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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>5. PowerDNS Security Advisory 2006-01: Malformed TCP queries can lead to a buffer overflow which might be exploitable</title><link rel="stylesheet" href="docbook.css" type="text/css" /><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="PowerDNS manual" /><link rel="up" href="powerdns.html" title="Chapter 1. The PowerDNS dynamic nameserver" /><link rel="prev" href="security-policy.html" title="4. Security" /><link rel="next" href="powerdns-advisory-2006-02.html" title="6. PowerDNS Security Advisory 2006-02: Zero second CNAME TTLs can make PowerDNS exhaust allocated stack space, and crash" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">5. PowerDNS Security Advisory 2006-01: Malformed TCP queries can lead to a buffer overflow which might be exploitable</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="security-policy.html">Prev</a> </td><th width="60%" align="center">Chapter 1. The PowerDNS dynamic nameserver</th><td width="20%" align="right"> <a accesskey="n" href="powerdns-advisory-2006-02.html">Next</a></td></tr></table><hr /></div><div class="sect1" title="5. PowerDNS Security Advisory 2006-01: Malformed TCP queries can lead to a buffer overflow which might be exploitable"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="powerdns-advisory-2006-01"></a>5. PowerDNS Security Advisory 2006-01: Malformed TCP queries can lead to a buffer overflow which might be exploitable</h2></div></div></div><p>
</p><div class="table"><a id="idp7588800"></a><p class="title"><b>Table 1.1. PowerDNS Security Advisory</b></p><div class="table-contents"><table summary="PowerDNS Security Advisory" border="1"><colgroup><col /><col /></colgroup><tbody><tr><td>
CVE
</td><td>
CVE-2006-4251
</td></tr><tr><td>
Date
</td><td>
13th of November 2006
</td></tr><tr><td>
Affects
</td><td>
PowerDNS Recursor versions 3.1.3 and earlier, on all operating systems.
</td></tr><tr><td>
Not affected
</td><td>
No versions of the PowerDNS Authoritative Server ('pdns_server') are affected.
</td></tr><tr><td>
Severity
</td><td>
Critical
</td></tr><tr><td>
Impact
</td><td>
Potential remote system compromise.
</td></tr><tr><td>
Exploit
</td><td>
As far as we know, no exploit is available as of 11th of November 2006.
</td></tr><tr><td>
Solution
</td><td>
Upgrade to PowerDNS Recursor 3.1.4, or apply the patches referred below and recompile
</td></tr><tr><td>
Workaround
</td><td>
Disable TCP access to the Recursor. This will have slight operational impact, but it is likely that this will not lead
to meaningful degradation of service. Disabling access is best performed at packet level, either by configuring a firewall, or
instructing the host operating system to drop TCP connections to port 53.
Additionally, exposure can be limited by configuring the <span class="command"><strong>allow-from</strong></span> setting so only trusted users
can query your nameserver.
</td></tr></tbody></table></div></div><p><br class="table-break" />
</p><p>
PowerDNS Recursor 3.1.3 and previous miscalculate the length of incoming TCP DNS queries, and will attempt to read up to 4 gigabytes of query
into a 65535 byte buffer.
</p><p>
We have not verified if this problem might actually lead to a system compromise, but are acting on the assumption that it might.
</p><p>
For distributors, a minimal patch is available on <a class="ulink" href="http://wiki.powerdns.com/cgi-bin/trac.fcgi/changeset/915" target="_top">the PowerDNS wiki</a>.
Additionally, those shipping very old versions of the PowerDNS Recursor might benefit from this <a class="ulink" href="http://ds9a.nl/tmp/cve-2006-4251.patch" target="_top">
patch</a>.
</p><p>
The impact of these and other security problems can be lessened by considering the advice in <a class="xref" href="security.html" title="Chapter 7. Security settings & considerations">Chapter 7, <i>Security settings & considerations</i></a>.
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