based builds. This action is extremely useful when responding to both Brute Force and Denial of Service attacks in that, in both cases, you want to minimize both the network bandwidth and the data returned to the client. This action causes error message to appear in the log "(9)Bad file descriptor: core_output_filter: writing data to the network"</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1188D"></a><code class="literal">exec</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Executes an external script/binary supplied as parameter. As of v2.5.0, if the parameter supplied to <code class="literal">exec</code> is a Lua script (detected by the <code class="filename">.lua</code> extension) the script will be processed <span class="emphasis"><em>internally</em></span>. This means you will get direct access to the internal request context from the script. Please read the <code class="literal">SecRuleScript</code> documentation for more details on how to write Lua scripts.</p><p><span class="emphasis"><em>Action Group:</em></span> Non-disruptive</p><p>Example:</p><pre class="programlisting"># The following is going to execute /usr/local/apache/bin/test.sh # as a shell script on rule match. SecRule REQUEST_URI "^/cgi-bin/script\.pl" \ "phase:2,t:none,t:lowercase,t:normalisePath,log,<span class="emphasis"><em>exec:/usr/local/apache/bin/test.sh</em></span>" # The following is going to process /usr/local/apache/conf/exec.lua # internally as a Lua script on rule match. SecRule ARGS:p attack log,<span class="emphasis"><em>exec:/usr/local/apache/conf/exec.lua</em></span></pre><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>The exec action is executed independently from any disruptive actions. External scripts will always be called with no parameters. Some transaction information will be placed in environment variables. All the usual CGI environment variables will be there. You should be aware that forking a threaded process results in all threads being replicated in the new process. Forking can therefore incur larger overhead in multi-threaded operation. The script you execute must write something (anything) to stdout. If it doesn't ModSecurity will assume execution didn't work.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N118B6"></a><code class="literal">expirevar</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Configures a collection variable to expire after the given time in seconds.</p><p><span class="emphasis"><em>Action Group:</em></span> Non-disruptive</p><p>Example:</p><pre class="programlisting">SecRule REQUEST_COOKIES:JSESSIONID "!^$" nolog,phase:1,pass,chain SecAction setsid:%{REQUEST_COOKIES:JSESSIONID} SecRule REQUEST_URI "^/cgi-bin/script\.pl" \ "phase:2,t:none,t:lowercase,t:normalisePath,log,allow,\ setvar:session.suspicious=1,<span class="emphasis"><em>expirevar:session.suspicious=3600</em></span>,phase:1"</pre><p><span class="emphasis"><em>Note</em></span></p><p>You should use expirevar actions at the same time that you use setvar actions in order to keep the indented expiration time. If they are used on their own (perhaps in a SecAction directive) the expire time could get re-set. When variables are removed from collections, and there are no other changes, collections are not written to disk at the end of request. This is because the variables can always be expired again when the collection is read again on a subsequent request.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N118D0"></a><code class="literal">id</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Assigns a unique ID to the rule or chain.</p><p><span class="emphasis"><em>Action Group:</em></span> Meta-data</p><p>Example:</p><pre class="programlisting">SecRule &REQUEST_HEADERS:Host "@eq 0" \ "log,<span class="emphasis"><em>id:60008</em></span>,severity:2,msg:'Request Missing a Host Header'"</pre><p><span class="emphasis"><em>Note</em></span></p><p>These are the reserved ranges:</p><div class="itemizedlist"><ul type="disc"><li><p>1-99,999; reserved for local (internal) use. Use as you see fit but do not use this range for rules that are distributed to others.</p></li><li><p>100,000-199,999; reserved for internal use of the engine, to assign to rules that do not have explicit IDs.</p></li><li><p>200,000-299,999; reserved for rules published at modsecurity.org.</p></li><li><p>300,000-399,999; reserved for rules published at gotroot.com.</p></li><li><p>400,000-419,999; unused (available for reservation).</p></li><li><p>420,000-429,999; reserved for <a href="http://projects.otaku42.de/wiki/ScallyWhack" target="_top">ScallyWhack</a>.</p></li><li><p>430,000-699,999; unused (available for reservation).</p></li><li><p>700,000-799,999; reserved for Ivan Ristic.</p></li><li><p>900,000-999,999; reserved for the <a href="http://www.modsecurity.org/projects/rules/" target="_top">Core Rules</a> project.</p></li><li><p>1,000,000 and above; unused (available for reservation).</p></li></ul></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11912"></a><code class="literal">initcol</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Initialises a named persistent collection, either by loading data from storage or by creating a new collection in memory.</p><p><span class="emphasis"><em>Action Group:</em></span> Non-disruptive</p><p>Example: The following example initiates IP address tracking.</p><pre class="programlisting">SecAction <span class="emphasis"><em>phase:1,initcol:ip=%{REMOTE_ADDR}</em></span>,nolog</pre><p><span class="emphasis"><em>Note</em></span></p><p>Normally you will want to use <span class="emphasis"><em>phase:1</em></span> along with <span class="emphasis"><em>initcol</em></span> so that the collection is available in all phases.</p><p>Collections are loaded into memory when the initcol action is encountered. The collection in storage will be persisted (and the appropriate counters increased) <span class="emphasis"><em>only</em></span> if it was changed during transaction processing.</p><p>See the "Persistant Storage" section for further details.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11939"></a><code class="literal">log</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Indicates that a successful match of the rule needs to be logged.</p><p><span class="emphasis"><em>Action Group:</em></span> Non-disruptive</p><p>Example:</p><pre class="programlisting">SecAction phase:1,initcol:ip=%{REMOTE_ADDR},<span class="emphasis"><em>log</em></span></pre><p><span class="emphasis"><em>Note</em></span></p><p>This action will log matches to the Apache error log file and the ModSecurity audit log.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11952"></a><code class="literal">logdata</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Allows a data fragment to be logged as part of the alert message.