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CERT® Advisory CA-2003-17 Exploit available for the Cisco IOS Interface Blocked VulnerabilitiesOriginal release date: July 18, 2003Last revised: -- Source: CERT/CC A complete revision history can be found at the end of this file. Systems Affected
OverviewAn exploit has been posted publicly for the vulnerability described in VU#411332, which was announced in
I. DescriptionAn exploit has been posted publicly for VU#411332. This exploit allows an attacker to interrupt the normal operation of a vulnerable device. We believe it is likely that intruders will begin using this or other exploits to cause service outages. If you believe you have been the victim of intruder activity related to this vulnerability, we encourage you to report that activity to your local incident response team, if any, and to the CERT Coordination Center. Relevant artifacts or activity can be sent to cert@cert.org with "CERT#24229" in the subject line. If you are not able to communicate via electronic mail, contact CERT/CC by phone at the number listed at the bottom of this document. Many large service providers have already taken action or are in the midst of upgrading. However, if you have not already taken action, we strongly encourage you to review the advisory provided by Cisco and take action in accordance with your site's maintenance and change management procedures. Cisco's advisory can be found at http://www.cisco.com/warp/public/707/cisco-sa-20030717-blocked.shtml The CERT/CC will continue to provide information about this vulnerability through VU#411332. Any information regarding intruder activity related to this vulnerability will be posted to the CERT/CC Currect Activity page, available at http://www.cert.org/current/ II. ImpactBy sending specially crafted IPv4 packets to an interface on a vulnerable device, an intruder can cause the device to stop processing packets destined to that interface. Quoting from Cisco's advisory: A device receiving these specifically crafted IPv4 packets will force the inbound interface to stop processing traffic. The device may stop processing packets destined to the router, including routing protocol packets and ARP packets. No alarms will be triggered, nor will the router reload to correct itself. This issue can affect all Cisco devices running Cisco IOS software. This vulnerability may be exercised repeatedly resulting in loss of availability until a workaround has been applied or the device has been upgraded to a fixed version of code. III. SolutionApply a patch from CiscoUpgrade as described in Cisco's Advisory.Restrict accessUntil a patch can be applied, you can mitigate the risks presented by this vulnerability by judicious use of access control lists (ACLs). The correct use of ACLs depends on your network topology. Additionally, ACLs may degrade performance on some systems. We recommend reviewing the following before applying ACLs: http://www.cisco.com/warp/public/707/cisco-sa-20030717-blocked.shtml#workarounds The CERT Coordination Center thanks Cisco Systems for notifying us about this problem and for helping us to construct this advisory. Authors: Shawn Hernan and Martin Lindner This document is available from: http://www.cert.org/advisories/CA-2003-17.html CERT/CC Contact Information
Phone: +1 412-268-7090 (24-hour hotline) Fax: +1 412-268-6989 Postal address: CERT/CC personnel answer the hotline 08:00-17:00 EST(GMT-5) / EDT(GMT-4) Monday through Friday; they are on call for emergencies during other hours, on U.S. holidays, and on weekends. Using encryptionWe strongly urge you to encrypt sensitive information sent by email. Our public PGP key is available from If you prefer to use DES, please call the CERT hotline for more information. Getting security informationCERT publications and other security information are available from our web site * "CERT" and "CERT Coordination Center" are registered in the U.S. Patent and Trademark Office.
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Copyright 2003 Carnegie Mellon University. Revision History
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