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 <H1 ALIGN="CENTER">Apache suEXEC Support</H1>

 <P ALIGN="LEFT">
 <OL>
         <LI><BIG><STRONG>CONTENTS</STRONG></BIG></LI>
         <LI><A HREF="#what">What is suEXEC?</A></LI>
         <LI><A HREF="#before">Before we begin.</A></LI>
         <LI><A HREF="#model">suEXEC Security Model.</A></LI>
         <LI><A HREF="#install">Configuring &amp; Installing suEXEC</A></LI>
         <LI><A HREF="#enable">Enabling &amp; Disabling suEXEC</A></LI>
         <LI><A HREF="#debug">Debugging suEXEC</A></LI>
         <LI><A HREF="#jabberwock">Beware the Jabberwock: Warnings &amp;
          Examples</A></LI>
 </OL>
 </P>

 <H3><A NAME="what">What is suEXEC?</A></H3>
 <P ALIGN="LEFT">
 The <STRONG>suEXEC</STRONG> feature -- introduced in Apache 1.2 -- provides
 Apache users the ability to run <STRONG>CGI</STRONG> and <STRONG>SSI</STRONG>
 programs under user IDs different from the user ID of the calling web-server.
 Normally, when a CGI or SSI program executes, it runs as the same user who is
 running the web server.
 </P>

 <P ALIGN="LEFT">
 Used properly, this feature can reduce considerably the security risks involved
 with allowing users to develop and run private CGI or SSI programs.  However,
 if suEXEC is improperly configured, it can cause any number of problems and
 possibly create new holes in your computer's security.  If you aren't familiar
 with managing setuid root programs and the security issues they present, we
 highly recommend that you not consider using suEXEC.
 </P>

 <P ALIGN="CENTER">
 <STRONG><A HREF="suexec.html">BACK TO CONTENTS</A></STRONG>
 </P>

 <H3><A NAME="before">Before we begin.</A></H3>
 <P ALIGN="LEFT">
 Before jumping head-first into this document, you should be aware of the
 assumptions made on the part of the Apache Group and this document.
 </P>

 <P ALIGN="LEFT">
 First, it is assumed that you are using a UNIX derivate operating system that
 is capable of <STRONG>setuid</STRONG> and <STRONG>setgid</STRONG> operations.
 All command examples are given in this regard.  Other platforms, if they are
 capable of supporting suEXEC, may differ in their configuration.
 </P>

 <P ALIGN="LEFT">
 Second, it is assumed you are familiar with some basic concepts of your
 computer's security and its administration.  This involves an understanding
 of <STRONG>setuid/setgid</STRONG> operations and the various effects they
 may have on your system and its level of security.
 </P>

 <P ALIGN="LEFT">
 Third, it is assumed that you are using an <STRONG>unmodified</STRONG>
 version of suEXEC code.  All code for suEXEC has been carefully scrutinized and
 tested by the developers as well as numerous beta testers.  Every precaution
 has been taken to ensure a simple yet solidly safe base of code.  Altering this
 code can cause unexpected problems and new security risks.  It is
 <STRONG>highly</STRONG> recommended you not alter the suEXEC code unless you
 are well versed in the particulars of security programming and are willing to
 share your work with the Apache Group for consideration.
 </P>

 <P ALIGN="LEFT">
 Fourth, and last, it has been the decision of the Apache Group to
 <STRONG>NOT</STRONG> make suEXEC part of the default installation of Apache.
 To this end, suEXEC configuration requires of the administrator careful
 attention to details.  After due consideration has been given to the various
 settings for suEXEC, the administrator may install suEXEC through normal
 installation methods. The values for these settings need to be carefully
 determined and specified by the administrator to properly maintain system
 security during the use of suEXEC functionality.  It is through this detailed
 process that the Apache Group hopes to limit suEXEC installation only to those
 who are careful and determined enough to use it.
 </P>

 <P ALIGN="LEFT">
 Still with us?  Yes?  Good.  Let's move on!
 </P>

 <P ALIGN="CENTER">
 <STRONG><A HREF="suexec.html">BACK TO CONTENTS</A></STRONG>
 </P>

 <H3><A NAME="model">suEXEC Security Model</A></H3>
 <P ALIGN="LEFT">
 Before we begin configuring and installing suEXEC, we will first discuss
 the security model you are about to implement.  By doing so, you may
 better understand what exactly is going on inside suEXEC and what precautions
 are taken to ensure your system's security.
 </P>

 <P ALIGN="LEFT">
 <STRONG>suEXEC</STRONG> is based on a setuid "wrapper" program that is
 called by the main Apache web server.  This wrapper is called when an HTTP
 request is made for a CGI or SSI program that the administrator has designated
 to run as a userid other than that of the main server.  When such a request
 is made, Apache provides the suEXEC wrapper with the program's name and the
 user and group IDs under which the program is to execute.
 </P>

