smrsh.1m (2010 09)

smrsh(1M) smrsh(1M)

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

conﬁguration ﬁles. It sharply limits the commands that can be run using the

|program syntax of

sendmail in order to improve the overall 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 pro-

grams that he or she can execute.

Brieﬂy,

smrsh limits programs to be in the directory

/var/adm/sm.bin

, allowing the system adminis-

trator to choose the set of acceptable commands. It also rejects any commands with the characters

\, <,

>, |, ;, &

, $, (, ), \r (carriage return), and \n (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 for-

ward to

/var/adm/sm.bin/vacation

System administrators should be conservative about populating

/var/adm/sm.bin. Reasonable addi-

tions are

vacation and rmail. Do not include any shell or shell-like program (such as perl

) in the

sm.bin directory. Note that this does not restrict the use of shell or perl scripts in the

sm.bin direc-

tory (using the

#! syntax); it simply disallows execution of arbitrary programs.

FILES

/var/adm/sm.bin Directory for restricted programs