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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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 </BODY>
 </HTML>
	<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
	<HTML>
	<HEAD>
	<TITLE>Apache HTTP Server: Security Tips</TITLE>
	</HEAD>

	<!-- Background white, links blue (unvisited), navy (visited), red (active) -->
	<BODY
	BGCOLOR="#FFFFFF"
	TEXT="#000000"
	LINK="#0000FF"
	VLINK="#000080"
	ALINK="#FF0000"
	>
	<!--#include virtual="header.html" -->
	<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>
	<Directory /> <br>
	AllowOverride None <br>
	Options None <br>
	allow from all <br>
	</Directory> <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>
	<Directory />
	Order deny,allow
	Deny from all
	</Directory>
	</PRE>
	<P>
	This will forbid default access to filesystem locations. Add
	appropriate
	<A
	HREF="../mod/core.html#directory"
	><SAMP><Directory></SAMP></A>
	blocks to allow access only
	in those areas you wish. For example,
	</P>
	<PRE>
	<Directory /usr/users/*/public_html>
	Order deny,allow
	Allow from all
	</Directory>
	<Directory /usr/local/httpd>
	Order deny,allow
	Allow from all
	</Directory>
	</PRE>
	<P>
	Pay particular attention to the interactions of
	<A
	HREF="../mod/core.html#location"
	><SAMP><Location></SAMP></A>
	and
	<A
	HREF="../mod/core.html#directory"
	><SAMP><Directory></SAMP></A>
	directives; for instance, even if <SAMP><Directory /></SAMP>
	denies access, a <SAMP><Location /></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>"./"</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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