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<title>Using mod_rewrite to control access - Apache HTTP Server</title>
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<p class="apache">Apache HTTP Server Version 2.3</p>
<div id="path">
<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.3</a> > <a href="./">Rewrite</a></div><div id="page-content"><div id="preamble"><h1>Using mod_rewrite to control access</h1>
<div class="toplang">
<p><span>Available Languages: </span><a href="/en/rewrite/access.html" title="English"> en </a></p>
</div>
<p>This document supplements the <code class="module"><a href="/mod/mod_rewrite.html">mod_rewrite</a></code>
how you can use <code class="module"><a href="/mod/mod_rewrite.html">mod_rewrite</a></code> to control access to
various resources, and other related techniques.
This includes many examples of common uses of mod_rewrite,
including detailed descriptions of how each works.</p>
<div class="warning">Note that many of these examples won't work unchanged in your
particular server configuration, so it's important that you understand
them, rather than merely cutting and pasting the examples into your
configuration.</div>
</div>
<div id="quickview"><ul id="toc"><li><img alt="" src="/images/down.gif" /> <a href="#blocked-inline-images">Forbidding Image "Hotlinking"</a></li>
</ul><h3>See also</h3><ul class="seealso"><li><a href="/mod/mod_rewrite.html">Module documentation</a></li><li><a href="intro.html">mod_rewrite introduction</a></li></ul></div>
<div class="section">
<h2><a name="blocked-inline-images" id="blocked-inline-images">Forbidding Image "Hotlinking"</a></h2>
<dl>
<dt>Description:</dt>
<dd>
<p>The following technique forbids the practice of other sites
including your images inline in their pages. This practice is
often referred to as "hotlinking", and results in
your bandwidth being used to serve content for someone else's
site.</p>
</dd>
<dt>Solution:</dt>
<dd>
<p>This technique relies on the value of the
<code>HTTP_REFERER</code> variable, which is optional. As
such, it's possible for some people to circumvent this
limitation. However, most users will experience the failed
request, which should, over time, result in the image being
removed from that other site.</p>
<p>There are several ways that you can handle this
situation.</p>
<p>In this first example, we simply deny the request, if it didn't
initiate from a page on our site. For the purpose of this example,
<div class="example"><pre>
RewriteCond %{HTTP_REFERER} <strong>!^$</strong>
RewriteCond %{HTTP_REFERER} !www.example.com [NC]
RewriteRule <strong>\.(gif|jpg|png)$</strong> - [F,NC]
</pre></div>
<p>In this second example, instead of failing the request, we display
an alternate image instead.</p>
<div class="example"><pre>
RewriteCond %{HTTP_REFERER} <strong>!^$</strong>
RewriteCond %{HTTP_REFERER} !www.example.com [NC]
</pre></div>
<p>In the third example, we redirect the request to an image on some
third-party site.</p>
<div class="example"><pre>
RewriteCond %{HTTP_REFERER} <strong>!^$</strong>
RewriteCond %{HTTP_REFERER} !www.example.com [NC]
</pre></div>
<p>Of these techniques, the last two tend to be the most effective
in getting people to stop hotlinking your images, because they will
simply not see the image that they expected to see.</p>
</dd>
<dt>Discussion:</dt>
<dd>
<p>If all you wish to do is deny access to the resource, rather
than redirecting that request elsewhere, this can be
accomplished without the use of mod_rewrite:</p>
<div class="example"><p><code>
SetEnvIf Referer example\.com localreferer<br />
<FilesMatch \.(jpg|png|gif)$><br />
Order deny,allow<br />
Deny from all<br />
Allow from env=localreferer<br />
</FilesMatch>
</code></p></div>
</dd>
</dl>
<div class="section">
<h2><a name="blocking-of-robots" id="blocking-of-robots">Blocking of Robots</a></h2>
<dl>
<dt>Description:</dt>
<dd>
<p>
In this recipe, we discuss how to block persistent requests from
a particular robot, or user agent.</p>
<p>The standard for robot exclusion defines a file,
website where you which to exclude robots. However, some robots
do not honor these files.
</p>
<p>Note that there are methods of accomplishing this which do
not use mod_rewrite. Note also that any technique that relies on
the clients <code>USER_AGENT</code> string can be circumvented
very easily, since that string can be changed.</p>
</dd>
<dt>Solution:</dt>
<dd>
<p>We use a ruleset that specifies the directory to be
protected, and the client <code>USER_AGENT</code> that
identifies the malicious or persistent robot.</p>
<p>In this example, we are blocking a robot called
<code>NameOfBadRobot</code> from a location
range, if you are trying to block that user agent only from the
particular source.</p>
<div class="example"><pre>
RewriteCond %{HTTP_USER_AGENT} ^<strong>NameOfBadRobot</strong>
RewriteCond %{REMOTE_ADDR} =<strong>123\.45\.67\.[8-9]</strong>
</pre></div>
</dd>
<dt>Discussion:</dt>
<dd>
<p>
Rather than using mod_rewrite for this, you can accomplish the
same end using alternate means, as illustrated here:
</p>
<div class="example"><p><code>
SetEnvIfNoCase User-Agent ^NameOfBadRobot goaway<br />
Order allow,deny<br />
Allow from all<br />
Deny from env=goaway<br />
</Location>
</code></p></div>
<p>
As noted above, this technique is trivial to circumvent, by simply
modifying the <code>USER_AGENT</code> request header. If you
are experiencing a sustained attack, you should consider blocking
it at a higher level, such as at your firewall.
</p>
</dd>
</dl>
</div></div>
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