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CA-93:07                         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).

