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 lim-
       its the set of programs that he or she can execute.

       Briefly, smrsh limits programs to be in  a  single  direc-
       tory,  by  default  /usr/adm/sm.bin,  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  charac-
       ters  ``',  `<',  `>',  `;', `$', `(', `)', `\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 ``/usr/adm/sm.bin/vacation''.

       System administrators should be conservative  about  popu-
       lating  the  sm.bin  directory.  For example, a reasonable
       additions 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  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.
       Also, including mail  filtering  programs  such  as  proc-
       mail(1)  is  a very bad idea.  procmail(1) allows users to
       run arbitrary programs in their procmailrc(5).

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

FILES
       /usr/adm/sm.bin - default directory  for  restricted  pro-
       grams on most OSs

       /var/adm/sm.bin  - directory for restricted programs on HP
       UX and Solaris

       /usr/libexec/sm.bin - directory for restricted programs on
       FreeBSD (>= 3.3) and DragonFly BSD


SEE ALSO
       sendmail(8)



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