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Re: Cisco Code Train matrix (mystery IOS vulnerability)
From: "Jeremiah Cornelius" <jeremiah () nur net>
Date: Thu, 17 Jul 2003 00:38:10 -0700

Hi.. merely reporting what information we had available,
and as far as I know it was the ONLY source of information
at the time. Perhaps Cisco could post something sooner next

Here is CERT:


CERT® Advisory CA-2003-15 Cisco IOS Interface Blocked by IPv4 Packet
Original release date: July 16, 2003
Last revised: --
Source: CERT/CC

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

A vulnerability in many versions of Cisco IOS could allow an intruder to
execute a denial-of-service attack against a vulnerable device.

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 We
strongly encourage sites using IOS to read this document and take
appropriate action.
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
Apply a patch 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 of your network topology. Additionally, ACLs may degrade
performace on some systems. We recommend reviewing the following before
applying ACLs

The CERT Coordination Center thanks Cisco Systems of 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

This document is available from:

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

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
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
To subscribe to the CERT mailing list for advisories and bulletins, send
email to majordomo () cert org  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.

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

Conditions for use, disclaimers, and sponsorship information
Copyright 2003 Carnegie Mellon University.
Revision History
July 16, 2003:  Initial release

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