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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="#usage">Using 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="#jabberwock">"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. If you use Apache 1.2 or prefer to configure
 Apache 1.3 with the "<CODE>src/Configure</CODE>" script you have to edit
 the suEXEC header file and install the binary in its proper location
 manually. This procedure is described in an
 <A HREF="suexec_1_2.html">extra document</A>.
 The following sections describe the configuration and installation
 for Apache 1.3 with the AutoConf-style interface (APACI).
 </P>

 <P ALIGN="LEFT">
 <STRONG>APACI's suEXEC configuration options</STRONG><BR>
 <DL>
 <DT><CODE>--enable-suexec</CODE>
 <DD>This option enables the suEXEC feature which is never installed or
     activated by default. At least one --suexec-xxxxx option has to be
     provided together with the --enable-suexec option to let APACI
     accept your request for using the suEXEC feature.
 <DT><CODE>--suexec-caller=<EM>UID</EM></CODE>
 <DD>The <A HREF="mod/core.html#user">username</A> under which
     Apache normally runs.
     This is the only user allowed to execute this program.
 <DT><CODE>--suexec-docroot=<EM>DIR</EM></CODE>
 <DD>Define as the DocumentRoot set for Apache.
     This will be the only hierarchy (aside from UserDirs)
     that can be used for suEXEC behavior.
     The default directory is the --datadir value with
     the suffix "/htdocs", <EM>e.g.</EM> if you configure with
     "<CODE>--datadir=/home/apache</CODE>" the directory
     "/home/apache/htdocs" is used as document root for
     the suEXEC wrapper.
 <DT><CODE>--suexec-logfile=<EM>FILE</EM></CODE>
 <DD>This defines the filename to which all suEXEC transactions and
     errors are logged (useful for auditing and debugging purposes).
     By default the logfile is named "suexec_log" and located in your
     standard logfile directory (--logfiledir).
 <DT><CODE>--suexec-userdir=<EM>DIR</EM></CODE>
 <DD>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.
     Default value is "public_html".
     <BR>
     If you have virtual hosts 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.  <STRONG>If this is not defined
     properly, "~userdir" cgi requests will not work!</STRONG>
 <DT><CODE>--suexec-uidmin=<EM>UID</EM></CODE>
 <DD>Define this as the lowest UID allowed to be a target user
     for suEXEC.  For most systems, 500 or 100 is common.
     Default value is 100.
 <DT><CODE>--suexec-gidmin=<EM>GID</EM></CODE>
 <DD>Define this as the lowest GID allowed to be a target group
     for suEXEC. For most systems, 100 is common and therefore
     used as default value.
 <DT><CODE>--suexec-safepath=<EM>PATH</EM></CODE>
 <DD>Define a safe PATH environment to pass to CGI executables.
     Default value is "/usr/local/bin:/usr/bin:/bin".
 </DL>
 </P>

 <P ALIGN="LEFT">
 <STRONG>Checking your suEXEC setup</STRONG><BR>
 Before you compile and install the suEXEC wrapper you can check
 the configuration with the --layout option.
 <BR>
 Example output:
 <PRE>
     suEXEC setup:
             suexec binary: /usr/local/apache/sbin/suexec
             document root: /usr/local/apache/share/htdocs
            userdir suffix: public_html
                   logfile: /usr/local/apache/var/log/suexec_log
                 safe path: /usr/local/bin:/usr/bin:/bin
                 caller ID: www
           minimum user ID: 100
          minimum group ID: 100
 </PRE>
 </P>

