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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><A NAME="serverroot">Permissions on ServerRoot Directories</A></H2>
 <P>In typical operation, Apache is started by the root
 user, and it switches to the user defined by the <A
 HREF="../mod/core.html#user"><STRONG>User</STRONG></A> directive to serve hits.
 As is the case with any command that root executes, you must take care
 that it is protected from modification by non-root users.  Not only
 must the files themselves be writeable only by root, but so must the
 directories, and parents of all directories.  For example, if you
 choose to place ServerRoot in <CODE>/usr/local/apache</CODE> then it is
 suggested that you create that directory as root, with commands
 like these:

 <BLOCKQUOTE><PRE>
     mkdir /usr/local/apache
     cd /usr/local/apache
     mkdir bin conf logs
     chown 0 . bin conf logs
     chgrp 0 . bin conf logs
     chmod 755 . bin conf logs
 </PRE></BLOCKQUOTE>

 It is assumed that /, /usr, and /usr/local are only modifiable by root.
 When you install the httpd executable, you should ensure that it is
 similarly protected:

 <BLOCKQUOTE><PRE>
     cp httpd /usr/local/apache/bin
     chown 0 /usr/local/apache/bin/httpd
     chgrp 0 /usr/local/apache/bin/httpd
     chmod 511 /usr/local/apache/bin/httpd
 </PRE></BLOCKQUOTE>

 <P>You can create an htdocs subdirectory which is modifiable by other
 users -- since root never executes any files out of there, and shouldn't
 be creating files in there.

 <P>If you allow non-root users to modify any files that root either
 executes or writes on then you open your system to root compromises.
 For example, someone could replace the httpd binary so that the next
 time you start it, it will execute some arbitrary code.  If the logs
 directory is writeable (by a non-root user), someone
 could replace a log file with a symlink to some other system file,
 and then root might overwrite that file with arbitrary data.  If the
 log files themselves are writeable (by a non-root user), then someone
 may be able to overwrite the log itself with bogus data.
 <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 <STRONG>CGI</STRONG> 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 <STRONG>CGI</STRONG> 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 <EM>e.g.</EM>
 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.
 If you are using Apache 1.3 or above, we strongly recommend that you
 include the following line in your server configuration files:
 </P>
 <DL>
  <DD><SAMP>UserDir&nbsp;disabled&nbsp;root</SAMP>
  </DD>
 </DL>

 <HR>
 <P>Please send any other useful security tips to The Apache Group
 by filling out a
 <A HREF="http://www.apache.org/bug_report.html">problem report</A>.
 If you are confident you have found a security bug in the Apache
 source code itself, <A
 HREF="http://www.apache.org/security_report.html">please let us
 know</A>.

 <P>
 <HR>

 <!--#include virtual="footer.html" -->
 </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><A NAME="serverroot">Permissions on ServerRoot Directories</A></H2>
	<P>In typical operation, Apache is started by the root
	user, and it switches to the user defined by the <A
	HREF="../mod/core.html#user"><STRONG>User</STRONG></A> directive to serve hits.
	As is the case with any command that root executes, you must take care
	that it is protected from modification by non-root users. Not only
	must the files themselves be writeable only by root, but so must the
	directories, and parents of all directories. For example, if you
	choose to place ServerRoot in <CODE>/usr/local/apache</CODE> then it is
	suggested that you create that directory as root, with commands
	like these:

	<BLOCKQUOTE><PRE>
	mkdir /usr/local/apache
	cd /usr/local/apache
	mkdir bin conf logs
	chown 0 . bin conf logs
	chgrp 0 . bin conf logs
	chmod 755 . bin conf logs
	</PRE></BLOCKQUOTE>

	It is assumed that /, /usr, and /usr/local are only modifiable by root.
	When you install the httpd executable, you should ensure that it is
	similarly protected:

	<BLOCKQUOTE><PRE>
	cp httpd /usr/local/apache/bin
	chown 0 /usr/local/apache/bin/httpd
	chgrp 0 /usr/local/apache/bin/httpd
	chmod 511 /usr/local/apache/bin/httpd
	</PRE></BLOCKQUOTE>

	<P>You can create an htdocs subdirectory which is modifiable by other
	users -- since root never executes any files out of there, and shouldn't
	be creating files in there.

	<P>If you allow non-root users to modify any files that root either
	executes or writes on then you open your system to root compromises.
	For example, someone could replace the httpd binary so that the next
	time you start it, it will execute some arbitrary code. If the logs
	directory is writeable (by a non-root user), someone
	could replace a log file with a symlink to some other system file,
	and then root might overwrite that file with arbitrary data. If the
	log files themselves are writeable (by a non-root user), then someone
	may be able to overwrite the log itself with bogus data.
	<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 <STRONG>CGI</STRONG> 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 <STRONG>CGI</STRONG> 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 <EM>e.g.</EM>
	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.
	If you are using Apache 1.3 or above, we strongly recommend that you
	include the following line in your server configuration files:
	</P>
	<DL>
	<DD><SAMP>UserDir disabled root</SAMP>
	</DD>
	</DL>

	<HR>
	<P>Please send any other useful security tips to The Apache Group
	by filling out a
	<A HREF="http://www.apache.org/bug_report.html">problem report</A>.
	If you are confident you have found a security bug in the Apache
	source code itself, <A
	HREF="http://www.apache.org/security_report.html">please let us
	know</A>.

	<P>
	<HR>

	<!--#include virtual="footer.html" -->
	</BODY>
	</HTML>