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<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>

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