=============================================================================== Security Advisory CERT-NL =============================================================================== Author/Source : CERT-NL (Erik-Jan Bos) Index : S-93-12 Distribution : World Page : 1 Classification: External Version: Final Subject : Cisco Router Packet Handling Vulnerability Date : 23-Apr-93 =============================================================================== CERT-NL 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-NL 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. ----------------------------------------------------------------------------- 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 --------------------------------------------------------------------------- The CERT Coordination Center wishes to thank Cisco Systems for responding to this problem. --------------------------------------------------------------------------- ============================================================================== CERT-NL is the Computer Emergency Response Team, located in The Netherlands. CERT-NL is a Full Member of the Forum of Incident Response and Security Teams (FIRST). The constituency of CERT-NL are the SURFnet connected institutions. Past CERT-NL Security Bulletins and other CERT-NL related material can be found on the anonymous FTP server of SURFnet bv: "ftp.nic.surfnet.nl" [192.87.46.3], in the directory "netman/cert-nl". This information is also available using email. Send an email saying "help" to "mailserv@nic.surfnet.nl". In case of computer or network security problems please contact CERT-NL or the CERT of your own constituency. Please be aware of the fact that we are are one hour ahead of Universal Time Coordinated (i.e. UTC+0100). Email: cert-nl@surfnet.nl Phone: +31 30 310290 Fax: +31 30 340903 Snailmail: SURFnet bv Attn. CERT-NL P.O. Box 19035 NL - 3501 DA UTRECHT The Netherlands A 7*24h phonenumber is available to SURFnet SSC's and FIRST members on request ============================================================================== --- End of Advisory __ Erik-Jan.