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smrsh (8)

SMRSH(8) 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 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 ''/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 ''#!'' syn- tax); 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)