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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

Overview

   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

   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 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:
   http://www.cert.org/advisories/CA-2003-15.html
   ______________________________________________________________________

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

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   http://www.cert.org/

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   Patent and Trademark Office.
   ______________________________________________________________________

   NO WARRANTY
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   Engineering  Institute  is  furnished  on  an  "as is" basis. Carnegie
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     _________________________________________________________________

   Conditions for use, disclaimers, and sponsorship information

   Copyright 2003 Carnegie Mellon University.

   Revision History
July 16, 2003:  Initial release

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