 <P ALIGN="LEFT">
 The wrapper then employs the following process to determine success or
 failure -- if any one of these conditions fail, the program logs the failure
 and exits with an error, otherwise it will continue:
 <OL>
  <LI><STRONG>Was the wrapper called with the proper number of
   arguments?</STRONG>
   <BLOCKQUOTE>
    The wrapper will only execute if it is given the proper number of arguments.
    The proper argument format is known to the Apache web server.  If the
    wrapper
    is not receiving the proper number of arguments, it is either being hacked,
    or
    there is something wrong with the suEXEC portion of your Apache binary.
   </BLOCKQUOTE>
  </LI>
  <LI><STRONG>Is the user executing this wrapper a valid user of this
   system?</STRONG>
   <BLOCKQUOTE>
    This is to ensure that the user executing the wrapper is truly a user of the
    system.
   </BLOCKQUOTE>
  </LI>
  <LI><STRONG>Is this valid user allowed to run the wrapper?</STRONG>
   <BLOCKQUOTE>
    Is this user the user allowed to run this wrapper?  Only one user (the
    Apache user) is allowed to execute this program.
   </BLOCKQUOTE>
  </LI>
  <LI><STRONG>Does the target program have an unsafe hierarchical
   reference?</STRONG>
   <BLOCKQUOTE>
    Does the target program contain a leading '/' or have a '..' backreference?
    These are not allowed; the target program must reside within the Apache
    webspace.
   </BLOCKQUOTE>
  </LI>
  <LI><STRONG>Is the target user name valid?</STRONG>
   <BLOCKQUOTE>
    Does the target user exist?
   </BLOCKQUOTE>
  </LI>
  <LI><STRONG>Is the target group name valid?</STRONG>
   <BLOCKQUOTE>
    Does the target group exist?
   </BLOCKQUOTE>
  </LI>
  <LI><STRONG>Is the target user <EM>NOT</EM> superuser?</STRONG>
   <BLOCKQUOTE>
    Presently, suEXEC does not allow 'root' to execute CGI/SSI programs.
   </BLOCKQUOTE>
  </LI>
  <LI><STRONG>Is the target userid <EM>ABOVE</EM> the minimum ID
   number?</STRONG>
   <BLOCKQUOTE>
    The minimum user ID number is specified during configuration.  This allows
    you
    to set the lowest possible userid that will be allowed to execute CGI/SSI
    programs.  This is useful to block out "system" accounts.
   </BLOCKQUOTE>
  </LI>
  <LI><STRONG>Is the target group <EM>NOT</EM> the superuser group?</STRONG>
   <BLOCKQUOTE>
    Presently, suEXEC does not allow the 'root' group to execute CGI/SSI
    programs.
   </BLOCKQUOTE>
  </LI>
  <LI><STRONG>Is the target groupid <EM>ABOVE</EM> the minimum ID
   number?</STRONG>
   <BLOCKQUOTE>
    The minimum group ID number is specified during configuration.  This allows
    you
    to set the lowest possible groupid that will be allowed to execute CGI/SSI
    programs.  This is useful to block out "system" groups.
   </BLOCKQUOTE>
  </LI>
  <LI><STRONG>Can the wrapper successfully become the target user and
   group?</STRONG>
   <BLOCKQUOTE>
    Here is where the program becomes the target user and group via setuid and
    setgid
    calls.  The group access list is also initialized with all of the groups
    of which
    the user is a member.
   </BLOCKQUOTE>
  </LI>
  <LI><STRONG>Does the directory in which the program resides exist?</STRONG>
   <BLOCKQUOTE>
    If it doesn't exist, it can't very well contain files.
   </BLOCKQUOTE>
  </LI>
  <LI><STRONG>Is the directory within the Apache webspace?</STRONG>
   <BLOCKQUOTE>
    If the request is for a regular portion of the server, is the requested
    directory
    within the server's document root?  If the request is for a UserDir, is
    the requested
    directory within the user's document root?
   </BLOCKQUOTE>
  </LI>
  <LI><STRONG>Is the directory <EM>NOT</EM> writable by anyone else?</STRONG>
   <BLOCKQUOTE>
    We don't want to open up the directory to others; only the owner user
    may be able
    to alter this directories contents.
   </BLOCKQUOTE>
  </LI>
  <LI><STRONG>Does the target program exist?</STRONG>
   <BLOCKQUOTE>
    If it doesn't exists, it can't very well be executed.
   </BLOCKQUOTE>
  </LI>
  <LI><STRONG>Is the target program <EM>NOT</EM> writable by anyone
   else?</STRONG>
   <BLOCKQUOTE>
    We don't want to give anyone other than the owner the ability to
    change the program.
   </BLOCKQUOTE>
  </LI>
  <LI><STRONG>Is the target program <EM>NOT</EM> setuid or setgid?</STRONG>
   <BLOCKQUOTE>
    We do not want to execute programs that will then change our UID/GID again.
   </BLOCKQUOTE>
  </LI>
  <LI><STRONG>Is the target user/group the same as the program's
   user/group?</STRONG>
   <BLOCKQUOTE>
    Is the user the owner of the file?
   </BLOCKQUOTE>
  </LI>
  <LI><STRONG>Can we successfully clean the process environment to
   ensure safe operations?</STRONG>
   <BLOCKQUOTE>
    suEXEC cleans the process' environment by establishing a safe
    execution PATH (defined
    during configuration), as well as only passing through those
    variables whose names
    are listed in the safe environment list (also created during
    configuration).
   </BLOCKQUOTE>
  </LI>
  <LI><STRONG>Can we successfully become the target program and
   execute?</STRONG>
   <BLOCKQUOTE>
    Here is where suEXEC ends and the target program begins.
   </BLOCKQUOTE>
  </LI>
 </OL>
 </P>