</p><p><span class="emphasis"><em>Action Group:</em></span> Non-disruptive</p><p>Example:</p><pre class="programlisting">SecRule &ARGS:p "@eq 0" "log,<span class="emphasis"><em>logdata:'%{TX.0}'"</em></span></pre><p><span class="emphasis"><em>Note</em></span></p><p>The logdata information appears in the error and/or audit log files and is not sent back to the client in response headers. Macro expansion is preformed so you may use variable names such as %{TX.0}, etc. The information is properly escaped for use with logging binary data.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N1196B"></a><code class="literal">msg</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Assigns a custom message to the rule or chain.</p><p><span class="emphasis"><em>Action Group:</em></span> Meta-data</p><p>Example:</p><pre class="programlisting">SecRule &REQUEST_HEADERS:Host "@eq 0" \ "log,id:60008<span class="emphasis"><em>,</em></span>severity:2,<span class="emphasis"><em>msg:'Request Missing a Host Header'"</em></span></pre><p><span class="emphasis"><em>Note</em></span></p><p>The msg information appears in the error and/or audit log files and is not sent back to the client in response headers.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11987"></a><code class="literal">multiMatch</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> If enabled ModSecurity will perform multiple operator invocations for every target, before and after every anti-evasion transformation is performed.</p><p><span class="emphasis"><em>Action Group:</em></span> Non-disruptive</p><p>Example:</p><pre class="programlisting">SecDefaultAction log,deny,phase:1,t:removeNulls,t:lowercase SecRule ARGS "attack" <span class="emphasis"><em>multiMatch</em></span></pre><p><span class="emphasis"><em>Note</em></span></p><p>Normally, variables are evaluated once, only after all transformation functions have completed. With multiMatch, variables are checked against the operator before and after every transformation function that changes the input.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N119A0"></a><code class="literal">noauditlog</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Indicates that a successful match of the rule should not be used as criteria whether the transaction should be logged to the audit log.</p><p><span class="emphasis"><em>Action Group:</em></span> Non-disruptive</p><p>Example:</p><pre class="programlisting">SecRule REQUEST_HEADERS:User-Agent "Test" allow,<span class="emphasis"><em>noauditlog</em></span></pre><p><span class="emphasis"><em>Note</em></span></p><p>If the SecAuditEngine is set to On, all of the transactions will be logged. If it is set to RelevantOnly, then you can control it with the noauditlog action. Even if the noauditlog action is applied to a specific rule and a rule either before or after triggered an audit event, then the transaction will be logged to the audit log. The correct way to disable audit logging for the entire transaction is to use "<code class="literal">ctl:auditEngine=Off</code>"</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N119BD"></a><code class="literal">nolog</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Prevents rule matches from appearing in both the error and audit logs.</p><p><span class="emphasis"><em>Action Group:</em></span> Non-disruptive</p><p>Example:</p><pre class="programlisting">SecRule REQUEST_HEADERS:User-Agent "Test" allow,<span class="emphasis"><em>nolog</em></span></pre><p><span class="emphasis"><em>Note</em></span></p><p>The nolog action also implies noauditlog.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N119D6"></a><code class="literal">pass</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Continues processing with the next rule in spite of a successful match.</p><p><span class="emphasis"><em>Action Group:</em></span> Disruptive</p><p>Example1:</p><pre class="programlisting">SecRule REQUEST_HEADERS:User-Agent "Test" log,<span class="emphasis"><em>pass</em></span></pre><p>When using <span class="emphasis"><em>pass</em></span> with SecRule with multiple targets, <span class="emphasis"><em>all</em></span> targets will be processed and <span class="emphasis"><em>all</em></span> non-disruptive actions will trigger for <span class="emphasis"><em>every</em></span> match found. In the second example the TX:test target would be incremented by 1 for each matching argument.</p><p>Example2:</p><pre class="programlisting">SecRule ARGS "test" log,<span class="emphasis"><em>pass</em></span>,setvar:TX.test=+1</pre><p><span class="emphasis"><em>Note</em></span></p><p>The transaction will not be interrupted but a log will be generated for each matching target (unless logging has been suppressed).</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11A05"></a><code class="literal">pause</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Pauses transaction processing for the specified number of milliseconds.</p><p><span class="emphasis"><em>Action Group:</em></span> Non-disruptive</p><p>Example:</p><pre class="programlisting">SecRule REQUEST_HEADERS:User-Agent "Test" log,deny,status:403,<span class="emphasis"><em>pause:5000</em></span></pre><p><span class="emphasis"><em>Note</em></span></p><p>This feature can be of limited benefit for slowing down Brute Force Scanners, however use with care. If you are under a Denial of Service type of attack, the pause feature may make matters worse as this feature will cause child processes to sit idle until the pause is completed.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11A1E"></a><code class="literal">phase</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Places the rule (or the rule chain) into one of five available processing phases.</p><p><span class="emphasis"><em>Action Group:</em></span> Meta-data</p><p>Example:</p><pre class="programlisting">SecDefaultAction log,deny,<span class="emphasis"><em>phase:1</em></span>,t:removeNulls,t:lowercase SecRule REQUEST_HEADERS:User-Agent "Test" log,deny,status:403</pre><p><span class="emphasis"><em>Note</em></span></p><p>Keep in mind that is you specify the incorrect phase, the target variable that you specify may be empty. This could lead to a false negative situation where your variable and operator (RegEx) may be correct, but it misses malicious data because you specified the wrong phase.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11A38"></a>prepend</h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Prepends text given as parameter to the response body. For this action to work content injection must be enabled by setting <code class="literal">SecContentInjection</code> to <code class="literal">On</code>. Also make sure you check the content type of the response before you make changes to it (e.g. you don't want to inject stuff into images).</p><p><span class="emphasis"><em>Action Group:</em></span> Non-disruptive</p><p><span class="emphasis"><em>Processing Phases:</em></span> 3 and 4.