SMRSH(8) SMRSH(8)
11/02/93
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 the directory /usr/adm/sm.bin,
allowing the system administrator to choose the set of acceptable
commands. It also rejects any comma'd(carriageereturn),eor `0', `<',
(newline) on'the&command line to'prevent ``end run'' attacks.
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 populating
/usr/adm/sm.bin. Reasonable additions are vacation(1), procmail(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.
COMPILATION
Compilation should be trivial on most systems. You may need to use
-DPATH=\"path\" to adjust the default search path (defaults to
``/bin:/usr/bin:/usr/ucb'') and/or -DCMDBIN=\"dir\" to change the
default program directory (defaults to ``/usr/adm/sm.bin'').
FILES
/usr/adm/sm.bin - directory for restricted programs
SEE ALSO
sendmail(8)
- 1 - Formatted: October 30, 2025
