MirOS Manual: smrsh(8)

SMRSH(8)                 BSD System Manager's Manual                  SMRSH(8)

NAME

     smrsh - restricted shell for sendmail

SYNOPSIS

     smrsh -c command

DESCRIPTION

     The smrsh program is intended as a replacement for /bin/sh for use in the
     "prog" mailer in sendmail(8) configuration files. It sharply limits the
     commands that can be run using the "|program" syntax of sendmail(8) 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 a single directory, by default
     /usr/libexec/sm.bin, allowing the system administrator to choose the set
     of acceptable commands, and the shell built-in commands "exec", "exit",
     and "echo". It also rejects any commands with the characters '\', '<',
     '>', ';', '$', '(', ')', '\r' (carriage return), or '\n' (newline) on the
     command line to prevent "end run" attacks. It allows "||" and "&&" to en-
     able commands like:

           "|exec /usr/local/bin/filter || exit 75"

     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 /usr/libexec/sm.bin/vacation.

     System administrators should be conservative about populating the sm.bin
     directory. For example, a reasonable additions is vacation(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 arbi-
     trary programs. Also, including mail filtering programs such as procmail
     is a very bad idea. procmail allows users to run arbitrary programs in
     their procmailrc.

FILES

     /usr/libexec/sm.bin  directory for restricted programs

SEE ALSO

     sendmail(8)

MirOS BSD #10-current            June 9, 2014                                1

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