 <P ALIGN="LEFT">
 This is the standard operation of the the suEXEC wrapper's security model.
 It is somewhat stringent and can impose new limitations and guidelines for
 CGI/SSI design, but it was developed carefully step-by-step with security
 in mind.
 </P>

 <P ALIGN="LEFT">
 For more information as to how this security model can limit your possibilities
 in regards to server configuration, as well as what security risks can be
 avoided with a proper suEXEC setup, see the
 <A HREF="#beware">"Beware the Jabberwock"</A>
 section of this document.
 </P>

 <P ALIGN="CENTER">
 <STRONG><A HREF="suexec.html">BACK TO CONTENTS</A></STRONG>
 </P>

 <H3><A NAME="install">Configuring &amp; Installing suEXEC</A></H3>
 <P ALIGN="LEFT">
 Here's where we begin the fun.  The configuration and installation of suEXEC is
 a four step process: edit the suEXEC header file, compile suEXEC, place the
 suEXEC binary in its proper location, and configure Apache for use with suEXEC.
 </P>

 <P ALIGN="LEFT">
 <STRONG>EDITING THE SUEXEC HEADER FILE</STRONG><BR>
 - From the top-level of the Apache source tree, type:&nbsp;&nbsp;
 <STRONG><CODE>cd support [ENTER]</CODE></STRONG>
 </P>

 <P ALIGN="LEFT">
 Edit the <CODE>suexec.h</CODE> file and change the following macros to
 match your local Apache installation.
 </P>

 <P ALIGN="LEFT">
 <EM>From support/suexec.h</EM>
 <PRE>
      /*
       * HTTPD_USER -- Define as the username under which Apache normally
       *               runs.  This is the only user allowed to execute
       *               this program.
       */
      #define HTTPD_USER "www"

      /*
       * UID_MIN -- Define this as the lowest UID allowed to be a target user
       *            for suEXEC.  For most systems, 500 or 100 is common.
       */
      #define UID_MIN 100

      /*
       * GID_MIN -- Define this as the lowest GID allowed to be a target group
       *            for suEXEC.  For most systems, 100 is common.
       */
      #define GID_MIN 100

      /*
       * USERDIR_SUFFIX -- Define to be the subdirectory under users'
       *                   home directories where suEXEC access should
       *                   be allowed.  All executables under this directory
       *                   will be executable by suEXEC as the user so
       *                   they should be "safe" programs.  If you are
       *                   using a "simple" UserDir directive (ie. one
       *                   without a "*" in it) this should be set to
       *                   the same value.  suEXEC will not work properly
       *                   in cases where the UserDir directive points to
       *                   a location that is not the same as the user's
       *                   home directory as referenced in the passwd file.
       *
       *                   If you have VirtualHosts with a different
       *                   UserDir for each, you will need to define them to
       *                   all reside in one parent directory; then name that
       *                   parent directory here.  IF THIS IS NOT DEFINED
       *                   PROPERLY, ~USERDIR CGI REQUESTS WILL NOT WORK!
       *                   See the suEXEC documentation for more detailed
       *                   information.
       */
      #define USERDIR_SUFFIX "public_html"

      /*
       * LOG_EXEC -- Define this as a filename if you want all suEXEC
       *             transactions and errors logged for auditing and
       *             debugging purposes.
       */
      #define LOG_EXEC "/usr/local/apache/logs/cgi.log" /* Need me? */

      /*
       * DOC_ROOT -- Define as the DocumentRoot set for Apache.  This
       *             will be the only hierarchy (aside from UserDirs)
       *             that can be used for suEXEC behavior.
       */
      #define DOC_ROOT "/usr/local/apache/htdocs"

      /*
       * SAFE_PATH -- Define a safe PATH environment to pass to CGI executables.
       *
       */
      #define SAFE_PATH "/usr/local/bin:/usr/bin:/bin"
 </PRE>
 </P>

 <P ALIGN="LEFT">
 <STRONG>COMPILING THE SUEXEC WRAPPER</STRONG><BR>
 You now need to compile the suEXEC wrapper.  At the shell command prompt,
 after compiling Apache,
 type:&nbsp;&nbsp;<STRONG><CODE>make suexec[ENTER]</CODE></STRONG>.
 This should create the <STRONG><EM>suexec</EM></STRONG> wrapper executable.
 </P>

 <P ALIGN="LEFT">
 <STRONG>COMPILING APACHE FOR USE WITH SUEXEC</STRONG><BR>
 By default, Apache is compiled to look for the suEXEC wrapper in the following
 location.
 </P>

 <P ALIGN="LEFT">
 <EM>From src/httpd.h</EM>
 <PRE>
      /* The path to the suEXEC wrapper */
      #define SUEXEC_BIN "/usr/local/apache/sbin/suexec"
 </PRE>
 </P>

 <P ALIGN="LEFT">
 If your installation requires location of the wrapper program in a different
 directory, edit src/httpd.h and recompile your Apache server.
 See <A HREF="install.html">Compiling and Installing Apache</A> for more
 info on this process.
 </P>

 <P ALIGN="LEFT">
 <STRONG>COPYING THE SUEXEC BINARY TO ITS PROPER LOCATION</STRONG><BR>
 Copy the <STRONG><EM>suexec</EM></STRONG> executable created in the
 exercise above to the defined location for <STRONG>SUEXEC_BIN</STRONG>.
 </P>

