Login or Register to Ask a Question and Join Our Community

Linux and UNIX Man Pages

Linux & Unix Commands - Search Man Pages

smrsh(8) [debian man page]

SMRSH(8)						      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 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 in order to improve the over all 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/adm/sm.bin, allowing the system administrator to choose the set
       of  acceptable commands, and to the shell builtin commands ``exec'', ``exit'', and ``echo''.  It also rejects any commands with the charac-
       ters ``', `<', `>', `;', `$', `(', `)', `
' (carriage return), or `
' (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/vaca-
       tion'', and ``vacation'' all actually forward to ``/usr/adm/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 direc-
       tory.  Note that this does not restrict the use of shell or perl scripts in the sm.bin directory (using the ``#!'' syntax); it simply  dis-
       allows  execution  of  arbitrary  programs.   Also,  including mail filtering programs such as procmail(1) is a very bad idea.  procmail(1)
       allows users to run arbitrary programs in their procmailrc(5).

COMPILATION

       Compilation should be trivial on most systems.  You may need to use -DSMRSH_PATH="path" to adjust the default search  path  (defaults	to
       ``/bin:/usr/bin:/usr/ucb'') and/or -DSMRSH_CMDDIR="dir" to change the default program directory (defaults to ``/usr/adm/sm.bin'').

FILES

       /usr/adm/sm.bin - default directory for restricted programs on most OSs

       /var/adm/sm.bin - directory for restricted programs on HP UX and Solaris

       /usr/libexec/sm.bin - directory for restricted programs on FreeBSD (>= 3.3) and DragonFly BSD

SEE ALSO

       sendmail(8)

							   $Date: 2004/08/06 03:55:35 $ 						  SMRSH(8)

Check Out this Related Man Page

smrsh(1M)						  System Administration Commands						 smrsh(1M)

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(1M) 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 com-
       mands. It also rejects any commands with the characters: ,, <, >, |, ;, &, $, 
 (<RETURN>), or 
 (<NEWLINE>) on the command line to  pre-
       vent 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

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsr, SUNWcsu		   |
       +-----------------------------+-----------------------------+

SEE ALSO

       sendmail(1M), , attributes(5)

SunOS 5.10							    6 Nov 1998								 smrsh(1M)
Man Page