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CA-91:13                        CERT Advisory
	  		       August 23, 1991
                    DEC ULTRIX /usr/bin/mail Vulnerability
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The Computer Emergency Response Team/Coordination Center (CERT/CC) has
received information concerning a vulnerability in all versions of Digital
Equipment Corporation's (DEC) ULTRIX operating system prior to 4.2 and
applicable to all Digital Equipment Corporation architectures.
The vulnerability has been fixed in ULTRIX version 4.2.

This vulnerability allows any user logged into the system to obtain a root
shell. 

Appended is an update to a Digital Equipment Corporation DSNlink/ DSIN FLASH
which describes the vulnerability and Digital Equipment Corporation's
recommended solution.
 
If you have any inquiries regarding Digital Equipment Corporation's document,
please contact your Digital Services Support Organization.

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Start of Digital Equipment Corporation's Document.

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SOURCE: Digital Equipment Corporation.

COPYRIGHT (c) 1988, 1989, 1990 by Digital Equipment Corporation.
ALL RIGHTS RESERVED.
 
 
INFORMATION:
 
ULTRIX V4.1 - Security Vulnerability Identified in /usr/bin/mail
 
 
PROBLEM:
 
A potential security vulnerability has been identified in ULTRIX 
Version  4.1 where, under certain circumstances, user privileges 
can be expanded via /usr/bin/mail.  This problem applies to both  
the VAX and DEC RISC (i.e. DECsystem  and DECstation ) architectures.  
 
As always, Digital urges you to regularly review your system 
management and security procedures.  Digital will continue to review 
and enhance security features, and work with our customers to further
improve the integrity of their systems. 
 
 
SOLUTION:
 
Digital has corrected the identified code as of ULTRIX Version 4.2
(released  May 1991).  Digital recommends strongly that you upgrade to 
ULTRIX Version 4.2 immediately to avoid any potential vulnerability  
to your system via this problem.  For those of you who are unable to 
upgrade at this time, installing the ULTRIX Version 4.2 mail file on 
your V4.1 system will correct this problem.
 
ULTRIX Version 4.2 of /usr/bin/mail has not been shown to be 
compatible with versions of ULTRIX previous to ULTRIX version 4.1; 
upgrading to ULTRIX V4.2 or upgrading to ULTRIX V4.1 and using the 
ULTRIX 4.2 /usr/bin/mail program is required to correct this  
problem.
 
Use one of the procedures below to update an ULTRIX Version 4.1 system:
 
         - Procedure   (1)   describes the process to extract the 
           /usr/bin/mail binary from the ULTRIX Version 4.2 MUP subset. 
 
         - Procedure   (2)   provides the commands to install the 
           ULTRIX Version 4.2 /usr/bin/mail binary from another of your 
           system(s) where possible.
 
         - Both  the  VAX  (DECsystem)  and DEC RISC (DECstation) 
           versions of the ULTRIX Version 4.2 /usr/bin/mail binary, 
	   may be obtained by contacting your Digital Services Support 
           Organization.
 
 
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(1)     This procedure will replace your existing /usr/bin/mail binary using 
        the /usr/bin/mail binary from the ULTRIX Version 4.2 MUP distribution.
        The procedure below describes the method to extract the binary from
        the tape media.
 
NOTE: 
 
Setting the environment to single user mode will prevent possible
disruption of the mail services.
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        To update an ULTRIX Version 4.1 system, you must first obtain the 
        ULTRIX Version 4.2 binary  of  /usr/bin/mail for your computer's  
        architecture from your ULTRIX Version 4.2 distribution tapes.
 
  LOAD THE ULTRIX MANDATORY UPGRADE TAPE ON YOUR ULTRIX Version 4.1 SYSTEM.
 
        ( Note: UDTBASE421 will provide the RISC base upgrade, ULTBASE421 will)
        ( provide the VAX base upgrade mail file.  Substitute as necessary for)
        ( your architecture. )
 
  ( ISSUE THE FOLLOWING COMMANDS FROM YOUR ULTRIX Version 4.1 SYSTEM )

  ( BECOME ROOT - YOU MUST HAVE PRIVILEGES TO MAKE THIS UPDATE. )
  
   % su 
 
  (cd TO SOME DIRECTORY THAT YOU CAN PUT THE FILE IN TEMPORARILY, e.g. cd /tmp)
 
   # cd /tmp 
 
  (NOTE: YOU WILL NEED APPROXIMATELY 2 MB of DISK SPACE )
 
   # mkdir ./usr
   # mkdir ./usr/etc
   # mkdir ./usr/etc/subsets
   # setld -x /dev/nrmt0h {UDTBASE421 or ULTBASE421}
 
 
  ( LIST THE SUBSET, CREATE THE FILE UDTBASE421 or ULTBASE0421, THEN EXTRACT )
  ( THE MAIL FILE /usr/bin/mail {NOTE} THIS EXAMPLE USES THE "RISC" SUBSET   ) 
 
 
   # ls
   # mv UDTBASE421 UDTBASE421.Z
   # zcat UDTBASE421.Z | tar xvf - ./usr/bin/mail
 
  ( MOVE THE ULTRIX V4.2 BINARY TO /usr/bin/mail CHANGE PROTECTION, OWNER etc.)
 
   # cd /usr/bin
   # mv mail mail.old
   # chmod 600 mail.old
   # mv /tmp/usr/bin/mail .
   # chown root mail
   # chgrp kmem mail
   # chmod 6755 mail
        
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(2)    To update the /usr/bin/mail binary from an existing V4.2 
       (similar platform (VAX or RISC)) remote node, copy the 
       file to your system and store it in a temporary location 
       (e.g., - /tmp/mail).
       The procedure below provides an example using DECnet.  Use the 
       copy command that fits your environment to copy the /usr/bin/mail
       binary from a remote node to the /tmp directory on your local
       system.
 
NOTE: 
 
Setting the environment to single user mode will prevent possible
disruption of the mail services.
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 % dcp -iv {remote-nodename}/{username}/{password}::'/usr/bin/mail' '/tmp/mail'
 
  ( ISSUE THE FOLLOWING COMMANDS FROM YOUR ULTRIX Version 4.1 SYSTEM )

  ( BECOME ROOT - YOU MUST HAVE PRIVILEGES TO MAKE THIS UPDATE. )
  
   % su 
   # cd /usr/bin
   # mv mail mail.old
   # chmod 600  mail.old
 
  ( MOVE THE ULTRIX V4.2 BINARY TO /usr/bin/mail CHANGE PROTECTION, OWNER etc.)
                               
   # mv /tmp/mail /usr/bin/mail
   # chown root mail
   # chgrp kmem mail
   # chmod 6755 mail
 
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End of Digital Equipment Corporation Document.
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The CERT/CC would like to thank Tsutomu Shimomura for his assistance and
Digital Equipment Corporation for their response to this vulnerability.
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If you believe that your system has been compromised, contact CERT/CC via
telephone or e-mail.

Computer Emergency Response Team/Coordination Center (CERT/CC)
Software Engineering Institute
Carnegie Mellon University
Pittsburgh, PA 15213-3890

Internet E-mail: cert@cert.org
Telephone: 412-268-7090 24-hour hotline:
           CERT/CC personnel answer 7:30a.m.-6:00p.m. EST,
           on call for emergencies during other hours.

Past advisories and other computer security related information are
available for anonymous ftp from the cert.org (192.88.209.5)
system.