</p><p>Example:</p><pre class="programlisting">SecRule RESPONSE_CONTENT_TYPE ^text/html "phase:3,nolog,pass,<span class="emphasis"><em>prepend:'Header<br>'</em></span>"</pre><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>While macro expansion is allowed in the additional content, you are strongly cautioned against inserting user defined data fields.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11A5A"></a><code class="literal">proxy</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Intercepts transaction by forwarding request to another web server using the proxy backend.</p><p><span class="emphasis"><em>Action Group:</em></span> Disruptive</p><p>Example:</p><pre class="programlisting">SecRule REQUEST_HEADERS:User-Agent "Test" log,<span class="emphasis"><em>proxy:http://www.honeypothost.com/</em></span></pre><p><span class="emphasis"><em>Note</em></span></p><p>For this action to work, mod_proxy must also be installed. This action is useful if you would like to proxy matching requests onto a honeypot webserver.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11A73"></a><code class="literal">redirect</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Intercepts transaction by issuing a redirect to the given location.</p><p><span class="emphasis"><em>Action Group:</em></span> Disruptive</p><p>Example:</p><pre class="programlisting">SecRule REQUEST_HEADERS:User-Agent "Test" \ log,<span class="emphasis"><em>redirect:http://www.hostname.com/failed.html</em></span></pre><p><span class="emphasis"><em>Note</em></span></p><p>If the <code class="literal">status</code> action is present and its value is acceptable (301, 302, 303, or 307) it will be used for the redirection. Otherwise status code 302 will be used.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11A90"></a><code class="literal">rev</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Specifies rule revision.</p><p><span class="emphasis"><em>Action Group:</em></span> Meta-data</p><p>Example:</p><pre class="programlisting">SecRule REQUEST_METHOD "^PUT$" "id:340002,<span class="emphasis"><em>rev:1</em></span>,severity:2,msg:'Restricted HTTP function'"</pre><p><span class="emphasis"><em>Note</em></span></p><p>This action is used in combination with the <code class="literal">id</code> action to allow the same rule ID to be used after changes take place but to still provide some indication the rule changed.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11AAE"></a><code class="literal">sanitiseArg</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Sanitises (replaces each byte with an asterisk) a named request argument prior to audit logging.</p><p><span class="emphasis"><em>Action Group:</em></span> Non-disruptive</p><p>Example:</p><pre class="programlisting">SecAction nolog,phase:2,<span class="emphasis"><em>sanitiseArg:password</em></span></pre><p><span class="emphasis"><em>Note</em></span></p><p>The sanitize actions do not sanitize any data within the actual raw requests but only on the copy of data within memory that is set to log to the audit log. It will not sanitize the data in the modsec_debug.log file (if the log level is set high enough to capture this data).</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11AC7"></a><code class="literal">sanitiseMatched</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Sanitises the variable (request argument, request header, or response header) that caused a rule match.</p><p><span class="emphasis"><em>Action Group:</em></span> Non-disruptive</p><p>Example: This action can be used to sanitise arbitrary transaction elements when they match a condition. For example, the example below will sanitise any argument that contains the word<span class="emphasis"><em> password</em></span> in the name.</p><pre class="programlisting">SecRule ARGS_NAMES password nolog,pass,<span class="emphasis"><em>sanitiseMatched</em></span></pre><p><span class="emphasis"><em>Note</em></span></p><p>Same note as sanitiseArg.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11AE3"></a><code class="literal">sanitiseRequestHeader</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Sanitises a named request header.</p><p><span class="emphasis"><em>Action Group:</em></span> Non-disruptive</p><p>Example: This will sanitise the data in the Authorization header.</p><pre class="programlisting">SecAction log,phase:1,<span class="emphasis"><em>sanitiseRequestHeader:Authorization</em></span></pre><p><span class="emphasis"><em>Note</em></span></p><p>Same note as sanitiseArg.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11AFC"></a><code class="literal">sanitiseResponseHeader</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Sanitises a named response header.</p><p><span class="emphasis"><em>Action Group:</em></span> Non-disruptive</p><p>Example: This will sanitise the Set-Cookie data sent to the client.</p><pre class="programlisting">SecAction log,phase:3,<span class="emphasis"><em>sanitiseResponseHeader:Set-Cookie</em></span></pre><p><span class="emphasis"><em>Note</em></span></p><p>Same note as sanitiseArg.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11B15"></a><code class="literal">severity</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Assigns severity to the rule it is placed with.</p><p><span class="emphasis"><em>Action Group:</em></span> Meta-data</p><p>Example:</p><pre class="programlisting">SecRule REQUEST_METHOD "^PUT$" "id:340002,rev:1,<span class="emphasis"><em>severity:CRITICAL</em></span>,msg:'Restricted HTTP function'"</pre><p><span class="emphasis"><em>Note</em></span></p><p>Severity values in ModSecurity follow those of syslog, as below:</p><div class="itemizedlist"><ul type="disc"><li><p>0 - EMERGENCY</p></li><li><p>1 - ALERT</p></li><li><p>2 - CRITICAL</p></li><li><p>3 - ERROR</p></li><li><p>4 - WARNING</p></li><li><p>5 - NOTICE</p></li><li><p>6 - INFO</p></li><li><p>7 - DEBUG</p></li></ul></div><p>It is possible to specify severity levels using either the numerical values or the text values. You should always specify severity levels using the text values. The use of the numerical values is deprecated (as of v2.5.0) and may be removed in one of the susequent major updates.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11B4A"></a><code class="literal">setuid</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Special-purpose action that initialises the <code class="literal">USER</code> collection.</p><p><span class="emphasis"><em>Action Group:</em></span> Non-disruptive</p><p>Example:</p><pre class="programlisting">SecAction <span class="emphasis"><em>setuid:%{REMOTE_USER}</em></span>,nolog</pre><p><span class="emphasis"><em>Note</em></span></p><p>After initialisation takes place the variable <code class="literal">USERID</code> will be available for use in the subsequent rules.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11B6C"></a><code class="literal">setsid</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Special-purpose action that initialises the <code class="literal">SESSION</code> collection.