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CERT Advisory CA-2003-17 Exploit available for for the Cisco IOS Interface Blocked Vulnerabilities
Original release date: July 18, 2003 Last revised: -- Source: CERT/CC
A complete revision history can be found at the end of this file.
* All Cisco devices running Cisco IOS software and configured to process Internet Protocol version 4 (IPv4) packets
An exploit has been posted publicly for the vulnerability described in VU#411332, which was announced in
An 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 email@example.com 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/
By 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.
Apply a patch from Cisco
Upgrade as described in Cisco's Advisory.
Until 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 http://www.cisco.com/warp/public/707/racl.html http://www.cisco.com/warp/public/707/iacl.html __________
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
Email: firstname.lastname@example.org Phone: +1 412-268-7090 (24-hour hotline) Fax: +1 412-268-6989 Postal address: CERT Coordination Center Software Engineering Institute Carnegie Mellon University Pittsburgh PA 15213-3890 U.S.A. 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.
We strongly urge you to encrypt sensitive information sent by email. Our public PGP key is available from http://www.cert.org/CERT_PGP.key If you prefer to use DES, please call the CERT hotline for more information.
Getting security information
CERT publications and other security information are available from our web site http://www.cert.org/ To subscribe to the CERT mailing list for advisories and bulletins, send email to email@example.com. Please include in the body of your message subscribe cert-advisory * "CERT" and "CERT Coordination Center" are registered in the U.S. Patent and Trademark Office. _______________________________________________________________ NO WARRANTY Any material furnished by Carnegie Mellon University and the Software Engineering Institute is furnished on an "as is" basis. Carnegie Mellon University makes no warranties of any kind, either expressed or implied as to any matter including, but not limited to, warranty of fitness for a particular purpose or merchantability, exclusivity or results obtained from use of the material. Carnegie Mellon University does not make any warranty of any kind with respect to freedom from patent, trademark, or copyright infringement. __________________________________________________________ Conditions for use, disclaimers, and sponsorship information Copyright 2003 Carnegie Mellon University. Revision History
July 18, 2003: Initial release
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