 <P ALIGN="LEFT">
 <STRONG><CODE>cp suexec /usr/local/apache/sbin/suexec [ENTER]</CODE></STRONG>
 </P>

 <P ALIGN="LEFT">
 In order for the wrapper to set the user ID, it must me installed as owner
 <STRONG><EM>root</EM></STRONG> and must have the setuserid execution bit
 set for file modes.  If you are not running a <STRONG><EM>root</EM></STRONG>
 user shell, do so now and execute the following commands.
 </P>

 <P ALIGN="LEFT">
 <STRONG><CODE>chown root /usr/local/apache/sbin/suexec [ENTER]</CODE></STRONG>
 <BR>
 <STRONG><CODE>chmod 4711 /usr/local/apache/sbin/suexec [ENTER]</CODE></STRONG>
 </P>

 <P ALIGN="CENTER">
 <STRONG><A HREF="suexec.html">BACK TO CONTENTS</A></STRONG>
 </P>

 <H3><A NAME="enable">Enabling &amp; Disabling suEXEC</A></H3>
 <P ALIGN="LEFT">
 After properly installing the <STRONG>suexec</STRONG> wrapper
 executable, you must kill and restart the Apache server.  A simple
 <STRONG><CODE>kill -1 `cat httpd.pid`</CODE></STRONG> will not be enough.
 Upon startup of the web-server, if Apache finds a properly configured
 <STRONG>suexec</STRONG> wrapper, it will print the following message to
 the console:
 </P>

 <P ALIGN="LEFT">
 <CODE>Configuring Apache for use with suexec wrapper.</CODE>
 </P>

 <P ALIGN="LEFT">
 If you don't see this message at server startup, the server is most
 likely not finding the wrapper program where it expects it, or the
 executable is not installed <STRONG><EM>setuid root</EM></STRONG>. Check
 your installation and try again.
 </P>

 <P ALIGN="LEFT">
 One way to use <STRONG>suEXEC</STRONG> is through the
 <A HREF="mod/core.html#user"><STRONG>User</STRONG></A> and
 <A HREF="mod/core.html#group"><STRONG>Group</STRONG></A> directives in
 <A HREF="mod/core.html#virtualhost"><STRONG>VirtualHost</STRONG></A>
 definitions. By setting these directives to values different from the
 main server user ID, all requests for CGI resources will be executed as
 the <STRONG>User</STRONG> and <STRONG>Group</STRONG> defined for that
 <STRONG>&lt;VirtualHost&gt;</STRONG>. If only one or
 neither of these directives are specified for a
 <STRONG>&lt;VirtualHost&gt;</STRONG> then the main
 server userid is assumed.<P>

 <STRONG>suEXEC</STRONG> can also be used to to execute CGI programs as
 the user to which the request is being directed. This is accomplished by
 using the <STRONG>~</STRONG> character prefixing the user ID for whom
 execution is desired.
 The only requirement needed for this feature to work is for CGI
 execution to be enabled for the user and that the script must meet the
 scrutiny of the <A HREF="#model">security checks</A> above.

 <P ALIGN="CENTER">
 <STRONG><A HREF="suexec.html">BACK TO CONTENTS</A></STRONG>
 </P>

 <H3><A NAME="debug">Debugging suEXEC</A></H3>
 <P ALIGN="LEFT">
 The suEXEC wrapper will write log information to the location defined in
 the <CODE>suexec.h</CODE> as indicated above. If you feel you have
 configured and installed the wrapper properly, have a look at this log
 and the error_log for the server to see where you may have gone astray.
 </P>

 <P ALIGN="CENTER">
 <STRONG><A HREF="suexec.html">BACK TO CONTENTS</A></STRONG>
 </P>

 <H3>
 <A NAME="jabberwock">Beware the Jabberwock: Warnings &amp; Examples</A>
 </H3>
 <P ALIGN="LEFT">
 <STRONG>NOTE!</STRONG>  This section may not be complete.  For the latest
 revision of this section of the documentation, see the Apache Group's
 <A HREF="http://www.apache.org/docs/suexec.html">Online Documentation</A>
 version.
 </P>

 <P ALIGN="LEFT">
 There are a few points of interest regarding the wrapper that can cause
 limitations on server setup.  Please review these before submitting any
 "bugs" regarding suEXEC.
 <UL>
         <LI><STRONG>suEXEC Points Of Interest</STRONG></LI>
         <LI>Hierarchy limitations
         <BLOCKQUOTE>
         For security and efficiency reasons, all suexec requests must
         remain within either a top-level document root for virtual
         host requests, or one top-level personal document root for
         userdir requests.  For example, if you have four VirtualHosts
         configured, you would need to structure all of your VHosts'
         document roots off of one main Apache document hierarchy to
         take advantage of suEXEC for VirtualHosts. (Example forthcoming.)
         </BLOCKQUOTE>
         </LI>
         <LI>suEXEC's PATH environment variable
         <BLOCKQUOTE>
         This can be a dangerous thing to change.  Make certain every
         path you include in this define is a <STRONG>trusted</STRONG>
         directory.  You don't want to open people up to having someone
         from across the world running a trojan horse on them.
         </BLOCKQUOTE>
         </LI>
         <LI>Altering the suEXEC code
         <BLOCKQUOTE>
         Again, this can cause <STRONG>Big Trouble</STRONG> if you try
         this without knowing what you are doing.  Stay away from it
         if at all possible.
         </BLOCKQUOTE>
         </LI>
 </UL>

