NAME    [Toc]    [Back]

     smrsh - restricted shell for sendmail

SYNOPSIS    [Toc]    [Back]

     smrsh -c command

DESCRIPTION    [Toc]    [Back]

     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                          ' (carriage  return),  or
     `', `<', `>', `;', `$', `(', `)', `
`0 (newline)
  on  the  command line to prevent ``end run'' attacks.
It allows
     ``||'' and ``&&'' to enable 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 arbitrary
  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    [Toc]    [Back]

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

SEE ALSO    [Toc]    [Back]

     sendmail(8)

OpenBSD      3.6                          October     7,     2003