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CA-2003-17 Exploit available for for the Cisco IOS Interface Blocked Vulnerabilities


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.

Systems Affected

* 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

I. Description

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 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

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

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

Upgrade as described in Cisco's Advisory.

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:

The CERT Coordination Center thanks Cisco Systems for notifying
us about this problem and for helping us to construct this

Authors: Shawn Hernan and Martin Lindner

This document is available from:

CERT/CC Contact Information

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

Using encryption

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If you prefer to use DES, please call the CERT hotline for more

Getting security information

CERT publications and other security information are available
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* "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 infringement.

Conditions for use, disclaimers, and sponsorship information

Copyright 2003 Carnegie Mellon University.

Revision History

July 18, 2003: Initial release

Version: PGP 6.5.8


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