 <P ALIGN="CENTER">
 <STRONG><A HREF="suexec.html">BACK TO CONTENTS</A></STRONG>
 </P>

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	<H1 ALIGN="CENTER">Apache suEXEC Support</H1>

	<P ALIGN="LEFT">
	<OL>
	<LI><BIG><STRONG>CONTENTS</STRONG></BIG></LI>
	<LI><A HREF="#what">What is suEXEC?</A></LI>
	<LI><A HREF="#before">Before we begin.</A></LI>
	<LI><A HREF="#model">suEXEC Security Model.</A></LI>
	<LI><A HREF="#install">Configuring & Installing suEXEC</A></LI>
	<LI><A HREF="#enable">Enabling & Disabling suEXEC</A></LI>
	<LI><A HREF="#debug">Debugging suEXEC</A></LI>
	<LI><A HREF="#jabberwock">Beware the Jabberwock: Warnings &
	Examples</A></LI>
	</OL>
	</P>

	<H3><A NAME="what">What is suEXEC?</A></H3>
	<P ALIGN="LEFT">
	The <STRONG>suEXEC</STRONG> feature -- introduced in Apache 1.2 -- provides
	Apache users the ability to run <STRONG>CGI</STRONG> and <STRONG>SSI</STRONG>
	programs under user IDs different from the user ID of the calling web-server.
	Normally, when a CGI or SSI program executes, it runs as the same user who is
	running the web server.
	</P>

	<P ALIGN="LEFT">
	Used properly, this feature can reduce considerably the security risks involved
	with allowing users to develop and run private CGI or SSI programs. However,
	if suEXEC is improperly configured, it can cause any number of problems and
	possibly create new holes in your computer's security. If you aren't familiar
	with managing setuid root programs and the security issues they present, we
	highly recommend that you not consider using suEXEC.
	</P>

	<P ALIGN="CENTER">
	<STRONG><A HREF="suexec.html">BACK TO CONTENTS</A></STRONG>
	</P>

	<H3><A NAME="before">Before we begin.</A></H3>
	<P ALIGN="LEFT">
	Before jumping head-first into this document, you should be aware of the
	assumptions made on the part of the Apache Group and this document.
	</P>

	<P ALIGN="LEFT">
	First, it is assumed that you are using a UNIX derivate operating system that
	is capable of <STRONG>setuid</STRONG> and <STRONG>setgid</STRONG> operations.
	All command examples are given in this regard. Other platforms, if they are
	capable of supporting suEXEC, may differ in their configuration.
	</P>

	<P ALIGN="LEFT">
	Second, it is assumed you are familiar with some basic concepts of your
	computer's security and its administration. This involves an understanding
	of <STRONG>setuid/setgid</STRONG> operations and the various effects they
	may have on your system and its level of security.
	</P>

	<P ALIGN="LEFT">
	Third, it is assumed that you are using an <STRONG>unmodified</STRONG>
	version of suEXEC code. All code for suEXEC has been carefully scrutinized and
	tested by the developers as well as numerous beta testers. Every precaution
	has been taken to ensure a simple yet solidly safe base of code. Altering this
	code can cause unexpected problems and new security risks. It is
	<STRONG>highly</STRONG> recommended you not alter the suEXEC code unless you
	are well versed in the particulars of security programming and are willing to
	share your work with the Apache Group for consideration.
	</P>

	<P ALIGN="LEFT">
	Fourth, and last, it has been the decision of the Apache Group to
	<STRONG>NOT</STRONG> make suEXEC part of the default installation of Apache.
	To this end, suEXEC configuration requires of the administrator careful
	attention to details. After due consideration has been given to the various
	settings for suEXEC, the administrator may install suEXEC through normal
	installation methods. The values for these settings need to be carefully
	determined and specified by the administrator to properly maintain system
	security during the use of suEXEC functionality. It is through this detailed
	process that the Apache Group hopes to limit suEXEC installation only to those
	who are careful and determined enough to use it.
	</P>

	<P ALIGN="LEFT">
	Still with us? Yes? Good. Let's move on!
	</P>

	<P ALIGN="CENTER">
	<STRONG><A HREF="suexec.html">BACK TO CONTENTS</A></STRONG>
	</P>

	<H3><A NAME="model">suEXEC Security Model</A></H3>
	<P ALIGN="LEFT">
	Before we begin configuring and installing suEXEC, we will first discuss
	the security model you are about to implement. By doing so, you may
	better understand what exactly is going on inside suEXEC and what precautions
	are taken to ensure your system's security.
	</P>

	<P ALIGN="LEFT">
	<STRONG>suEXEC</STRONG> is based on a setuid "wrapper" program that is
	called by the main Apache web server. This wrapper is called when an HTTP
	request is made for a CGI or SSI program that the administrator has designated
	to run as a userid other than that of the main server. When such a request
	is made, Apache provides the suEXEC wrapper with the program's name and the
	user and group IDs under which the program is to execute.
	</P>

