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CA-93:07

Last Revised:  September 19,1997

                Attached copyright statement

        

                                 CERT Advisory

                                April  22,  1993

                   Cisco Router Packet Handling Vulnerability

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The CERT Coordination Center has received information indicating that under

some circumstances Cisco routers will pass IP source routed packets which

should have been denied. Routers which do not use the "no ip source-route"

command are not affected.  This vulnerability applies to all models of Cisco

routers.  This problem occurs with the following releases of software: 8.2,

8.3, 9.0, 9.1 and 9.17.



Cisco Systems and CERT recommend that sites using Cisco routers to provide

firewall protection take action to eliminate this vulnerability from their

networks.



This security issue is fixed in Cisco software releases 8.3(7.2), 9.0(5),

9.1(4) 9.17(2.1) and in all later releases.  Customers who are using software

release 8.2 must upgrade to a later release and should contact Cisco's

Technical Assistance Center (TAC) at 800-553-2447 (Internet: tac@cisco.com)

for more information.



Cisco recommends that customers whose routers may be affected by this

vulnerability upgrade their software to the following versions:



      Release (Update)  

        8.3     (8)

        9.0     (5)

        9.1     (4)

        9.17    (3)



These releases are available on Cisco's Customer Information On-Line (CIO)

service for those customers having a maintenance contract.  Other customers

may obtain these releases through Cisco's Technical Assistance Center or

by contacting their local Cisco distributor.



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I.   Description



     A vulnerability exists in Cisco routers such that a router which 

     is configured to suppress source routed packets with the following

     command:



              no ip source-route



     may allow traffic which should be suppressed.



II.  Impact



     This vulnerability can allow unauthorized traffic to pass through

     the router/gateway.



III. Solution



     Cisco recommends that affected customers upgrade to a later version. 

     Customers who cannot upgrade immediately may be able use access lists 

     to prevent unauthorized traffic. 



     Customers who have questions should contact the Cisco Technical

     Assistance Center at 800-553-2447 for assistance. Internet:

     tac@cisco.com



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The CERT Coordination Center wishes to thank Cisco Systems for responding

to this problem.

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If you believe that your system has been compromised, contact the CERT

Coordination Center or your representative in FIRST (Forum of Incident

Response and Security Teams).



Internet E-mail: cert@cert.org

Telephone: 412-268-7090 (24-hour hotline)

           CERT personnel answer 8:30 a.m.-5:00 p.m. EST(GMT-5)/EDT(GMT-4),

           and are on call for emergencies during other hours.



CERT Coordination Center

Software Engineering Institute

Carnegie Mellon University

Pittsburgh, PA 15213-3890



Past advisories, information about FIRST representatives, and other

information related to computer security are available for anonymous FTP

from cert.org (192.88.209.5).



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Copyright 1993 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 19,1997  Attached Copyright Statement



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