SMRSH(8) Maintenance Commands and Procedures SMRSH(8)

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(8) 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 program 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 commands. 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 example, 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 ALSO

attributes(7), sendmail(8)

June 20, 2021 SMRSH(8)