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/lib/sendmail.d/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 ``', `<', `>', `;', `$', `(', `)', `
' (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/bin/vacation'', ``/usr/bin/vacation'', ``/home/server/mydir/bin/vaca-
       tion'', and ``vacation'' all actually forward to `/usr/lib/sendmail.d/bin/vacation''.

       System administrators should be conservative about populating the /usr/lib/sendmail.d/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
       /usr/lib/sendmail.d/bin/ directory.  Note that this does not restrict the use of shell or  perl	scripts  in  the  /usr/lib/sendmail.d/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).

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 program directory (defaults to ``/usr/lib/sendmail.d/bin/'').

FILES

       /usr/lib/sendmail.d/bin/ - default directory for restricted programs on SuSE Linux

SEE ALSO

       sendmail(8)

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