Cisco Security Advisory: Cisco 6000/6500/7600 Crafted Layer 2 Frame Vulnerability Feb 03 2004 04:40PM
Cisco Systems Product Security Incident Response Team (psirt cisco com)
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Cisco Security Advisory: Cisco 6000/6500/7600 Crafted Layer 2 Frame

Revision 1.0 - FINAL

For Public Release 2004 February 03 1600 UTC (GMT)

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Affected Products
Software Versions and Fixes
Obtaining Fixed Software
Exploitation and Public Announcements
Status of This Notice: FINAL
Revision History
Cisco Security Procedures

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A layer 2 frame (as defined in the Open System Interconnection Reference Model)
that is encapsulating a layer 3 packet (IP, IPX, etc.) may cause Cisco 6000/
6500/7600 series systems with Multilayer Switch Feature Card 2 (MSFC2) that
have a FlexWAN or Optical Services Module (OSM) or that run 12.1(8b)E14 to
freeze or reset, if the actual length of this frame is inconsistent with the
length of the encapsulated layer 3 packet.

This vulnerability may be exploited repeatedly causing a denial of service.

This vulnerability has been addressed by the Cisco Bug IDs CSCdy15598 and

There is no workaround available. A software upgrade is needed to address the

This advisory will be posted on the Cisco worldwide website at

Affected Products

Cisco 6000/6500/7600 series systems with MSFC2 and a FlexWAN or OSM module are

Cisco 6000/6500/7600 series systems with MSFC2 that are running 12.1(8b)E14 are
affected even if they do not have a FlexWAN or OSM module.

Cisco 6000/6500/7600 series systems with a Supervisor 720 are not affected by
this vulnerability.

The affected systems may be running native or hybrid code.

The show module command can be used to determine if there is a FlexWAN or OSM
module on the system. A FlexWAN module will have the part number WS-X6182-2PA.
The OSM modules will have OSM in the part number.

Refer to http://www.cisco.com/warp/public/473/96.html for more information
about determining the type of the the MSFC used on the system.

This vulnerability only affects Cisco 6000/6500/7600 series systems with the
specified hardware or software configuration. All other systems are not
affected by this vulnerability even though they may run affected versions of

To determine the software running on a Cisco product, log in to the device and
issue the show version command to display the system banner. Cisco IOS software
will identify itself as "Internetwork Operating System Software" or simply "IOS
^®". On the next line of output, the image name will be displayed between
parentheses, followed by "Version" and the IOS release name. Other Cisco
devices will not have the show version command or will give different output.

The following example identifies a Cisco product running IOS release 12.1(11b)
E1 with an installed image name of C6MSFC2-JSV-M:

Cisco Internetwork Operating System Software IOS (tm)

MSFC2 Software (C6MSFC2-JSV-M), Version 12.1(11b)E1, EARLY DEPLOYMENT RELEASE


A layer 2 frame that is encapsulating a protocol independent layer 3 packet
(IP, IPX, etc.) may cause Cisco 6000/6500/7600 series systems with an MSFC2 to
freeze or reset. The actual length of the layer 2 frame needs to be
inconsistent with the length of the encapsulated layer 3 packet.

A layer 3 packet that is routed by the Cisco 6000/6500/7600 series systems may
trigger this vulnerability if the packet is encapsulated in a specifically
crafted layer 2 frame. Crafted packets must be software switched on the
vulnerable systems to trigger this vulnerability. The packets that are switched
in hardware will not trigger this vulnerability.

Although such frames can only be sent from the local network segment, there
might be some cases where it is possible to trigger this vulnerability
remotely. For remote exploitation, the crafted layer 2 frames need to pass
through all the intermediate layer 3 devices between the source and the
destination without being clipped. Remote exploitation will not be possible
even if only a single layer 3 device on the path from source to destination
clips the crafted layer 2 frame. To the best of our knowledge, only Cisco 6000/
6500/7600 series will forward such crafted frames without being corrected.

This vulnerability has been addressed by the Cisco Bug IDs CSCdy15598 and

* CSCdy15598 - Affects Cisco 6000/6500/7600 series with an MSFC2 and a
FlexWAN or OSM module. The systems that do not have a FlexWAN or OSM will
not be affected by this bug.

* CSCeb56052 - Affects Cisco 6000/6500/7600 series with an MSFC2 module. Only
12.1(8b)E14 is affected by this bug, other software versions are not
affected. The systems without a FlexWAN or OSM will still be affected by
this bug if they are running 12.1(8b)E14.

You can use the Bug Toolkit ( registered customers only) to look up the details
of these bugs.


The exploitation of this vulnerability can result in freeze or the reset of the
system. A system that is frozen due to this vulnerability can be recovered by a
system reset.

Repeated exploitation may lead to a denial of service until a fixed version of
software has been loaded.

Software Versions and Fixes

Cisco IOS Software

Each row of the table below describes a release train and the platforms or
products for which it is intended. If a given release train is vulnerable, then
the earliest possible releases that contain the fix and the anticipated date of
availability for each are listed in the Rebuild, Interim, and Maintenance
columns. A device running any release in the given train that is earlier than
the release in a specific column (less than the earliest fixed release) is
known to be vulnerable, and it should be upgraded at least to the indicated
release or a later version (greater than the earliest fixed release label).

