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SMRSH(8) SMRSH(8)
[1mNAME[0m
smrsh - restricted shell for sendmail
[1mSYNOPSIS[0m
[1msmrsh -c [22mcommand
[1mDESCRIPTION[0m
The [4msmrsh[24m program is intended as a replacement for [4msh[24m for use in the
``prog'' mailer in [4msendmail[24m(8) configuration files. It sharply limits
the commands that can be run using the ``|program'' syntax of [4msendmail[0m
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, [4msmrsh[24m limits the set of programs that
he or she can execute.
Briefly, [4msmrsh[24m limits programs to be in a single directory, by default
/usr/adm/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
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/vacation'', and ``vacation'' all actually for-
ward to ``/usr/adm/sm.bin/vacation''.
System administrators should be conservative about populating the
sm.bin directory. For example, a reasonable additions is [4mvacation[24m(1),
and the like. No matter how brow-beaten you may be, never include any
shell or shell-like program (such as [4mperl[24m(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. Also, including mail filtering pro-
grams such as [4mprocmail[24m(1) is a very bad idea. [4mprocmail[24m(1) allows users
to run arbitrary programs in their [4mprocmailrc[24m(5).
[1mCOMPILATION[0m
Compilation should be trivial on most systems. You may need to use
-DSMRSH_PATH=\"[4mpath[24m\" to adjust the default search path (defaults to
``/bin:/usr/bin:/usr/ucb'') and/or -DSMRSH_CMDDIR=\"[4mdir[24m\" to change the
default program directory (defaults to ``/usr/adm/sm.bin'').
[1mFILES[0m
/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
[1mSEE ALSO[0m
sendmail(8)
$Date: 2013-11-22 20:52:00 $ SMRSH(8)
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