 <P ALIGN="LEFT">
 <STRONG>Compiling and installing the suEXEC wrapper</STRONG><BR>
 If you have enabled the suEXEC feature with the --enable-suexec option
 the suexec binary (together with Apache itself) is automatically built
 if you execute the command "make".
 <BR>
 After all components have been built you can execute the command
 "make install" to install them.
 The binary image "suexec" is installed in the directory defined by
 the --sbindir option. Default location is "/usr/local/apache/sbin/suexec".
 <BR>
 Please note that you need <STRONG><EM>root privileges</EM></STRONG> for
 the installation step. In order for the wrapper to set the user ID, it
 must be installed as owner <CODE><EM>root</EM></CODE> and must have the
 setuserid execution bit set for file modes.
 </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">
 Upon startup of Apache, it looks for the file "suexec" in the "sbin"
 directory (default is "/usr/local/apache/sbin/suexec").
 If Apache finds a properly configured suEXEC wrapper, it will print
 the following message to the error log:
 <PRE>
     [notice] suEXEC mechanism enabled (wrapper: <EM>/path/to/suexec</EM>)
 </PRE>
 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 <EM>setuid root</EM>.
 <BR>
 If you want to enable the suEXEC mechanism for the first time
 and an Apache server is already running you must kill and restart Apache.
 Restarting it with a simple HUP or USR1 signal will not be enough.
 <BR>
 If you want to disable suEXEC you should kill and restart Apache after
 you have removed the "suexec" file.
 </P>

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

 <H3><A NAME="usage">Using suEXEC</A></H3>
 <P ALIGN="LEFT">
 <STRONG>Virtual Hosts:</STRONG><BR>
 One way to use the suEXEC wrapper is through the
 <A HREF="mod/core.html#user">User</A> and
 <A HREF="mod/core.html#group">Group</A> directives in
 <A HREF="mod/core.html#virtualhost">VirtualHost</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 <EM>User</EM> and <EM>Group</EM> defined for that
 <CODE>&lt;VirtualHost&gt;</CODE>. If only one or
 neither of these directives are specified for a
 <CODE>&lt;VirtualHost&gt;</CODE> then the main
 server userid is assumed.
 <P>
 <STRONG>User directories:</STRONG><BR>
 The suEXEC wrapper can also be used to execute CGI programs as
 the user to which the request is being directed. This is accomplished by
 using the "<STRONG><CODE>~</CODE></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 file defined
 with the --suexec-logfile option 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="#usage">Using 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="#jabberwock">"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. If you use Apache 1.2 or prefer to configure
	Apache 1.3 with the "<CODE>src/Configure</CODE>" script you have to edit
	the suEXEC header file and install the binary in its proper location
	manually. This procedure is described in an
	<A HREF="suexec_1_2.html">extra document</A>.
	The following sections describe the configuration and installation
	for Apache 1.3 with the AutoConf-style interface (APACI).
	</P>

	<P ALIGN="LEFT">
	<STRONG>APACI's suEXEC configuration options</STRONG><BR>
	<DL>
	<DT><CODE>--enable-suexec</CODE>
	<DD>This option enables the suEXEC feature which is never installed or
	activated by default. At least one --suexec-xxxxx option has to be
	provided together with the --enable-suexec option to let APACI
	accept your request for using the suEXEC feature.
	<DT><CODE>--suexec-caller=<EM>UID</EM></CODE>
	<DD>The <A HREF="mod/core.html#user">username</A> under which
	Apache normally runs.
	This is the only user allowed to execute this program.
	<DT><CODE>--suexec-docroot=<EM>DIR</EM></CODE>
	<DD>Define as the DocumentRoot set for Apache.
	This will be the only hierarchy (aside from UserDirs)
	that can be used for suEXEC behavior.
	The default directory is the --datadir value with
	the suffix "/htdocs", <EM>e.g.</EM> if you configure with
	"<CODE>--datadir=/home/apache</CODE>" the directory
	"/home/apache/htdocs" is used as document root for
	the suEXEC wrapper.
	<DT><CODE>--suexec-logfile=<EM>FILE</EM></CODE>
	<DD>This defines the filename to which all suEXEC transactions and
	errors are logged (useful for auditing and debugging purposes).
	By default the logfile is named "suexec_log" and located in your
	standard logfile directory (--logfiledir).
	<DT><CODE>--suexec-userdir=<EM>DIR</EM></CODE>
	<DD>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.
	Default value is "public_html".
	<BR>
	If you have virtual hosts 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. <STRONG>If this is not defined
	properly, "~userdir" cgi requests will not work!</STRONG>
	<DT><CODE>--suexec-uidmin=<EM>UID</EM></CODE>
	<DD>Define this as the lowest UID allowed to be a target user
	for suEXEC. For most systems, 500 or 100 is common.
	Default value is 100.
	<DT><CODE>--suexec-gidmin=<EM>GID</EM></CODE>
	<DD>Define this as the lowest GID allowed to be a target group
	for suEXEC. For most systems, 100 is common and therefore
	used as default value.
	<DT><CODE>--suexec-safepath=<EM>PATH</EM></CODE>
	<DD>Define a safe PATH environment to pass to CGI executables.
	Default value is "/usr/local/bin:/usr/bin:/bin".
	</DL>
	</P>