</p><p><span class="emphasis"><em>Action Group: </em></span>Non-disruptive</p><p>Example:</p><pre class="programlisting"># Initialise session variables using the session cookie value SecRule REQUEST_COOKIES:PHPSESSID !^$ chain,nolog,pass SecAction <span class="emphasis"><em>setsid:%{REQUEST_COOKIES.PHPSESSID}</em></span></pre><p><span class="emphasis"><em>Note</em></span></p><p>On first invocation of this action the collection will be empty (not taking the predefined variables into account - see <code class="literal">initcol</code> for more information). On subsequent invocations the contents of the collection (session, in this case) will be retrieved from storage. After initialisation takes place the variable<code class="literal"> SESSIONID</code> will be available for use in the subsequent rules.This action understands each application maintains its own set of sessions. It will utilise the current web application ID to create a session namespace.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11B91"></a><code class="literal">setenv</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Creates, removes, or updates an environment variable.</p><p><span class="emphasis"><em>Action Group:</em></span> Non-disruptive</p><p>Examples:</p><p>To create a new variable (if you omit the value <code class="literal">1</code> will be used):</p><pre class="programlisting">setenv:name=value</pre><p>To remove a variable:</p><pre class="programlisting">setenv:!name</pre><p><span class="emphasis"><em>Note</em></span></p><p>This action can be used to establish communication with other Apache modules.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11BB3"></a><code class="literal">setvar</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Creates, removes, or updates a variable in the specified collection.</p><p><span class="emphasis"><em>Action Group:</em></span> Non-disruptive</p><p>Examples:</p><p>To create a new variable:</p><pre class="programlisting">setvar:tx.score=10</pre><p>To remove a variable prefix the name with exclamation mark:</p><pre class="programlisting">setvar:!tx.score</pre><p>To increase or decrease variable value use <code class="literal">+</code> and <code class="literal">-</code> characters in front of a numerical value:</p><pre class="programlisting">setvar:tx.score=+5</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11BD9"></a><code class="literal">skip</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Skips one or more rules (or chains) on successful match.</p><p><span class="emphasis"><em>Action Group:</em></span> Flow</p><p>Example:</p><p><pre class="programlisting">SecRule REQUEST_URI "^/$" \ "phase:2,chain,t:none<span class="emphasis"><em>,skip:2</em></span>" SecRule REMOTE_ADDR "^127\.0\.0\.1$" "chain" SecRule REQUEST_HEADERS:User-Agent "^Apache \(internal dummy connection\)$" "t:none" SecRule &REQUEST_HEADERS:Host "@eq 0" \ "deny,log,status:400,id:960008,severity:4,msg:'Request Missing a Host Header'" SecRule &REQUEST_HEADERS:Accept "@eq 0" \ "log,deny,log,status:400,id:960015,msg:'Request Missing an Accept Header'"</pre></p><p><span class="emphasis"><em>Note</em></span></p><p>Skip only applies to the current processing phase and not necessarily the order in which the rules appear in the configuration file. If you group rules by processing phases, then skip should work as expected. This action can not be used to skip rules within one chain. Accepts a single parameter denoting the number of rules (or chains) to skip.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11BF4"></a><code class="literal">skipAfter</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Skips rules (or chains) on successful match resuming rule execution after the specified rule ID or marker (see <code class="literal">SecMarker</code>) is found.</p><p><span class="emphasis"><em>Action Group:</em></span> Flow</p><p>Example:</p><p><pre class="programlisting">SecRule REQUEST_URI "^/$" "chain,t:none,<span class="emphasis"><em>skipAfter:960015</em></span>" SecRule REMOTE_ADDR "^127\.0\.0\.1$" "chain" SecRule REQUEST_HEADERS:User-Agent "^Apache \(internal dummy connection\)$" "t:none" SecRule &REQUEST_HEADERS:Host "@eq 0" \ "deny,log,status:400,id:960008,severity:4,msg:'Request Missing a Host Header'" SecRule &REQUEST_HEADERS:Accept "@eq 0" \ "log,deny,log,status:400,id:960015,msg:'Request Missing an Accept Header'"</pre></p><p><span class="emphasis"><em>Note</em></span></p><p><code class="literal">SkipAfter</code> only applies to the current processing phase and not necessarily the order in which the rules appear in the configuration file. If you group rules by processing phases, then skip should work as expected. This action can not be used to skip rules within one chain. Accepts a single parameter denoting the last rule ID to skip.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11C16"></a><code class="literal">status</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Specifies the response status code to use with actions<code class="literal"> deny</code> and<code class="literal"> redirect</code>.</p><p><span class="emphasis"><em>Action Group:</em></span> Data</p><p>Example:</p><pre class="programlisting">SecDefaultAction log,deny,<span class="emphasis"><em>status:403</em></span>,phase:1</pre><p><span class="emphasis"><em>Note</em></span></p><p>Status actions defined in Apache scope locations (such as Directory, Location, etc...) may be superseded by phase:1 action settings. The Apache ErrorDocument directive will be triggered if present in the configuration. Therefore if you have previously defined a custom error page for a given status then it will be executed and its output presented to the user.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11C38"></a><code class="literal">t</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> This action can be used which transformation function should be used against the specified variables before they (or the results, rather) are run against the operator specified in the rule.</p><p><span class="emphasis"><em>Action Group:</em></span> Non-disruptive</p><p>Example:</p><pre class="programlisting">SecDefaultAction log,deny,phase:1,t:removeNulls,t:lowercase SecRule REQUEST_COOKIES:SESSIONID "47414e81cbbef3cf8366e84eeacba091" \ log,deny,status:403,<span class="emphasis"><em>t:md5,t:hexEncode</em></span></pre><p><span class="emphasis"><em>Note</em></span></p><p>Any transformation functions that you specify in a SecRule will be in addition to previous ones specified in SecDefaultAction. Use of "t:none" will remove all transformation functions for the specified rule.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11C51"></a><code class="literal">tag</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Assigns custom text to a rule or chain.</p><p><span class="emphasis"><em>Action Group:</em></span> Meta-data</p><p>Example:</p><pre class="programlisting">SecRule REQUEST_FILENAME "\b(?:n(?:map|et|c)|w(?:guest|sh)|cmd(?:32)?