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SMRSH(8)		    System Manager's Manual		      SMRSH(8)

       smrsh - restricted shell	for sendmail

       smrsh -c	command

       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
       /usr/libexec/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  al-
       lows  ``||''  and  ``&&''  to  enable  commands like: ``"|exec /usr/lo-
       cal/bin/filter || exit 75"''

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

       System administrators  should  be  conservative	about  populating  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 ex-
       ecution 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).

       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'') and/or -DSMRSH_CMDDIR=\"dir\"	to change the  default
       program directory (defaults to ``/usr/libexec/sm.bin'').

       /usr/adm/sm.bin - default directory for restricted programs on most OSs

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

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


			 $Date:	2013-11-22 20:52:00 $		      SMRSH(8)


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