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CA-91:14                        CERT Advisory
                               August 26, 1991
                     SGI "IRIX" /usr/sbin/fmt Vulnerability

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The Computer Emergency Response Team/Coordination Center (CERT/CC) has
received information concerning a vulnerability of mail messages in Silicon
Graphics Computer Systems' IRIX versions prior to 4.0 (this includes all
3.2 and 3.3.* versions).  This problem has been fixed in version 4.0.

Information regarding the exploitation of this vulnerability is inherently 
disclosed by any discussion of the problem (including this Advisory) so 
we recommend taking immediate action. Until you are able to apply the patch, 
mail at your site is vulnerable to being read by any ordinary user logged 
in at that site.

Silicon Graphics has provided the enclosed patch instructions.

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I.   DESCRIPTION:

     A vulnerability exists such that IRIX pre-4.0 (e.g., 3.3.3) systems
     with the basic system software ("eoe1.sw.unix") installed can allow
     unauthorized read access to users' mail messages, by exploiting a
     configuration error in a standard system utility. Due to the ease
     of exploiting this vulnerability and the simplicity of the corrective
     action, the CERT/CC urges all sites to install the patch given below.

II.  IMPACT:

     Anyone who can log in on a given IRIX pre-4.0 (3.2, 3.3, 3.3.*) system
     can read mail messages which have been delivered to any other user on
     that same system.

III. SOLUTION:
        
     As "root", execute the following commands:

	chmod 755 /usr/sbin/fmt
	chown root.sys /usr/sbin/fmt

     If system software should ever be reloaded from a 3.2 or 3.3.*
     installation tape or from a backup tape created before the patch
     was applied, repeat the above procedure immediately after the software
     has been reloaded, before enabling logins by normal users.

     [Fixed in IRIX 4.0.]


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The CERT/CC would like to thank Silicon Graphics for bringing this
vulnerability and solution to our attention.
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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.


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