	<P ALIGN="LEFT">
	The wrapper then employs the following process to determine success or
	failure -- if any one of these conditions fail, the program logs the failure
	and exits with an error, otherwise it will continue:
	<OL>
	<LI><STRONG>Was the wrapper called with the proper number of
	arguments?</STRONG>
	<BLOCKQUOTE>
	The wrapper will only execute if it is given the proper number of arguments.
	The proper argument format is known to the Apache web server. If the
	wrapper
	is not receiving the proper number of arguments, it is either being hacked,
	or
	there is something wrong with the suEXEC portion of your Apache binary.
	</BLOCKQUOTE>
	</LI>
	<LI><STRONG>Is the user executing this wrapper a valid user of this
	system?</STRONG>
	<BLOCKQUOTE>
	This is to ensure that the user executing the wrapper is truly a user of the
	system.
	</BLOCKQUOTE>
	</LI>
	<LI><STRONG>Is this valid user allowed to run the wrapper?</STRONG>
	<BLOCKQUOTE>
	Is this user the user allowed to run this wrapper? Only one user (the
	Apache user) is allowed to execute this program.
	</BLOCKQUOTE>
	</LI>
	<LI><STRONG>Does the target program have an unsafe hierarchical
	reference?</STRONG>
	<BLOCKQUOTE>
	Does the target program contain a leading '/' or have a '..' backreference?
	These are not allowed; the target program must reside within the Apache
	webspace.
	</BLOCKQUOTE>
	</LI>
	<LI><STRONG>Is the target user name valid?</STRONG>
	<BLOCKQUOTE>
	Does the target user exist?
	</BLOCKQUOTE>
	</LI>
	<LI><STRONG>Is the target group name valid?</STRONG>
	<BLOCKQUOTE>
	Does the target group exist?
	</BLOCKQUOTE>
	</LI>
	<LI><STRONG>Is the target user <EM>NOT</EM> superuser?</STRONG>
	<BLOCKQUOTE>
	Presently, suEXEC does not allow 'root' to execute CGI/SSI programs.
	</BLOCKQUOTE>
	</LI>
	<LI><STRONG>Is the target userid <EM>ABOVE</EM> the minimum ID
	number?</STRONG>
	<BLOCKQUOTE>
	The minimum user ID number is specified during configuration. This allows
	you
	to set the lowest possible userid that will be allowed to execute CGI/SSI
	programs. This is useful to block out "system" accounts.
	</BLOCKQUOTE>
	</LI>
	<LI><STRONG>Is the target group <EM>NOT</EM> the superuser group?</STRONG>
	<BLOCKQUOTE>
	Presently, suEXEC does not allow the 'root' group to execute CGI/SSI
	programs.
	</BLOCKQUOTE>
	</LI>
	<LI><STRONG>Is the target groupid <EM>ABOVE</EM> the minimum ID
	number?</STRONG>
	<BLOCKQUOTE>
	The minimum group ID number is specified during configuration. This allows
	you
	to set the lowest possible groupid that will be allowed to execute CGI/SSI
	programs. This is useful to block out "system" groups.
	</BLOCKQUOTE>
	</LI>
	<LI><STRONG>Can the wrapper successfully become the target user and
	group?</STRONG>
	<BLOCKQUOTE>
	Here is where the program becomes the target user and group via setuid and
	setgid
	calls. The group access list is also initialized with all of the groups
	of which
	the user is a member.
	</BLOCKQUOTE>
	</LI>
	<LI><STRONG>Does the directory in which the program resides exist?</STRONG>
	<BLOCKQUOTE>
	If it doesn't exist, it can't very well contain files.
	</BLOCKQUOTE>
	</LI>
	<LI><STRONG>Is the directory within the Apache webspace?</STRONG>
	<BLOCKQUOTE>
	If the request is for a regular portion of the server, is the requested
	directory
	within the server's document root? If the request is for a UserDir, is
	the requested
	directory within the user's document root?
	</BLOCKQUOTE>
	</LI>
	<LI><STRONG>Is the directory <EM>NOT</EM> writable by anyone else?</STRONG>
	<BLOCKQUOTE>
	We don't want to open up the directory to others; only the owner user
	may be able
	to alter this directories contents.
	</BLOCKQUOTE>
	</LI>
	<LI><STRONG>Does the target program exist?</STRONG>
	<BLOCKQUOTE>
	If it doesn't exists, it can't very well be executed.
	</BLOCKQUOTE>
	</LI>
	<LI><STRONG>Is the target program <EM>NOT</EM> writable by anyone
	else?</STRONG>
	<BLOCKQUOTE>
	We don't want to give anyone other than the owner the ability to
	change the program.
	</BLOCKQUOTE>
	</LI>
	<LI><STRONG>Is the target program <EM>NOT</EM> setuid or setgid?</STRONG>
	<BLOCKQUOTE>
	We do not want to execute programs that will then change our UID/GID again.
	</BLOCKQUOTE>
	</LI>
	<LI><STRONG>Is the target user/group the same as the program's
	user/group?</STRONG>
	<BLOCKQUOTE>
	Is the user the owner of the file?
	</BLOCKQUOTE>
	</LI>
	<LI><STRONG>Can we successfully clean the process environment to
	ensure safe operations?</STRONG>
	<BLOCKQUOTE>
	suEXEC cleans the process' environment by establishing a safe
	execution PATH (defined
	during configuration), as well as only passing through those
	variables whose names
	are listed in the safe environment list (also created during
	configuration).
	</BLOCKQUOTE>
	</LI>
	<LI><STRONG>Can we successfully become the target program and
	execute?</STRONG>
	<BLOCKQUOTE>
	Here is where suEXEC ends and the target program begins.
	</BLOCKQUOTE>
	</LI>
	</OL>
	</P>

