Re: [Full-Disclosure] Cisco Code Train matrix (mystery IOS vulnerability)

From: Jeremiah Cornelius (
Date: 07/17/03

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    To: <>
    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
    > time.
    Here is CERT:

    CERTŪ 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 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
    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.
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    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
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    * "CERT" and "CERT Coordination Center" are registered in the U.S. Patent
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    Any material furnished by Carnegie Mellon University and the Software
    Engineering Institute is furnished on an "as is" basis. Carnegie Mellon
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    to any matter including, but not limited to, warranty of fitness for a
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    Copyright 2003 Carnegie Mellon University.
    Revision History
    July 16, 2003: Initial release

    Full-Disclosure - We believe in it.

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