|telnet|rcmd|ftp)\.exe\b" \ "t:none,t:lowercase,deny,msg:'System Command Access',id:'950002',<span class="emphasis"><em>\ tag:'WEB_ATTACK/FILE_INJECTION',tag:'OWASP/A2'</em></span>,severity:'2'"</pre><p><span class="emphasis"><em>Note</em></span></p><p>The tag information appears in the error and/or audit log files. Its intent is to be used to automate classification of rules and the alerts generated by rules. Multiple tags can be used per rule/chain.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11C6B"></a><code class="literal">xmlns</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> This action should be used together with an XPath expression to register a namespace.</p><p><span class="emphasis"><em>Action Group:</em></span> Data</p><p>Example:</p><pre class="programlisting">SecRule REQUEST_HEADERS:Content-Type "text/xml" \ "phase:1,pass,ctl:requestBodyProcessor=XML,ctl:requestBodyAccess=On,<span class="emphasis"><em> \ xmlns:xsd="http://www.w3.org/2001/XMLSchema"</em></span> SecRule XML:/soap:Envelope/soap:Body/q1:getInput/id() "123" phase:2,deny</pre></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="operators"></a>Operators</h2></div></div><div></div></div><p>A number of operators can be used in rules, as documented below. The operator syntax uses the <code class="literal">@</code> symbol followed by the specific operator name.</p><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11C8A"></a><code class="literal">beginsWith</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> This operator is a string comparison and returns true if the parameter value is found at the beginning of the input. Macro expansion is performed so you may use variable names such as <code class="literal">%{TX.1}</code>, etc.</p><p>Example:</p><pre class="programlisting">SecRule REQUEST_LINE "!<span class="emphasis"><em>@beginsWith GET</em></span>" t:none,deny,status:403 SecRule REQUEST_ADDR "^(.*)\.\d+$" deny,status:403,capture,chain SecRule ARGS:gw "!<span class="emphasis"><em>@beginsWith %{TX.1}</em></span>"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11CA2"></a><code class="literal">contains</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> This operator is a string comparison and returns true if the parameter value is found anywhere in the input. Macro expansion is performed so you may use variable names such as %{TX.1}, etc.</p><p>Example:</p><pre class="programlisting">SecRule REQUEST_LINE "!<span class="emphasis"><em>@contains .php</em></span>" t:none,deny,status:403 SecRule REQUEST_ADDR "^(.*)$" deny,status:403,capture,chain SecRule ARGS:ip "!<span class="emphasis"><em>@contains %{TX.1}</em></span>"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11CB6"></a><code class="literal">endsWith</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> This operator is a string comparison and returns true if the parameter value is found at the end of the input. Macro expansion is performed so you may use variable names such as %{TX.1}, etc.</p><p>Example:</p><pre class="programlisting">SecRule REQUEST_LINE "!<span class="emphasis"><em>@endsWith HTTP/1.1</em></span>" t:none,deny,status:403 SecRule ARGS:route "!<span class="emphasis"><em>@endsWith %{REQUEST_ADDR}</em></span>" t:none,deny,status:403</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11CCA"></a><code class="literal">eq</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> This operator is a numerical comparison and stands for "equal to."</p><p>Example:</p><pre class="programlisting">SecRule &REQUEST_HEADERS_NAMES "<span class="emphasis"><em>@eq</em></span> 15"</pre><p>Macro expansion is performed so you may use variable names such as <code class="literal">%{TX.1}</code>, etc.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11CE1"></a><code class="literal">ge</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> This operator is a numerical comparison and stands for "greater than or equal to."</p><p>Example:</p><pre class="programlisting">SecRule &REQUEST_HEADERS_NAMES "<span class="emphasis"><em>@ge</em></span> 15"</pre><p>Macro expansion is performed so you may use variable names such as <code class="literal">%{TX.1}</code>, etc.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11CF8"></a><code class="literal">geoLookup</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> This operator looks up various data fields from an IP address or hostname in the target data. The results will be captured in the <code class="literal">GEO</code> collection.</p><p>You must provide a database via <code class="literal">SecGeoLookupDb</code> before this operator can be used.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>This operator matches and the action is executed on a <span class="emphasis"><em> successful</em></span> lookup. For this reason, you probably want to use the <span class="emphasis"><em>pass,nolog</em></span> actions. This allows for <code class="literal">setvar</code> and other non-disruptive actions to be executed on a match. If you wish to block on a failed lookup, then do something like this (look for an empty GEO collection):</p><pre class="programlisting">SecGeoLookupDb /usr/local/geo/data/GeoLiteCity.dat ... SecRule REMOTE_ADDR "@geoLookup" "pass,nolog" SecRule &GEO "@eq 0" "deny,status:403,msg:'Failed to lookup IP'"</pre></div><p>See the <code class="literal">GEO</code> variable for an example and more information on various fields available.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11D21"></a><code class="literal">gt</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> This operator is a numerical comparison and stands for "greater than."</p><p>Example:</p><pre class="programlisting">SecRule &REQUEST_HEADERS_NAMES "<span class="emphasis"><em>@gt</em></span> 15"</pre><p>Macro expansion is performed so you may use variable names such as <code class="literal">%{TX.1}</code>, etc.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11D38"></a><code class="literal">inspectFile</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Executes the external script/binary given as parameter to the operator against every file extracted from the request. As of v2.5.0, if the supplied filename is not absolute it is treated as relative to the directory in which the configuration file resides. Also as of v2.5.0, if the filename is determined to be a Lua script (based on its extension) the script will be processed by the internal engine. As such it will have full access to the ModSecurity context.