	<P ALIGN="LEFT">
	This is the standard operation of the the suEXEC wrapper's security model.
	It is somewhat stringent and can impose new limitations and guidelines for
	CGI/SSI design, but it was developed carefully step-by-step with security
	in mind.
	</P>

	<P ALIGN="LEFT">
	For more information as to how this security model can limit your possibilities
	in regards to server configuration, as well as what security risks can be
	avoided with a proper suEXEC setup, see the
	<A HREF="#beware">"Beware the Jabberwock"</A>
	section of this document.
	</P>

	<P ALIGN="CENTER">
	<STRONG><A HREF="suexec.html">BACK TO CONTENTS</A></STRONG>
	</P>

	<H3><A NAME="install">Configuring & Installing suEXEC</A></H3>
	<P ALIGN="LEFT">
	Here's where we begin the fun. The configuration and installation of suEXEC is
	a four step process: edit the suEXEC header file, compile suEXEC, place the
	suEXEC binary in its proper location, and configure Apache for use with suEXEC.
	</P>

	<P ALIGN="LEFT">
	<STRONG>EDITING THE SUEXEC HEADER FILE</STRONG><BR>
	- From the top-level of the Apache source tree, type:
	<STRONG><CODE>cd support [ENTER]</CODE></STRONG>
	</P>

	<P ALIGN="LEFT">
	Edit the <CODE>suexec.h</CODE> file and change the following macros to
	match your local Apache installation.
	</P>

	<P ALIGN="LEFT">
	<EM>From support/suexec.h</EM>
	<PRE>
	/*
	* HTTPD_USER -- Define as the username under which Apache normally
	* runs. This is the only user allowed to execute
	* this program.
	*/
	#define HTTPD_USER "www"

	/*
	* UID_MIN -- Define this as the lowest UID allowed to be a target user
	* for suEXEC. For most systems, 500 or 100 is common.
	*/
	#define UID_MIN 100

	/*
	* GID_MIN -- Define this as the lowest GID allowed to be a target group
	* for suEXEC. For most systems, 100 is common.
	*/
	#define GID_MIN 100

	/*
	* USERDIR_SUFFIX -- Define to be the subdirectory under users'
	* home directories where suEXEC access should
	* be allowed. All executables under this directory
	* will be executable by suEXEC as the user so
	* they should be "safe" programs. If you are
	* using a "simple" UserDir directive (ie. one
	* without a "*" in it) this should be set to
	* the same value. suEXEC will not work properly
	* in cases where the UserDir directive points to
	* a location that is not the same as the user's
	* home directory as referenced in the passwd file.
	*
	* If you have VirtualHosts with a different
	* UserDir for each, you will need to define them to
	* all reside in one parent directory; then name that
	* parent directory here. IF THIS IS NOT DEFINED
	* PROPERLY, ~USERDIR CGI REQUESTS WILL NOT WORK!
	* See the suEXEC documentation for more detailed
	* information.
	*/
	#define USERDIR_SUFFIX "public_html"

	/*
	* LOG_EXEC -- Define this as a filename if you want all suEXEC
	* transactions and errors logged for auditing and
	* debugging purposes.
	*/
	#define LOG_EXEC "/usr/local/apache/logs/cgi.log" /* Need me? */

	/*
	* DOC_ROOT -- Define as the DocumentRoot set for Apache. This
	* will be the only hierarchy (aside from UserDirs)
	* that can be used for suEXEC behavior.
	*/
	#define DOC_ROOT "/usr/local/apache/htdocs"

	/*
	* SAFE_PATH -- Define a safe PATH environment to pass to CGI executables.
	*
	*/
	#define SAFE_PATH "/usr/local/bin:/usr/bin:/bin"
	</PRE>
	</P>

	<P ALIGN="LEFT">
	<STRONG>COMPILING THE SUEXEC WRAPPER</STRONG><BR>
	You now need to compile the suEXEC wrapper. At the shell command prompt,
	after compiling Apache,
	type:  <STRONG><CODE>make suexec[ENTER]</CODE></STRONG>.
	This should create the <STRONG><EM>suexec</EM></STRONG> wrapper executable.
	</P>

	<P ALIGN="LEFT">
	<STRONG>COMPILING APACHE FOR USE WITH SUEXEC</STRONG><BR>
	By default, Apache is compiled to look for the suEXEC wrapper in the following
	location.
	</P>

	<P ALIGN="LEFT">
	<EM>From src/httpd.h</EM>
	<PRE>
	/* The path to the suEXEC wrapper */
	#define SUEXEC_BIN "/usr/local/apache/sbin/suexec"
	</PRE>
	</P>

	<P ALIGN="LEFT">
	If your installation requires location of the wrapper program in a different
	directory, edit src/httpd.h and recompile your Apache server.
	See <A HREF="install.html">Compiling and Installing Apache</A> for more
	info on this process.
	</P>

	<P ALIGN="LEFT">
	<STRONG>COPYING THE SUEXEC BINARY TO ITS PROPER LOCATION</STRONG><BR>
	Copy the <STRONG><EM>suexec</EM></STRONG> executable created in the
	exercise above to the defined location for <STRONG>SUEXEC_BIN</STRONG>.
	</P>

	<P ALIGN="LEFT">
	<STRONG><CODE>cp suexec /usr/local/apache/sbin/suexec [ENTER]</CODE></STRONG>
	</P>