	<P ALIGN="LEFT">
	<STRONG>Checking your suEXEC setup</STRONG><BR>
	Before you compile and install the suEXEC wrapper you can check
	the configuration with the --layout option.
	<BR>
	Example output:
	<PRE>
	suEXEC setup:
	suexec binary: /usr/local/apache/sbin/suexec
	document root: /usr/local/apache/share/htdocs
	userdir suffix: public_html
	logfile: /usr/local/apache/var/log/suexec_log
	safe path: /usr/local/bin:/usr/bin:/bin
	caller ID: www
	minimum user ID: 100
	minimum group ID: 100
	</PRE>
	</P>

	<P ALIGN="LEFT">
	<STRONG>Compiling and installing the suEXEC wrapper</STRONG><BR>
	If you have enabled the suEXEC feature with the --enable-suexec option
	the suexec binary (together with Apache itself) is automatically built
	if you execute the command "make".
	<BR>
	After all components have been built you can execute the command
	"make install" to install them.
	The binary image "suexec" is installed in the directory defined by
	the --sbindir option. Default location is "/usr/local/apache/sbin/suexec".
	<BR>
	Please note that you need <STRONG><EM>root privileges</EM></STRONG> for
	the installation step. In order for the wrapper to set the user ID, it
	must be installed as owner <CODE><EM>root</EM></CODE> and must have the
	setuserid execution bit set for file modes.
	</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">
	Upon startup of Apache, it looks for the file "suexec" in the "sbin"
	directory (default is "/usr/local/apache/sbin/suexec").
	If Apache finds a properly configured suEXEC wrapper, it will print
	the following message to the error log:
	<PRE>
	[notice] suEXEC mechanism enabled (wrapper: <EM>/path/to/suexec</EM>)
	</PRE>
	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 <EM>setuid root</EM>.
	<BR>
	If you want to enable the suEXEC mechanism for the first time
	and an Apache server is already running you must kill and restart Apache.
	Restarting it with a simple HUP or USR1 signal will not be enough.
	<BR>
	If you want to disable suEXEC you should kill and restart Apache after
	you have removed the "suexec" file.
	</P>

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

	<H3><A NAME="usage">Using suEXEC</A></H3>
	<P ALIGN="LEFT">
	<STRONG>Virtual Hosts:</STRONG><BR>
	One way to use the suEXEC wrapper is through the
	<A HREF="mod/core.html#user">User</A> and
	<A HREF="mod/core.html#group">Group</A> directives in
	<A HREF="mod/core.html#virtualhost">VirtualHost</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 <EM>User</EM> and <EM>Group</EM> defined for that
	<CODE><VirtualHost></CODE>. If only one or
	neither of these directives are specified for a
	<CODE><VirtualHost></CODE> then the main
	server userid is assumed.
	<P>
	<STRONG>User directories:</STRONG><BR>
	The suEXEC wrapper can also be used to execute CGI programs as
	the user to which the request is being directed. This is accomplished by
	using the "<STRONG><CODE>~</CODE></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 file defined
	with the --suexec-logfile option 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>

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