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From Allan Liska <al...@allan.org>
Subject [PATCH] security_tips.html
Date Sun, 30 Sep 2001 01:02:51 GMT

I've cleaned up some of the HTML to make it more in line with the
recommendation in the tutorials, and enhanced the section on Server Side
Includes.  If this looks okay, I will start working on some of the other
sections outlined in my earlier proposal.

Please let me know what you think.





Index: httpd-docs-1.3/htdocs/manual/misc/security_tips.html
===================================================================
RCS file: /home/cvspublic/httpd-docs-1.3/htdocs/manual/misc/security_tips.html,v
retrieving revision 1.23
diff -u -r1.23 security_tips.html
--- httpd-docs-1.3/htdocs/manual/misc/security_tips.html	2001/09/24 01:36:41	1.23
+++ httpd-docs-1.3/htdocs/manual/misc/security_tips.html	2001/09/30 01:03:31
@@ -1,64 +1,82 @@
 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
-<HTML>
-<HEAD>
-<TITLE>Apache HTTP Server: Security Tips</TITLE>
-</HEAD>
+<html>
+<head>
+<title>Apache HTTP Server: Security Tips</title>
+<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
+</head>

 <!-- Background white, links blue (unvisited), navy (visited), red (active) -->
-<BODY
- BGCOLOR="#FFFFFF"
- TEXT="#000000"
- LINK="#0000FF"
- VLINK="#000080"
- ALINK="#FF0000"
+<body
+ bgcolor="#FFFFFF"
+ text="#000000"
+ link="#0000FF"
+ vlink="#000080"
+ alink="#FF0000"
 >
 <!--#include virtual="header.html" -->
-<H1 ALIGN="CENTER">Security Tips for Server Configuration</H1>
+<h1 align="center">Security Tips for Server Configuration</h1>

-<HR>
+<ul>
+<li><a href="#serverroot">Permissions on ServerRoot Directories</a></li>

-<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.
+<li><a href="#ssi">Server Side Includes</a>

-<HR>
+<li><a href="#nsaliasedcgi">Non Script Aliased CGI</a></li>

-<H2><A NAME="serverroot">Permissions on ServerRoot Directories</A></H2>
-<P>In typical operation, Apache is started by the root
+<li><a href="#saliasedcgi">Script Aliased CGI</a></li>
+
+<li><a href="#cgi">CGI in General</a></li>
+
+<li><a href="#systemsettings">Protecting System Settings</a></li>
+
+<li><a href="#protectserverfiles">Protect Server Files by Default</a></li>
+</ul>
+
+<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.</p>
+
+<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.
+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
+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>
+<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>
+</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>
+<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>
+</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>You can create an htdocs subdirectory which is modifiable by other
+users -- since root never executes any files within that directort, and
+should not be creating files there.
+</p>

-<P>If you allow non-root users to modify any files that root either
+<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
@@ -67,21 +85,49 @@
 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>
+</p>
+<hr>
+<h2><a name="ssi">Server Side Includes</a></h2>
+<p>Server Side Includes (SSI), present a server administrator with
+several potential security risks.</p>
+
+<p>
+The first risk is the increased load on the server.  All SSI-enabled
+files have to be parsed by Apache, whether or not there are any SSI
+directives included within the file.  While this load increase is
+minor, in a shared server environment it can become significant.</p>
+
+<p>
+SSI files also pose the same risks that are associated with CGI scripts
+in general.  A user can execute any CGI script through an SSI-enabled
+file.  That should definitely give server administrators pause.</p>
+
+<p>
+There are ways to enhance the security of SSI files, while still taking
+advantage of the benefits they provide.</p>
+
+<p>
+To start, never enable SSI for all files with .html or .htm
+extensions.  This is especially true in a shared, or heavily trafficked
+server environment.  SSI-enabled files should have a separate extension,
+such as the conventional .shtml.  Thus keeping server load to a minimum.
+</p>
+
+<p>Another solution is to disable the #exec command withing  SSI. To do
+that you use the IncludesNOEXEC option to the
+<a href="../mod/core.html#options">Options</a> directive.</p>
+
+<blockquote><code>
+&lt;Directory /&gt; <br>
+Options IncludesNOEXEC <br>
+&lt;/Directory&gt; <br>
+</code></blockquote>

-<HR>

-<H2>Non Script Aliased CGI</H2>
-<P>Allowing users to execute <STRONG>CGI</STRONG> scripts in any directory
+<hr>
+
+<h2><a name="nsaliasedcgi">Non Script Aliased CGI</a></h2>
+<p>Allowing users to execute <strong>CGI</strong> scripts in any directory
 should only
 be considered if;
 <OL>
@@ -90,93 +136,94 @@
  <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>
+</OL><p>
+<hr>

-<H2>Script Alias'ed CGI</H2>
-<P>Limiting <STRONG>CGI</STRONG> to special directories gives the admin
+<h2><a name="saliasedcgi">Script Aliased CGI</a></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
+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>
+
+<p>Most sites choose this option over the non script aliased CGI approach.
+</p>
+
+<hr>
+<h2><a name="cgi">CGI in General</a></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>
+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>
+<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
+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>
+<a href="http://wwwcgi.umr.edu/~cgiwrap/">CGIWrap</a>.  </p>

-<HR>
+<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>
+<h2><a name="systemsettings">Protecting System Settings</a></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>
+<blockquote><code>
+&lt;Directory /&gt; <br>
+AllowOverride None <br>
+Options None <br>
+Allow from all <br>
+&lt;/Directory&gt; <br>
+</code></blockquote>
+
+<p>Then setup for specific directories</p>
+
+<p> This stops all overrides, Includes and accesses in all directories apart
+from those named.</p>
+<hr>
+<h2>
+<a name="protectserverfiles">Protect Server Files by Default</a>
+</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>
+</p>
+<p>
 For instance, consider the following example:
-</P>
+</p>
 <OL>
- <LI><SAMP># cd /; ln -s / public_html</SAMP>
+ <LI><samp># cd /; ln -s / public_html</samp>
  </LI>
- <LI>Accessing <SAMP>http://localhost/~root/</SAMP>
+ <LI>Accessing <samp>http://localhost/~root/</samp>
  </LI>
 </OL>
-<P>
+<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>
+</p>
 <PRE>
  &lt;Directory /&gt;
      Order Deny,Allow
      Deny from all
  &lt;/Directory&gt;
 </PRE>
-<P>
+<p>
 This will forbid default access to filesystem locations.  Add
 appropriate
 <A
- HREF="../mod/core.html#directory"
-><SAMP>&lt;Directory&gt;</SAMP></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>
+</p>
 <PRE>
  &lt;Directory /usr/users/*/public_html&gt;
      Order Deny,Allow
@@ -187,45 +234,42 @@
      Allow from all
  &lt;/Directory&gt;
 </PRE>
-<P>
+<p>
 Pay particular attention to the interactions of
 <A
- HREF="../mod/core.html#location"
-><SAMP>&lt;Location&gt;</SAMP></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
+ 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>
+</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>
+<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>
+</p>
 <DL>
- <DD><SAMP>UserDir&nbsp;disabled&nbsp;root</SAMP>
+ <DD><samp>UserDir&nbsp;disabled&nbsp;root</samp>
  </DD>
 </DL>

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

-<P>
+<p>

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


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