1 .\" Copyright (c) 1998-2004 Sendmail, Inc. and its suppliers.
2 .\" All rights reserved.
3 .\" Copyright (c) 1993 Eric P. Allman. All rights reserved.
5 .\" The Regents of the University of California. All rights reserved.
7 .\" By using this file, you agree to the terms and conditions set
8 .\" forth in the LICENSE file which can be found at the top level of
9 .\" the sendmail distribution.
12 .\" $Id: smrsh.8,v 8.22 2004/08/06 03:55:35 gshapiro Exp $
14 .TH SMRSH 8 "$Date: 2004/08/06 03:55:35 $"
16 smrsh \- restricted shell for sendmail
24 program is intended as a replacement for
26 for use in the ``prog'' mailer in
29 It sharply limits the commands that can be run using the
30 ``|program'' syntax of
32 in order to improve the over all security of your system.
33 Briefly, even if a ``bad guy'' can get sendmail to run a program
34 without going through an alias or forward file,
36 limits the set of programs that he or she can execute.
40 limits programs to be in a single directory,
43 allowing the system administrator to choose the set of acceptable commands,
44 and to the shell builtin commands ``exec'', ``exit'', and ``echo''.
45 It also rejects any commands with the characters
46 `\`', `<', `>', `;', `$', `(', `)', `\er' (carriage return),
48 on the command line to prevent ``end run'' attacks.
49 It allows ``||'' and ``&&'' to enable commands like:
50 ``"|exec /usr/local/bin/filter || exit 75"''
52 Initial pathnames on programs are stripped,
53 so forwarding to ``/usr/ucb/vacation'',
54 ``/usr/bin/vacation'',
55 ``/home/server/mydir/bin/vacation'',
58 all actually forward to
59 ``/usr/adm/sm.bin/vacation''.
61 System administrators should be conservative about populating
63 For example, a reasonable additions is
66 No matter how brow-beaten you may be,
67 never include any shell or shell-like program
73 Note that this does not restrict the use of shell or perl scripts
74 in the sm.bin directory (using the ``#!'' syntax);
75 it simply disallows execution of arbitrary programs.
76 Also, including mail filtering programs such as
80 allows users to run arbitrary programs in their
83 Compilation should be trivial on most systems.
84 You may need to use \-DSMRSH_PATH=\e"\fIpath\fP\e"
85 to adjust the default search path
86 (defaults to ``/bin:/usr/bin:/usr/ucb'')
87 and/or \-DSMRSH_CMDDIR=\e"\fIdir\fP\e"
88 to change the default program directory
89 (defaults to ``/usr/adm/sm.bin'').
91 /usr/adm/sm.bin \- default directory for restricted programs on most OSs
93 /var/adm/sm.bin \- directory for restricted programs on HP UX and Solaris
95 /usr/libexec/sm.bin \- directory for restricted programs on FreeBSD (>= 3.3) and DragonFly BSD