     SMRSH(8)                                                           SMRSH(8)
                                      11/02/93

     NAME
          smrsh - restricted shell for sendmail

     SYNOPSIS
          smrsh -c command

     DESCRIPTION
          The smrsh program is intended as a replacement for sh for use in the
          ``prog'' mailer in sendmail(8) configuration files.  It sharply limits
          the commands that can be run using the ``|program'' syntax of sendmail
          in order to improve the over all security of your system.  Briefly,
          even if a ``bad guy'' can get sendmail to run a program without going
          through an alias or forward file, smrsh limits the set of programs
          that he or she can execute.

          Briefly, smrsh limits programs to be in the directory /usr/adm/sm.bin,
          allowing the system administrator to choose the set of acceptable
          commands.  It also rejects any comma'd(carriageereturn),eor `0', `<',
          (>newline) on'the&command line to'prevent ``end run'' attacks.

          Initial pathnames on programs are stripped, so forwarding to
          ``/usr/ucb/vacation'', ``/usr/bin/vacation'',
          ``/home/server/mydir/bin/vacation'', and ``vacation'' all actually
          forward to ``/usr/adm/sm.bin/vacation''.

          System administrators should be conservative about populating
          /usr/adm/sm.bin.  Reasonable additions are vacation(1), procmail(1),
          and the like.  No matter how brow-beaten you may be, never include any
          shell or shell-like program (such as perl(1)) in the sm.bin directory.
          Note that this does not restrict the use of shell or perl scripts in
          the sm.bin directory (using the ``#!'' syntax); it simply disallows
          execution of arbitrary programs.

     COMPILATION
          Compilation should be trivial on most systems.  You may need to use
          -DPATH=\"path\" to adjust the default search path (defaults to
          ``/bin:/usr/bin:/usr/ucb'') and/or -DCMDBIN=\"dir\" to change the
          default program directory (defaults to ``/usr/adm/sm.bin'').

     FILES
          /usr/adm/sm.bin - directory for restricted programs

     SEE ALSO
          sendmail(8)

                                        - 1 -        Formatted:  August 25, 2000