<html><head><META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Processing Phases</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="index.html" title="ModSecurity® Reference
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Manual"><link rel="prev" href="configuration-directives.html" title="Configuration Directives"><link rel="next" href="variables.html" title="Variables"></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 id="navheader"><table summary="Navigation header" width="100%"><tr><th align="center" colspan="3">Processing Phases</th></tr><tr><td align="left" width="20%"><a accesskey="p" href="configuration-directives.html">Prev</a> </td><td align="center" width="60%"> <a accesskey="h" href="index.html">Home</a></td><td align="right" width="20%"> <a accesskey="n" href="variables.html">Next</a></td></tr></table><hr size="1"></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 id="navfooter"><hr size="1"><table summary="Navigation footer" width="100%"><tr><td align="left" width="40%"><a accesskey="p" href="configuration-directives.html">Prev</a> </td><td align="center" width="20%"> </td><td align="right" width="40%"> <a accesskey="n" href="variables.html">Next</a></td></tr><tr><td valign="top" align="left" width="40%">Configuration Directives </td><td align="center" width="20%"><a accesskey="h" href="index.html">Home</a></td><td valign="top" align="right" width="40%"> Variables</td></tr></table></div><div align="center" class="copyright">Copyright (C) 2004-2010 <a href="http://www.breach.com">Breach Security</a></div></body></html>
