SMRSH(8)                                                                                                                SMRSH(8)



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 a single directory, by default /etc/smrsh, allowing the system  administrator  to
       choose  the  set  of  acceptable  commands,  and to the shell builtin commands ``exec'', ``exit'', and ``echo''.  It also
       rejects any commands with the characters ``', `<', `>', `;', `$', `(', `)', `\r' (carriage return), or `\n' (newline)  on
       the  command  line  to  prevent  ``end  run''  attacks.   It  allows  ``||'' and ``&&'' to enable commands like: ``"|exec
       /usr/local/bin/filter || exit 75"''

       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 ``/etc/smrsh/vacation''.

       System  administrators should be conservative about populating the /etc/smrsh directory.  For example, a reasonable addi-
       tions is vacation(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 /etc/smrsh 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.   Also,  including  mail
       filtering  programs  such as procmail(1) is a very bad idea.  procmail(1) allows users to run arbitrary programs in their
       procmailrc(5).

FILES
       /etc/smrsh - directory for restricted programs

SEE ALSO
       sendmail(8)



                                                  $Date: 2004/08/06 03:55:35 $                                          SMRSH(8)