	<P ALIGN="LEFT">
	In order for the wrapper to set the user ID, it must me installed as owner
	<STRONG><EM>root</EM></STRONG> and must have the setuserid execution bit
	set for file modes. If you are not running a <STRONG><EM>root</EM></STRONG>
	user shell, do so now and execute the following commands.
	</P>

	<P ALIGN="LEFT">
	<STRONG><CODE>chown root /usr/local/apache/sbin/suexec [ENTER]</CODE></STRONG>
	<BR>
	<STRONG><CODE>chmod 4711 /usr/local/apache/sbin/suexec [ENTER]</CODE></STRONG>
	</P>

	<P ALIGN="CENTER">
	<STRONG><A HREF="suexec.html">BACK TO CONTENTS</A></STRONG>
	</P>

	<H3><A NAME="enable">Enabling & Disabling suEXEC</A></H3>
	<P ALIGN="LEFT">
	After properly installing the <STRONG>suexec</STRONG> wrapper
	executable, you must kill and restart the Apache server. A simple
	<STRONG><CODE>kill -1 `cat httpd.pid`</CODE></STRONG> will not be enough.
	Upon startup of the web-server, if Apache finds a properly configured
	<STRONG>suexec</STRONG> wrapper, it will print the following message to
	the console:
	</P>

	<P ALIGN="LEFT">
	<CODE>Configuring Apache for use with suexec wrapper.</CODE>
	</P>

	<P ALIGN="LEFT">
	If you don't see this message at server startup, the server is most
	likely not finding the wrapper program where it expects it, or the
	executable is not installed <STRONG><EM>setuid root</EM></STRONG>. Check
	your installation and try again.
	</P>

	<P ALIGN="LEFT">
	One way to use <STRONG>suEXEC</STRONG> is through the
	<A HREF="mod/core.html#user"><STRONG>User</STRONG></A> and
	<A HREF="mod/core.html#group"><STRONG>Group</STRONG></A> directives in
	<A HREF="mod/core.html#virtualhost"><STRONG>VirtualHost</STRONG></A>
	definitions. By setting these directives to values different from the
	main server user ID, all requests for CGI resources will be executed as
	the <STRONG>User</STRONG> and <STRONG>Group</STRONG> defined for that
	<STRONG><VirtualHost></STRONG>. If only one or
	neither of these directives are specified for a
	<STRONG><VirtualHost></STRONG> then the main
	server userid is assumed.<P>

	<STRONG>suEXEC</STRONG> can also be used to to execute CGI programs as
	the user to which the request is being directed. This is accomplished by
	using the <STRONG>~</STRONG> character prefixing the user ID for whom
	execution is desired.
	The only requirement needed for this feature to work is for CGI
	execution to be enabled for the user and that the script must meet the
	scrutiny of the <A HREF="#model">security checks</A> above.

	<P ALIGN="CENTER">
	<STRONG><A HREF="suexec.html">BACK TO CONTENTS</A></STRONG>
	</P>

	<H3><A NAME="debug">Debugging suEXEC</A></H3>
	<P ALIGN="LEFT">
	The suEXEC wrapper will write log information to the location defined in
	the <CODE>suexec.h</CODE> as indicated above. If you feel you have
	configured and installed the wrapper properly, have a look at this log
	and the error_log for the server to see where you may have gone astray.
	</P>

	<P ALIGN="CENTER">
	<STRONG><A HREF="suexec.html">BACK TO CONTENTS</A></STRONG>
	</P>

	<H3>
	<A NAME="jabberwock">Beware the Jabberwock: Warnings & Examples</A>
	</H3>
	<P ALIGN="LEFT">
	<STRONG>NOTE!</STRONG> This section may not be complete. For the latest
	revision of this section of the documentation, see the Apache Group's
	<A HREF="http://www.apache.org/docs/suexec.html">Online Documentation</A>
	version.
	</P>

	<P ALIGN="LEFT">
	There are a few points of interest regarding the wrapper that can cause
	limitations on server setup. Please review these before submitting any
	"bugs" regarding suEXEC.
	<UL>
	<LI><STRONG>suEXEC Points Of Interest</STRONG></LI>
	<LI>Hierarchy limitations
	<BLOCKQUOTE>
	For security and efficiency reasons, all suexec requests must
	remain within either a top-level document root for virtual
	host requests, or one top-level personal document root for
	userdir requests. For example, if you have four VirtualHosts
	configured, you would need to structure all of your VHosts'
	document roots off of one main Apache document hierarchy to
	take advantage of suEXEC for VirtualHosts. (Example forthcoming.)
	</BLOCKQUOTE>
	</LI>
	<LI>suEXEC's PATH environment variable
	<BLOCKQUOTE>
	This can be a dangerous thing to change. Make certain every
	path you include in this define is a <STRONG>trusted</STRONG>
	directory. You don't want to open people up to having someone
	from across the world running a trojan horse on them.
	</BLOCKQUOTE>
	</LI>
	<LI>Altering the suEXEC code
	<BLOCKQUOTE>
	Again, this can cause <STRONG>Big Trouble</STRONG> if you try
	this without knowing what you are doing. Stay away from it
	if at all possible.
	</BLOCKQUOTE>
	</LI>
	</UL>

	<P ALIGN="CENTER">
	<STRONG><A HREF="suexec.html">BACK TO CONTENTS</A></STRONG>
	</P>

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