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(1M) 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(1), rmail(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 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
/var/adm/sm.bin Directory for restricted programs
SEE ALSO
Hewlett-Packard Company — HP-UX Release 10.20: July 1996