SMRSH(1M)SMRSH(1M)NAME
smrsh - restricted shell for sendmail
SYNOPSIS
smrsh -c command
DESCRIPTION
The smrsh program is intended as a replacement for the sh command in
the prog mailer in sendmail(1M) configuration files. The smrsh program
sharply limits commands that can be run using the |program syntax of
sendmail. This improves overall system security. smrsh limits the set
of programs that a programmer can execute, even if sendmail runs a pro‐
gram without going through an alias or forward file.
Briefly, smrsh limits programs to be in the directory /var/adm/sm.bin,
allowing system administrators to choose the set of acceptable com‐
mands. It also rejects any commands with the characters: ,, <, >, |, ;,
&, $, \r (RETURN), or \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 forward to/var/adm/sm.bin/vacation.
System administrators should be conservative about populating
/var/adm/sm.bin. Reasonable additions are utilities such as vacation(1)
and procmail. Never include any shell or shell-like program (for exam‐
ple, perl) in the sm.bin directory. This does not restrict the use of
shell or perl scrips in the sm.bin directory (using the #! syntax); it
simply disallows the execution of arbitrary programs.
OPTIONS
The following options are supported:
-c command
Where command is a valid command, executes command.
FILES
/var/adm/sm.bin
directory for restricted programs
SEE ALSOsendmail(1M), , attributes(5)
Nov 6, 1998 SMRSH(1M)