</p><p>Example of using an external binary/script:</p><pre class="programlisting"># Execute external script to validate uploaded files. SecRule FILES_TMPNAMES "<span class="emphasis"><em>@inspectFile</em></span> /opt/apache/bin/inspect_script.pl"</pre><p>Example of using Lua script:</p><pre class="programlisting">SecRule FILES_TMPNANMES "@inspectFile <span class="emphasis"><em>inspect.lua</em></span>"</pre><p>Script <code class="filename">inspect.lua</code>:</p><pre class="programlisting">function main(filename) -- Do something to the file to verify it. In this example, we -- read up to 10 characters from the beginning of the file. local f = io.open(filename, "rb"); local d = f:read(10); f:close(); -- Return null if there is no reason to believe there is ansything -- wrong with the file (no match). Returning any text will be taken -- to mean a match should be trigerred. return null; end</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11D5A"></a><code class="literal">le</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> This operator is a numerical comparison and stands for "less than or equal to."</p><p>Example:</p><pre class="programlisting">SecRule &REQUEST_HEADERS_NAMES "<span class="emphasis"><em>@le</em></span> 15"</pre><p>Macro expansion is performed so you may use variable names such as <code class="literal">%{TX.1}</code>, etc.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11D71"></a><code class="literal">lt</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> This operator is a numerical comparison and stands for "less than."</p><p>Example:</p><pre class="programlisting">SecRule &REQUEST_HEADERS_NAMES "<span class="emphasis"><em>@lt</em></span> 15"</pre><p>Macro expansion is performed so you may use variable names such as <code class="literal">%{TX.1}</code>, etc.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11D88"></a><code class="literal">pm</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Phrase Match operator. This operator uses a set based matching engine (Aho-Corasick) for faster matches of keyword lists. It will match any one of its arguments anywhere in the target value. The match is case insensitive.</p><p>Example:</p><pre class="programlisting">SecRule REQUEST_HEADERS:User-Agent "<span class="emphasis"><em>@pm</em></span> WebZIP WebCopier Webster WebStripper SiteSnagger ProWebWalker CheeseBot" "deny,status:403</pre><p>The above would deny access with 403 if any of the words matched within the User-Agent HTTP header value.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11D9B"></a><code class="literal">pmFromFile</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Phrase Match operator. This operator uses a set based matching engine (Aho-Corasick) for faster matches of keyword lists. This operator is the same as <code class="literal">@pm</code> except that it takes a list of files as arguments. It will match any one of the phrases listed in the file(s) anywhere in the target value.</p><p>Notes:</p><div class="orderedlist"><ol type="1"><li><p>The contents of the files should be one phrase per line. End of line markers will be stripped from the phrases (LF and CRLF), and whitespace is trimmed from both sides of the phrases. Empty lines and comment lines (beginning with a '#') are ignored.</p></li><li><p>To allow easier inclusion of phrase files with rulesets, relative paths may be used to the phrase files. In this case, the path of the file containing the rule is prepended to the phrase file path.</p></li><li><p>To allow easier matching of whole IP addresses, you can add boundary characters to the phrases. For example, use "/1.2.3.4/" instead of "1.2.3.4". You can then insert these characters into the target prior to a match:</p><pre class="programlisting">SecAction "phase:1,pass,nolog,setvar:tx.remote_addr=/%{REMOTE_ADDR}/" SecRule TX:REMOTE_ADDR "<span class="emphasis"><em>@pmFromFile ip-blacklist.txt</em></span>" "deny,status:403 # ip-blacklist.txt contents: # NOTE: All IPs must be prefixed/suffixed with "/" as the rules # will add in this character as a boundary to ensure # the entire IP is matched. # SecAction "phase:1,pass,nolog,setvar:tx.remote_addr='/%{REMOTE_ADDR}/'" /1.2.3.4/ /5.6.7.8/</pre></li></ol></div><p>Example:</p><pre class="programlisting">SecRule REQUEST_HEADERS:User-Agent "<span class="emphasis"><em>@pm</em></span> /path/to/blacklist1 blacklist2" "deny,status:403</pre><p>The above would deny access with 403 if any of the patterns in the two files matched within the User-Agent HTTP header value. The <code class="literal">blacklist2</code> file would need to be placed in the same path as the file containing the rule.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11DCA"></a><code class="literal">rbl</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Look up the parameter in the RBL given as parameter. Parameter can be an IPv4 address, or a hostname.</p><p>Example:</p><pre class="programlisting">SecRule REMOTE_ADDR "<span class="emphasis"><em>@rbl</em></span> sc.surbl.org"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11DDB"></a><code class="literal">rx</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Regular expression operator. This is the default operator, so if the "@" operator is not defined, it is assumed to be rx.</p><p>Example:</p><pre class="programlisting">SecRule REQUEST_HEADERS:User-Agent "<span class="emphasis"><em>@rx</em></span> nikto"</pre><p><span class="emphasis"><em>Note</em></span></p><p>Regular expressions are handled by the PCRE library (<a href="http://www.pcre.org" target="_top">http://www.pcre.org</a>). ModSecurity compiles its regular expressions with the following settings:</p><div class="orderedlist"><ol type="1"><li><p>The entire input is treated as a single line, even when there are newline characters present.</p></li><li><p>All matches are case-sensitive. If you do not care about case sensitivity you either need to implement the <code class="literal">lowercase</code> transformation function, or use the per-pattern<code class="literal">(?i)</code>modifier, as allowed by PCRE.</p></li><li><p>The <code class="literal">PCRE_DOTALL</code> and <code class="literal">PCRE_DOLLAR_ENDONLY</code> flags are set during compilation, meaning a single dot will match any character, including the newlines and a <code class="literal">$</code> end anchor will not match a trailing newline character.</p></li></ol></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11E15"></a><code class="literal">streq</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> This operator is a string comparison and returns true if the parameter value matches the input exactly. Macro expansion is performed so you may use variable names such as %{TX.1}, etc.</p><p>Example:</p><pre class="programlisting">SecRule ARGS:foo "!<span class="emphasis"><em>@streq bar</em></span>" t:none,deny,status:403 SecRule REQUEST_ADDR "^(.*)$" deny,status:403,capture,chain SecRule REQUEST_HEADERS:Ip-Address "!<span class="emphasis"><em>@streq %{TX.1}</em></span>"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11E29"></a><code class="literal">validateByteRange</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Validates the byte range used in the variable falls into the specified range.