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<?xml version="1.0" encoding="ISO-8859-1"?>
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<title>Using mod_rewrite to control access - Apache HTTP Server</title>
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<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p>
<p class="apache">Apache HTTP Server Version 2.3</p>
<img alt="" src="../images/feather.gif" /></div>
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<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>
<a href="../mod/mod_rewrite.html">reference documentation</a>. It describes
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>
<li><img alt="" src="../images/down.gif" /> <a href="#blocking-of-robots">Blocking of Robots</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#host-deny">Denying Hosts in a Blacklist</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#referer-deflector">Referer-based Deflector</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><li><a href="remapping.html">Redirection and remapping</a></li><li><a href="vhosts.html">Virtual hosts</a></li><li><a href="proxy.html">Proxying</a></li><li><a href="rewritemap.html">Using RewriteMap</a></li><li><a href="advanced.html">Advanced techniques</a></li><li><a href="avoid.html">When not to use mod_rewrite</a></li></ul></div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></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,
we assume that our site is <code>www.example.com</code>.</p>
<div class="example"><p><code>
RewriteCond %{HTTP_REFERER} <strong>!^$</strong><br />
RewriteCond %{HTTP_REFERER} !www.example.com [NC]<br />
RewriteRule <strong>\.(gif|jpg|png)$</strong> - [F,NC]
</code></p></div>
<p>In this second example, instead of failing the request, we display
an alternate image instead.</p>
<div class="example"><p><code>
RewriteCond %{HTTP_REFERER} <strong>!^$</strong><br />
RewriteCond %{HTTP_REFERER} !www.example.com [NC]<br />
RewriteRule <strong>\.(gif|jpg|png)$</strong> /images/go-away.png [R,NC]
</code></p></div>
<p>In the third example, we redirect the request to an image on some
other site.</p>
<div class="example"><p><code>
RewriteCond %{HTTP_REFERER} <strong>!^$</strong><br />
RewriteCond %{HTTP_REFERER} !www.example.com [NC]<br />
RewriteRule <strong>\.(gif|jpg|png)$</strong> http://other.example.com/image.gif [R,NC]
</code></p></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><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<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,
<code>/robots.txt</code> that specifies those portions of your
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
<code>/secret/files</code>. You may also specify an IP address
range, if you are trying to block that user agent only from the
particular source.</p>
<div class="example"><p><code>
RewriteCond %{HTTP_USER_AGENT} ^<strong>NameOfBadRobot</strong><br />
RewriteCond %{REMOTE_ADDR} =<strong>123\.45\.67\.[8-9]</strong><br />
RewriteRule ^<strong>/secret/files/</strong> - [<strong>F</strong>]
</code></p></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 />
<Location /secret/files><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 class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="host-deny" id="host-deny">Denying Hosts in a Blacklist</a></h2>
<dl>
<dt>Description:</dt>
<dd>
<p>We wish to maintain a blacklist of hosts, rather like
<code>hosts.deny</code>, and have those hosts blocked from
accessing our server.</p>
</dd>
<dt>Solution:</dt>
<dd>
<div class="example"><p><code>
RewriteEngine on<br />
RewriteMap hosts-deny txt:/path/to/hosts.deny<br />
RewriteCond ${hosts-deny:%{REMOTE_ADDR}|NOT-FOUND} !=NOT-FOUND [OR]<br />
RewriteCond ${hosts-deny:%{REMOTE_HOST}|NOT-FOUND} !=NOT-FOUND<br />
RewriteRule ^ - [F]
</code></p></div>
<div class="example"><p><code>
##<br />
## hosts.deny<br />
##<br />
## ATTENTION! This is a map, not a list, even when we treat it as such.<br />
## mod_rewrite parses it for key/value pairs, so at least a<br />
## dummy value "-" must be present for each entry.<br />
##<br />
<br />
193.102.180.41 -<br />
bsdti1.sdm.de -<br />
192.76.162.40 -<br />
</code></p></div>
</dd>
<dt>Discussion:</dt>
<dd>
<p>
The second RewriteCond assumes that you have HostNameLookups turned
on, so that client IP addresses will be resolved. If that's not the
case, you should drop the second RewriteCond, and drop the
<code>[OR]</code> flag from the first RewriteCond.
</p>
</dd>
</dl>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="referer-deflector" id="referer-deflector">Referer-based Deflector</a></h2>
<dl>
<dt>Description:</dt>
<dd>
<p>Redirect requests based on the Referer from which the request
came, with different targets per Referer.</p>
</dd>
<dt>Solution:</dt>
<dd>
<p>The following ruleset uses a map file to associate each Referer
with a redirection target.</p>
<div class="example"><p><code>
RewriteMap deflector txt:/path/to/deflector.map<br />
<br />
RewriteCond %{HTTP_REFERER} !=""<br />
RewriteCond ${deflector:%{HTTP_REFERER}} =-<br />
RewriteRule ^ %{HTTP_REFERER} [R,L]<br />
<br />
RewriteCond %{HTTP_REFERER} !=""<br />
RewriteCond ${deflector:%{HTTP_REFERER}|NOT-FOUND} !=NOT-FOUND<br />
RewriteRule ^ ${deflector:%{HTTP_REFERER}} [R,L]
</code></p></div>
<p>The map file lists redirection targets for each referer, or, if
we just wish to redirect back to where they came from, a "-" is
placed in the map:</p>
<div class="example"><p><code>
##<br />
## deflector.map<br />
##<br />
<br />
http://badguys.example.com/bad/index.html -<br />
http://badguys.example.com/bad/index2.html -<br />
http://badguys.example.com/bad/index3.html http://somewhere.example.com/
</code></p></div>
</dd>
</dl>
</div></div>
<div class="bottomlang">
<p><span>Available Languages: </span><a href="../en/rewrite/access.html" title="English"> en </a></p>
</div><div id="footer">
<p class="apache">Copyright 2011 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
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