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              The Computer Incident Advisory Capability
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                        Informational Bulletin

            UNIX Security Problem with Silicon Graphics Mail 

October 12, 1990, 0800 PST                                  Number B-2   

CIAC has been learned of a security problem with the Berkeley Mailer
supplied by Silicon Graphics. The program /usr/sbin/Mail on IRIX 3.3
and later releases sets the setgid bit.  This allows users to read any
mail on the system, including mail to root.

To determine if your system has this problem you should execute: 

    ls -l /usr/sbin/Mail  

A line similar to the following should be displayed:

    -rwxr-sr-x   1 bin      mail      172080 Jun  7  15:05 /usr/sbin/Mail

Look at the permission bits.  If you see, "-rwxr-sr-x"  then the
problem exists on your system.

There are several potential solutions for this problem.   

Alternative 1 - Workaround

    Execute the following command as root:

      chmod 755 /usr/sbin/Mail

    Then after doing a ls -l you should see:
  
      -rwxr-xr-x   1 bin      mail      172080 Jun  7  15:05 /usr/sbin/Mail

This workaround has one known side effect.  The Mail program can no
longer remove the user's mail file from /usr/mail when all messages
have been deleted.  Instead, it leaves a zero length file.

If you choose this solution, please be aware that the fixed binary will
be available in the next release of IRIX (3.3.2, currently scheduled
for November, 1990).

Alternative 2 - Obtain and install the fixed binary

A better solution is to download the fixed binary from sgi.com.
Silicon Graphics has made a new executable available to fix this
problem.  It is available for anonymous ftp from sgi.com, or from your
local Silicon Graphics sales representative.  Contact the SGI hotline
for more information. (The bug number is alpha bug AF19315).

If you are not certain how to ftp to sgi.com and properly install the
binary, use the following commands:

  cd /usr/sbin        - The directory that
              Mail is in
  chmod 755 /usr/sbin/Mail    - Remove the setgid bit
  mv /usr/sbin/Mail /usr/sbin/Mail.org  - Rename Mail
  ftp 192.48.153.1       - ftp to sgi.com and
              get the new binary,
  name: anonymous        - login as anonymous
  password: guest          - password guest
  ftp> bin        - Set binary mode
  ftp> cd sgi/Mail      - The Mail directory
  ftp> get Mail        - Get the new binary
  ftp> quit        - quit ftp
  chmod 2755 Mail        - Make sure
              permissions are correct
  chgrp mail Mail        - Make sure group is
              correct 
  chown bin Mail        - Make sure owner is
              correct 

For additional information or assistance, please contact CIAC 

  David Brown
  (415) 423-9878 or (FTS) 543-9878

  FAX:  (415) 423-0913 or (FTS) 543-0913 
 
or send e-mail to:

  ciac@tiger.llnl.gov

The assistance of Kevin E. Leininger and Matt Wicks of Fermi National
Accelerator Laboratory and Chuck Athey and Ross Guant of Lawrence
Livermore National Laboratory is gratefully acknowledged.  Neither the
United States Government nor the University of California nor any of
their employees, makes any warranty,  expressed or implied, or assumes
any legal liability or responsibility for the accuracy, completeness,
or usefulness of any information, product, or process disclosed, or
represents that its use would not infringe privately owned rights.
Reference herein to any specific commercial products, process, or
service by trade name, trademark manufacturer, or otherwise, does not
necessarily constitute or imply its endorsement, recommendation, or
favoring by the United States Government or the University of
California.  The views and opinions of authors expressed herein do not
necessarily state or reflect those of the United States Government nor
the University of California, and shall not be used for advertising or
product endorsement purposes.