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CA-91:17    

Last Revised: September 18,1997

                Attached copyright statement

                

                              CERT Advisory

                              September 26, 1991

                      DECnet-Internet Gateway Vulnerability



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The Computer Emergency Response Team/Coordination Center (CERT/CC) has

received information concerning a vulnerability in the configuration of

the DECnet-Internet gateway software for Digital Equipment Corporation's 

(DEC) ULTRIX versions 4.0, 4.1, and 4.2 on all Digital architectures.



Digital Equipment Corporation is aware of this problem and a resolution

for this vulnerability will be included in a future release.  Digital

and the CERT/CC strongly recommend that sites exposed to this vulnerability 

immediately institute the workaround detailed in this advisory.



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I.   Description



     When installing the DECnet-Internet gateway software it is necessary to

     create a guest account on the ULTRIX gateway host.  By default, this

     account has /bin/csh as its shell.  By virtue of the guest account

     having a valid shell, the DECnet-Internet gateway software can be

     exploited to allow unauthorized root access.



II.  Impact



     Anyone using the DECnet-Internet gateway can gain unauthorized

     root privileges on the ULTRIX gateway host.



III. Solution

        

     This section describes a workaround for this vulnerability.



     Disable the guest account by editing the /etc/passwd file and setting

     the shell field for the guest account to /bin/false.  Also, ensure the 

     guest account has the string "NoLogin" in the password field as detailed

     in the DECnet-Internet installation manual.  



     Even if you have not installed or are not running the DECnet-

     Internet gateway software, Digital recommends that you implement the

     workaround solution stated above.



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The CERT/CC wishes to thank R. Scott Butler of the Du Pont Company for 

bringing this vulnerability to our attention and for his further 

assistance with the temporary workaround.

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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/EDT,

           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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Copyright 1991 Carnegie Mellon University. Conditions for use, disclaimers,

and sponsorship information can be found in

http://www.cert.org/legal_stuff.html and http://ftp.cert.org/pub/legal_stuff .

If you do not have FTP or web access, send mail to cert@cert.org with

"copyright" in the subject line.



CERT is registered in the U.S. Patent and Trademark Office.



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Revision History



September 18,1997  Attached Copyright Statement



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