home | help 
SMRSH(8)		     System Manager's Manual			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
     /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 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/bin/va-
     cation'', ``/home/server/mydir/bin/vacation'', and ``vacation''  all  actu-
     ally 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 di-
     rectory (using the ``#!'' syntax); it simply disallows execution  of  arbi-
     trary  programs.	Also,  including  mail	filtering programs such as proc-
     mail(1) is a very bad idea.  procmail(1) allows users to run arbitrary pro-
     grams 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'') and/or -DSMRSH_CMDDIR=\"dir\" to change the default pro-
     gram directory (defaults to ``/usr/libexec/sm.bin'').

FILES
     /usr/adm/sm.bin - default directory for restricted programs 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: 2013-11-22 20:52:00 $			SMRSH(8)
home | help