smrsh(1M)

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 programs that he or she can execute.

Briefly, smrsh limits programs to be in the directory /var/adm/sm.bin, allowing the system administrator 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 forward to /var/adm/sm.bin/vacation.

System administrators should be conservative about populating /var/adm/sm.bin. Reasonable additions 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 directory (using the #! syntax); it simply disallows execution of arbitrary programs.

FILES

SEE ALSO

sendmail(1M).