1 <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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4 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
5 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
6 action either directly in the rule or in using the
7 <code class="literal">SecDefaultAction</code> directive:</p><pre class="programlisting">SecDefaultAction "log,pass,<span class="emphasis"><em>phase:2</em></span>"
8 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
9 if two rules are adjacent in a configuration file, but are set to
10 execute in different phases, they would not happen one after the other.
11 The order of rules in the configuration file is important only within
12 the rules of each phase. This is especially important when using the
13 <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
14 the end of each transaction no matter what happened in the previous
15 phases. This means it will be processed even if the request was
16 intercepted or the <code class="literal">allow</code> action was used to pass the
17 transaction through.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10D73"></a>Phase Request Headers</h3></div></div><div></div></div><p>Rules in this phase are processed immediately after Apache
18 completes reading the request headers (post-read-request phase). At this
19 point the request body has not been read yet, meaning not all request
20 arguments are available. Rules should be placed in this phase if you
21 need to have them run early (before Apache does something with the
22 request), to do something before the request body has been read,
23 determine whether or not the request body should be buffered, or decide
24 how you want the request body to be processed (e.g. whether to parse it
25 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
26 (Directory, Location, LocationMatch, etc...) as the post-read-request
27 hook does not have this information yet. The exception here is the
28 VirtualHost directive. If you want to use ModSecurity rules inside
29 Apache locations, then they should run in Phase 2. Refer to the Apache
30 Request Cycle/ModSecurity Processing Phases diagram.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10D7D"></a>Phase Request Body</h3></div></div><div></div></div><p>This is the general-purpose input analysis phase. Most of the
31 application-oriented rules should go here. In this phase you are
32 guaranteed to have received the request arguments (provided the request
33 body has been read). ModSecurity supports three encoding types for the
34 request body phase:</p><div class="itemizedlist"><ul type="disc"><li><p><code class="literal">application/x-www-form-urlencoded</code> - used to
35 transfer form data</p></li><li><p><code class="literal">multipart/form-data</code> - used for file
36 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="N10D97"></a>Phase Response Headers</h3></div></div><div></div></div><p>This phase takes place just before response headers are sent back
37 to the client. Run here if you want to observe the response before that
38 happens, and if you want to use the response headers to determine if you
39 want to buffer the response body. Note that some response status codes
40 (such as 404) are handled earlier in the request cycle by Apache and my
41 not be able to be triggered as expected. Additionally, there are some
42 response headers that are added by Apache at a later hook (such as Date,
43 Server and Connection) that we would not be able to trigger on or
44 sanitize. This should work appropriately in a proxy setup or within
45 phase:5 (logging).</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10D9C"></a>Phase Response Body</h3></div></div><div></div></div><p>This is the general-purpose output analysis phase. At this point
46 you can run rules against the response body (provided it was buffered,
47 of course). This is the phase where you would want to inspect the
48 outbound HTML for information disclosure, error messages or failed
49 authentication text.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="N10DA1"></a>Phase Logging</h3></div></div><div></div></div><p>This phase is run just before logging takes place. The rules
50 placed into this phase can only affect how the logging is performed.
51 This phase can be used to inspect the error messages logged by Apache.
52 You cannot deny/block connections in this phase as it is too late. This
53 phase also allows for inspection of other response headers that weren't
54 available during phase:3 or phase:4. Note that you must be careful not
55 to inherit a disruptive action into a rule in this phase as this is a
56 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) 2004-2009 <a href="http://www.breach.com">Breach Security</a></div></body></html>