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<!DOCTYPE document [
  <!ENTITY project SYSTEM "project.xml">
]>
<document url="cgi-howto.html">

    &project;

    <properties>
        <title>CGI How To</title>
    </properties>

<body>

<section name="Table of Contents">
<toc/>
</section>

<section name="Introduction">

<p>The CGI (Common Gateway Interface) defines a way for a web server to
interact with external content-generating programs, which are often
referred to as CGI programs or CGI scripts.
</p>

<p>Within Tomcat, CGI support can be added when you are using Tomcat as your
HTTP server and require CGI support.  Typically this is done
during development when you don't want to run a web server like
Apache httpd.
Tomcat's CGI support is largely compatible with Apache httpd's,
but there are some limitations (e.g., only one cgi-bin directory).
</p>

<p>CGI support is implemented using the servlet class
<code>org.apache.catalina.servlets.CGIServlet</code>.  Traditionally,
this servlet is mapped to the URL pattern "/cgi-bin/*".</p>

<p>By default CGI support is disabled in Tomcat.</p>
</section>

<section name="Installation">

<p><strong>CAUTION</strong> - CGI scripts are used to execute programs
external to the Tomcat JVM. If you are using the Java SecurityManager this
will bypass your security policy configuration in <code>catalina.policy.</code></p>

<p>To enable CGI support:</p>

<ol>
<li><p>There are commented-out sample servlet and servlet-mapping elements for
CGI servlet in the default <code>$CATALINA_BASE/conf/web.xml</code> file.
To enable CGI support in your web application, copy that servlet and
servlet-mapping declarations into <code>WEB-INF/web.xml</code> file of your
web application.</p>

<p>Uncommenting the servlet and servlet-mapping in
<code>$CATALINA_BASE/conf/web.xml</code> file enables CGI for all installed
web applications at once.</p>
</li>

<li><p>Set <code>privileged="true"</code> on the Context element for your
web application.</p>

<p>Only Contexts which are marked as privileged are allowed to use the
CGI servlet. Note that modifying the global <code>$CATALINA_BASE/conf/context.xml</code>
file affects all web applications. See
<a href="config/context.html">Context documentation</a> for details.</p>
</li>
</ol>

</section>

<section name="Configuration">

<p>There are several servlet init parameters which can be used to
configure the behaviour of the CGI servlet.</p>
<ul>
<li><strong>cgiPathPrefix</strong> - The CGI search path will start at
the web application root directory + File.separator + this prefix.
By default there is no value, which results in the web application root
directory being used as the search path. The recommended value is
<code>WEB-INF/cgi</code></li>
<li><strong>debug</strong> - Debugging detail level for messages logged
by this servlet. Useful values range from 0 to 5 where 0 means no logging and 5
means maximum logging. Values of 10 or more mean maximum logging plus debug info
added to the HTTP response. If an error occurs and debug is 10 or more the
standard error page mechanism will be disabled and a response body with debug
information will be produced. The debug page is not considered secure and should
not be enabled for production systems. Note that any value of 10 or more has the
same effect as a value of 10. Default is <code>0</code>.</li>
<li><strong>cmdLineArgumentsDecoded</strong> - If command line argumemnts
are enabled (via <strong>enableCmdLineArguments</strong>) and Tomcat is running
on Windows then each individual decoded command line argument must match this
pattern else the request will be rejected. This is to protect against known
issues passing command line arguments from Java to Windows. These issues can
lead to remote code execution. For more information on these issues see
<a href="https://codewhitesec.blogspot.com/2016/02/java-and-command-line-injections-in-windows.html">Markus
Wulftange&apos;s blog</a> and this archived
<a href="https://web.archive.org/web/20161228144344/https://blogs.msdn.microsoft.com/twistylittlepassagesallalike/2011/04/23/everyone-quotes-command-line-arguments-the-wrong-way/">blog
by Daniel Colascione</a>.</li>
<li><strong>executable</strong> - The of the executable to be used to
run the script. You may explicitly set this parameter to be an empty string
if your script is itself executable (e.g. an exe file). Default is
<code>perl</code>.</li>
<li><strong>executable-arg-1</strong>, <strong>executable-arg-2</strong>,
and so on - additional arguments for the executable. These precede the
CGI script name. By default there are no additional arguments.</li>
<li><strong>envHttpHeaders</strong> - A regular expression used to select the
HTTP headers passed to the CGI process as environment variables. Note that
headers are converted to upper case before matching and that the entire header
name must match the pattern. Default is
<code>ACCEPT[-0-9A-Z]*|CACHE-CONTROL|COOKIE|HOST|IF-[-0-9A-Z]*|REFERER|USER-AGENT</code>
</li>
<li><strong>parameterEncoding</strong> - Name of the parameter encoding
to be used with the CGI servlet. Default is
<code>System.getProperty("file.encoding","UTF-8")</code>. That is the system
default encoding, or UTF-8 if that system property is not available.</li>
<li><strong>passShellEnvironment</strong> - Should the shell environment
variables from Tomcat process (if any) be passed to the CGI script? Default is
<code>false</code>.</li>
<li><strong>stderrTimeout</strong> - The time (in milliseconds) to wait for
the reading of stderr to complete before terminating the CGI process. Default
is <code>2000</code>.</li>
</ul>


</section>

</body>

</document>
