CERT^® Advisory CA-2003-15 Cisco IOS Interface Blocked by IPv4 Packet

A complete revision history can be found at the end of this file.

Systems Affected

• All Cisco devices running Cisco IOS software and configured to process Internet Protocol version 4 (IPv4) packets

Overview

I. Description

Cisco IOS is a very widely deployed network operating system. A vulnerability in IOS could allow an intruder to execute a denial-of-service attack against an affected device. Cisco has published an advisory on this topic, available at

http://www.cisco.com/warp/public/707/cisco-sa-20030717-blocked.shtml

The CERT/CC is tracking this issue as VU#411332. This reference number corresponds to CVE candidate CAN-2003-0567.

II. Impact

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.

III. Solution

Apply a patch from Cisco

Restrict access

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.

Feedback about this advisory may be directed to the author, Shawn Hernan.

CERT/CC Contact Information

Email: cert@cert.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.

Using encryption

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/

* "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

July 16, 2003:  Initial release
July 17, 2003:  Minor formatting changes