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<H1 ALIGN="CENTER">Security Tips for Server Configuration</H1>

<hr>

<P>Some hints and tips on security issues in setting up a web server. Some of
the suggestions will be general, others specific to Apache.

<HR>

<H2>Permissions on Log File Directories</H2>
<P>When Apache starts, it opens the log files as the user who started the
server before switching to the user defined in the 
<a href="../mod/core.html#user"><b>User</b></a> directive.  Anyone who
has write permission for the directory where any log files are
being written to can append pseudo-arbitrary data to any file on the
system which is writable by the user who starts Apache.  Since the
server is normally started by root, you should <EM>NOT</EM> give anyone
write permission to the directory where logs are stored unless you
want them to have root access. 
<P>
<HR>
<H2>Server Side Includes</H2>
<P>Server side includes (SSI) can be configured so that users can execute
arbitrary programs on the server. That thought alone should send a shiver
down the spine of any sys-admin.<p>

One solution is to disable that part of SSI. To do that you use the
IncludesNOEXEC option to the <A HREF="../mod/core.html#options">Options</A>
directive.<p>

<HR>

<H2>Non Script Aliased CGI</H2>
<P>Allowing users to execute <B>CGI</B> scripts in any directory should only
be considered if;
<OL>
 <LI>You trust your users not to write scripts which will deliberately or
accidentally expose your system to an attack.
 <LI>You consider security at your site to be so feeble in other areas, as to
make one more potential hole irrelevant.
 <LI>You have no users, and nobody ever visits your server.
</OL><p>
<HR>

<H2>Script Alias'ed CGI</H2>
<P>Limiting <B>CGI</B> to special directories gives the admin control over
what goes into those directories. This is inevitably more secure than
non script aliased CGI, but <strong>only if users with write access to the
directories are trusted</strong> or the admin is willing to test each new CGI
script/program for potential security holes.<P>

Most sites choose this option over the non script aliased CGI approach.<p>

<HR>
<H2>CGI in general</H2>
<P>Always remember that you must trust the writers of the CGI script/programs
or your ability to spot potential security holes in CGI, whether they were
deliberate or accidental.<p>

All the CGI scripts will run as the same user, so they have potential to
conflict (accidentally or deliberately) with other scripts e.g.
User A hates User B, so he writes a script to trash User B's CGI
database.  One program which can be used to allow scripts to run
as different users is <A HREF="../suexec.html">suEXEC</A> which is
included with Apache as of 1.2 and is called from special hooks in
the Apache server code.  Another popular way of doing this is with
<A HREF="http://wwwcgi.umr.edu/~cgiwrap/">CGIWrap</A>.  <P>

<HR>


<H2>Stopping users overriding system wide settings...</H2>
<P>To run a really tight ship, you'll want to stop users from setting
up <CODE>.htaccess</CODE> files which can override security features
you've configured. Here's one way to do it...<p>

In the server configuration file, put
<blockquote><code>
&lt;Directory /&gt; <br>
AllowOverride None <br>
Options None <br>
allow from all <br>
&lt;/Directory&gt; <br>
</code></blockquote>

Then setup for specific directories<P>

This stops all overrides, Includes and accesses in all directories apart
from those named.<p>
<HR>
<H2>
 Protect server files by default
</H2>
<P>
One aspect of Apache which is occasionally misunderstood is the feature
of default access.  That is, unless you take steps to change it, if the
server can find its way to a file through normal URL mapping rules, it
can serve it to clients.
</P>
<P>
For instance, consider the following example:
</P>
<OL>
 <LI><SAMP># cd /; ln -s / public_html</SAMP>
 </LI>
 <LI>Accessing <SAMP>http://localhost/~root/</SAMP>
 </LI>
</OL>
<P>
This would allow clients to walk through the entire filesystem.  To work
around this, add the following block to your server's configuration:
</P>
<PRE>
 &lt;Directory /&gt;
     Order deny,allow
     Deny from all
 &lt;/Directory&gt;
</PRE>
<P>
This will forbid default access to filesystem locations.  Add
appropriate
<A
 HREF="../mod/core.html#directory"
><SAMP>&lt;Directory&gt;</SAMP></A>
blocks to allow access only
in those areas you wish.  For example,
</P>
<PRE>
 &lt;Directory /usr/users/*/public_html&gt;
     Order deny,allow
     Allow from all
 &lt;/Directory&gt;
 &lt;Directory /usr/local/httpd&gt;
     Order deny,allow
     Allow from all
 &lt;/Directory&gt;
</PRE>
<P>
Pay particular attention to the interactions of
<A
 HREF="../mod/core.html#location"
><SAMP>&lt;Location&gt;</SAMP></A>
and
<A
 HREF="../mod/core.html#directory"
><SAMP>&lt;Directory&gt;</SAMP></A>
directives; for instance, even if <SAMP>&lt;Directory /&gt;</SAMP>
denies access, a <SAMP>&lt;Location /&gt;</SAMP> directive might
overturn it.
</P>
<P>
Also be wary of playing games with the
<A
 HREF="../mod/mod_userdir.html#userdir"
>UserDir</A>
directive; setting it to something like <SAMP>&quot;./&quot;</SAMP>
would have the same effect, for root, as the first example above.

<HR>
<P>Please send any other useful security tips to The Apache Group
by filling out a
<A HREF="http://www.apache.org/bugdb.cgi">problem report</A>, or by
sending mail to
<A HREF="mailto:apache-bugs@mail.apache.org">apache-bugs@mail.apache.org</A>
<p>
<HR>

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