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 /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
       ``', `<', `>', `;', `$', `(', `)', `
' (carriage return), or `
' (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/vaca-
       tion'', and ``vacation'' all actually forward to ``/etc/smrsh/vacation''.

       System administrators should be conservative about populating the /etc/smrsh directory.	For  example,  a  reasonable  additions  is  vaca-
       tion(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)