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TUCoPS :: Cisco :: bt660.txt

CERT Advisory CA-2003-15 Cisco IOS Interface Blocked by IPv4 Packet (fwd)

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Muhammad Faisal Rauf Danka

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Subject: CERT Advisory CA-2003-15 Cisco IOS Interface Blocked by IPv4 Packet
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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
   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

   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

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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
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   Conditions for use, disclaimers, and sponsorship information

   Copyright 2003 Carnegie Mellon University.

   Revision History
July 16, 2003:  Initial release

Version: PGP 6.5.8



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