</p><p>Example:</p><pre class="programlisting">SecRule ARGS:text "<span class="emphasis"><em>@validateByteRange</em></span> 10, 13, 32-126"</pre><p><span class="emphasis"><em>Note</em></span></p><p>You can force requests to consist only of bytes from a certain byte range. This can be useful to avoid stack overflow attacks (since they usually contain "random" binary content). Default range values are 0 and 255, i.e. all byte values are allowed. This directive does not check byte range in a POST payload when <code class="literal">multipart/form-data</code> encoding (file upload) is used. Doing so would prevent binary files from being uploaded. However, after the parameters are extracted from such request they are checked for a valid range.</p><p>validateByteRange is similar to the ModSecurity 1.X SecFilterForceByteRange Directive however since it works in a rule context, it has the following differences:</p><div class="itemizedlist"><ul type="disc"><li><p>You can specify a different range for different variables.</p></li><li><p>It has an "event" context (id, msg....)</p></li><li><p>It is executed in the flow of rules rather than being a built in pre-check.</p></li></ul></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11E4F"></a><code class="literal">validateDTD</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Validates the DOM tree generated by the XML request body processor against the supplied DTD.</p><p>Example:</p><pre class="programlisting">SecDefaultAction log,deny,status:403,phase:2 SecRule REQUEST_HEADERS:Content-Type ^text/xml$ \ phase:1,t:lowercase,nolog,pass,ctl:requestBodyProcessor=XML SecRule REQBODY_PROCESSOR "!^XML$" nolog,pass,skipAfter:12345 SecRule XML "<span class="emphasis"><em>@validateDTD /path/to/apache2/conf/xml.dtd</em></span>" "deny,id:12345"</pre><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>This operator requires request body to be processed as XML.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11E63"></a><code class="literal">validateSchema</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Validates the DOM tree generated by the XML request body processor against the supplied XML Schema.</p><p>Example:</p><pre class="programlisting">SecDefaultAction log,deny,status:403,phase:2 SecRule REQUEST_HEADERS:Content-Type ^text/xml$ \ phase:1,t:lowercase,nolog,pass,ctl:requestBodyProcessor=XML SecRule REQBODY_PROCESSOR "!^XML$" nolog,pass,skipAfter:12345 SecRule XML "<span class="emphasis"><em>@validateSchema /path/to/apache2/conf/xml.xsd</em></span>" "deny,id:12345"</pre><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>This operator requires request body to be processed as XML.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11E77"></a><code class="literal">validateUrlEncoding</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Verifies the encodings used in the variable (if any) are valid.</p><p>Example:</p><pre class="programlisting">SecRule ARGS "<span class="emphasis"><em>@validateUrlEncoding</em></span>"</pre><p><span class="emphasis"><em>Note</em></span></p><p>URL encoding is an HTTP standard for encoding byte values within a URL. The byte is escaped with a % followed by two hexadecimal values (0-F). This directive does not check encoding in a POST payload when the <code class="literal">multipart/form-data</code> encoding (file upload) is used. It is not necessary to do so because URL encoding is not used for this encoding.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11E91"></a><code class="literal">validateUtf8Encoding</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> Verifies the variable is a valid UTF-8 encoded string.</p><p>Example:</p><pre class="programlisting">SecRule ARGS "<span class="emphasis"><em>@validateUtf8Encoding</em></span>"</pre><p><span class="emphasis"><em>Note</em></span></p><p>UTF-8 encoding is valid on most web servers. Integer values between 0-65535 are encoded in a UTF-8 byte sequence that is escaped by percents. The short form is two bytes in length.</p><p>check for three types of errors:</p><div class="itemizedlist"><ul type="disc"><li><p>Not enough bytes. UTF-8 supports two, three, four, five, and six byte encodings. ModSecurity will locate cases when a byte or more is missing.</p></li><li><p>Invalid encoding. The two most significant bits in most characters are supposed to be fixed to 0x80. Attackers can use this to subvert Unicode decoders.</p></li><li><p>Overlong characters. ASCII characters are mapped directly into the Unicode space and are thus represented with a single byte. However, most ASCII characters can also be encoded with two, three, four, five, and six characters thus tricking the decoder into thinking that the character is something else (and, presumably, avoiding the security check).</p></li></ul></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11EB3"></a><code class="literal">verifyCC</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> This operator verifies a given regular expression as a potential credit card number. It first matches with a single generic regular expression then runs the resulting match through a Luhn checksum algorithm to further verify it as a potential credit card number.</p><p>Example:</p><pre class="programlisting">SecRule ARGS "<span class="emphasis"><em>@verifyCC \d{13,16}</em></span>" \ "phase:2,sanitiseMatched,log,auditlog,pass,msg:'Potential credit card number'"</pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11EC4"></a><code class="literal">within</code></h3></div></div><div></div></div><p><span class="emphasis"><em>Description:</em></span> This operator is a string comparison and returns true if the input value is found anywhere within the parameter value. Note that this is similar to <code class="literal">@contains</code>, except that the target and match values are reversed. Macro expansion is performed so you may use variable names such as %{TX.1}, etc.</p><p>Example:</p><pre class="programlisting">SecRule REQUEST_METHOD "!<span class="emphasis"><em>@within get,post,head</em></span>" t:lowercase,deny,status:403 SecAction "pass,setvar:'tx.allowed_methods=get,post,head'" SecRule REQUEST_METHOD "!<span class="emphasis"><em>@within %{tx.allowed_methods}</em></span>" t:lowercase,deny,status:403</pre></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="N11EDC"></a>Macro Expansion</h2></div></div><div></div></div><p>Macros allow for using place holders in rules that will be expanded out to their values at runtime. Currently only variable expansion is supported, however more options may be added in future versions of ModSecurity.</p><p>Format:</p><pre class="programlisting">%{VARIABLE} %{COLLECTION.VARIABLE}</pre><p>Macro expansion can be used in actions such as initcol, setsid, setuid, setvar, setenv, logdata. Operators that are evaluated at runtime support expansion and are noted above. Such operators include @beginsWith, @endsWith, @contains, @within and @streq. You cannot use macro expansion for operators that are "compiled" such as @pm, @rx, etc. as these operators have their values fixed at configure time for efficiency.</p><p>Some values you may want to expand include: TX, REMOTE_ADDR, USERID, HIGHEST_SEVERITY, MATCHED_VAR, MATCHED_VAR_NAME, MULTIPART_STRICT_ERROR, RULE, SESSION, USERID, among others.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="N11EEA"></a>Persistant Storage</h2></div></div><div></div></div><p>At this time it is only possible to have three collections in which data is stored persistantly (i.e. data available to multiple requests). These are: <code class="literal">IP</code>, <code class="literal"> SESSION</code> and <code class="literal">USER</code>.</p><p>Every collection contains several built-in variables that are available and are read-only unless otherwise specified:</p><div class="orderedlist"><ol type="1"><li><p><code class="literal">CREATE_TIME</code> - date/time of the creation of the collection.</p></li><li><p><code class="literal">IS_NEW</code> - set to 1 if the collection is new (not yet persisted) otherwise set to 0.</p></li><li><p><code class="literal">KEY</code> - the value of the initcol variable (the client's IP address in the example).</p></li><li><p><code class="literal">LAST_UPDATE_TIME</code> - date/time of the last update to the collection.</p></li><li><p><code class="literal">TIMEOUT</code> - date/time in seconds when the collection will be updated on disk from memory (if no other updates occur). This variable may be set if you wish to specifiy an explicit expiration time (default is 3600 seconds).</p></li><li><p><code class="literal">UPDATE_COUNTER</code> - how many times the collection has been updated since creation.</p></li><li><p><code class="literal">UPDATE_RATE</code> - is the average rate updates per minute since creation.</p></li></ol></div><p>To create a collection to hold session variables (<code class="literal">SESSION</code>) use action <code class="literal">setsid</code>. To create a collection to hold user variables (<code class="literal">USER</code>) use action <code class="literal">setuid</code>. To create a collection to hold client address variables (<code class="literal">IP</code>) use action <code class="literal">initcol</code>.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>ModSecurity implements atomic updates of persistent variables only for integer variables (counters) at this time. Variables are read from storage whenever <code class="literal">initcol</code> is encountered in the rules and persisted at the end of request processing. Counters are adjusted by applying a delta generated by re-reading the persisted data just before being persisted. This keeps counter data consistent even if the counter was modified and persisted by another thread/process during the transaction.</p></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>ModSecurity uses a Berkley Database (SDBM) for persistant storage. This type of database is generally limited to storing a maximum of 1008 bytes per key. This may be a limitation if you are attempting to store a considerable amount of data in variables for a single key. Some of this limitation is planned to be reduced in a future version of ModSecurity.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="N11F4E"></a>Miscellaneous Topics</h2></div></div><div></div></div><p></p><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N11F52"></a>Impedance Mismatch</h3></div></div><div></div></div><p>Web application firewalls have a difficult job trying to make sense of data that passes by, without any knowledge of the application and its business logic. The protection they provide comes from having an independent layer of security on the outside. Because data validation is done twice, security can be increased without having to touch the application. In some cases, however, the fact that everything is done twice brings problems. Problems can arise in the areas where the communication protocols are not well specified, or where either the device or the application do things that are not in the specification. In such cases it may be possible to design payload that will be interpreted in one way by one device and in another by the other device. This problem is better known as Impedance Mismatch. It can be exploited to evade the security devices.</p><p>While we will continue to enhance ModSecurity to deal with various evasion techniques the problem can only be minimized, but never solved. With so many different application backend chances are some will always do something completely unexpected. The only solution is to be aware of the technologies in the backend when writing rules, adapting the rules to remove the mismatch. See the next section for some examples.</p><div class="section" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="N11F59"></a>PHP Peculiarities for ModSecurity Users</h4></div></div><div></div></div><p>When writing rules to protect PHP applications you need to pay attention to the following facts:</p><div class="orderedlist"><ol type="1"><li><p>When "register_globals" is set to "On" request parameters are automatically converted to script variables. In some PHP versions it is even possible to override the $GLOBALS array.</p></li><li><p>Whitespace at the beginning of parameter names is ignored. (This is very dangerous if you are writing rules to target specific named variables.)</p></li><li><p>The remaining whitespace (in parameter names) is converted to underscores. The same applies to dots and to a "[" if the variable name does not contain a matching closing bracket. (Meaning that if you want to exploit a script through a variable that contains an underscore in the name you can send a parameter with a whitespace or a dot instead.)</p></li><li><p>Cookies can be treated as request parameters.</p></li><li><p>The discussion about variable names applies equally to the cookie names.</p></li><li><p>The order in which parameters are taken from the request and the environment is EGPCS (environment, GET, POST, Cookies, built-in variables). This means that a POST parameter will overwrite the parameters transported on the request line (in QUERY_STRING).</p></li><li><p>When "magic_quotes_gpc" is set to "On" PHP will use backslash to escape the following characters: single quote, double quote, backslash, and the nul byte.</p></li><li><p>If "magic_quotes_sybase" is set to "On" only the single quote will be escaped using another single quote. In this case the "magic_quotes_gpc" setting becomes irrelevant. The "magic_quotes_sybase" setting completely overrides the "magic_quotes_gpc" behaviour but "magic_quotes_gpc" still must be set to "On" for the Sybase-specific quoting to be work.</p></li><li><p>PHP will also automatically create nested arrays for you. For example "p[x][y]=1" results in a total of three variables.</p></li></ol></div></div></div></div></div><div align="center" class="copyright">Copyright (C) 2004-2010 <a href="http://www.breach.com">Breach Security</a></div></body></html>