When selecting a release, keep in mind the following definitions:

* Rebuild-Constructed from the previous maintenance or major release in the
same train, it contains the fix for a specific vulnerability. Although it
receives less testing, it contains only the minimal changes necessary to
effect the repair. Cisco has made available several rebuilds of mainline
trains to address this vulnerability, but strongly recommends running only
the latest maintenance release on mainline trains.

* Interim-Built at regular intervals between maintenance releases and
receives less testing. Interims should be selected only if there is no
other suitable release that addresses the vulnerability, and interim images
should be upgraded to the next available maintenance release as soon as
possible. Interim releases are not available through manufacturing, and
usually they are not available for customer download from CCO without prior
arrangement with the Cisco Technical Assistance Center (TAC).

* Maintenance-Most heavily tested and highly recommended release of any label
in a given row of the table.

In all cases, customers should exercise caution to be certain the devices to be
upgraded contain sufficient memory and that current hardware and software
configurations will continue to be supported properly by the new release. If
the information is not clear, contact the Cisco TAC for assistance, as shown in
the section following this table.

| | Availability of Fixed Releases |
| Trains |------------------------------------|
| | Rebuild | Interim | Maintenance |
| | 12.1(8b) | 12.1 | 12.1(19)E |
| | E15 | (13.5)E | |
| |-----------+----------+-------------|
| 12.1E | 12.1(11b) | - | - |
| | E14 | | |
| |-----------+----------+-------------|
| | 12.1(13) | - | - |
| | E1 | | |
| 12.2SY | - | - | 12.2(14)SY |
| 12.2ZA | - | - | 12.2(14)ZA |

Cisco CatOS Software

Cisco CatOS is not affected by this vulnerability. In the case of hybrid code,
there is no need to change the Cisco CatOS software version.

Obtaining Fixed Software

Customers with contracts should obtain upgraded software free of charge through
their regular update channels. For most customers, this means that upgrades
should be obtained through the Software Center on the Cisco worldwide website
at http://www.cisco.com/tacpage/sw-center/sw-ios.shtml..

Customers whose Cisco products are provided or maintained through prior or
existing agreement with third-party support organizations such as Cisco
Partners, authorized resellers, or service providers should contact that
support organization for assistance with the upgrade, which should be free of

Customers who purchase direct from Cisco but who do not hold a Cisco service
contract and customers who purchase through third-party vendors but are
unsuccessful at obtaining fixed software through their point of sale should get
their upgrades by contacting the Cisco Technical Assistance Center (TAC). TAC
contacts are as follows.

* +1 800 553 2447 (toll free from within North America)

* +1 408 526 7209 (toll call from anywhere in the world)

* e-mail: tac (at) cisco (dot) com [email concealed]

Please have your product serial number available and give the URL of this
notice as evidence of your entitlement to a free upgrade. To ensure prompt
service by email or by phone, please provide your name, company name, address,
product serial number, and current version of Cisco IOS software that you are
using. This can be documented by pasting the output of the show version command
into the text of an email. Free upgrades for non-contract customers must be
requested through the TAC.

Please do not contact either "psirt (at) cisco (dot) com [email concealed]" or "security-alert (at) cisco (dot) com [email concealed]"
for software upgrades.

See http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml for additional
TAC contact information, including special localized telephone numbers,
instructions, and e-mail addresses for use in various languages.


There is no workaround available. The vulnerability can not be mitigated by
reconfiguring the affected systems. A software upgrade is needed.

Exploitation and Public Announcements

The Cisco PSIRT is not aware of any public announcements or malicious use of
the vulnerability described in this advisory.

Status of This Notice: FINAL

This is a final advisory. Although Cisco cannot guarantee the accuracy of all
statements in this advisory, all of the facts have been checked to the best of
our ability. Cisco does not anticipate issuing updated versions of this
advisory unless there is some material change in the facts. Should there be a
significant change in the facts, Cisco will update this advisory.

A standalone copy or paraphrase of the text of this security advisory that
omits the distribution URL in the following section is an uncontrolled copy,
and may lack important information or contain factual errors.


This Advisory will be posted on Cisco's worldwide website at

In addition to worldwide web posting, a text version of this notice is
clear-signed with the Cisco PSIRT PGP key and is posted to the following e-mail
and Usenet news recipients.

* cust-security-announce (at) cisco (dot) com [email concealed]

* bugtraq (at) securityfocus (dot) com [email concealed]

* full-disclosure (at) lists.netsys (dot) com [email concealed]

* first-teams (at) first (dot) org [email concealed] (includes CERT/CC)

* cisco (at) spot.colorado (dot) edu [email concealed]

* cisco-nsp (at) puck.nether (dot) net [email concealed]

* comp.dcom.sys.cisco

* Various internal Cisco mailing lists

Future updates of this advisory, if any, will be placed on Cisco's worldwide
website, but may or may not be actively announced on mailing lists or
newsgroups. Users concerned about this problem are encouraged to check the
above URL for any updates.

Revision History

| Revision | | Initial |
| 1.0 | 2004-February-03 | public |
| | | release. |

Cisco Security Procedures

Complete information on reporting security vulnerabilities in Cisco products,
obtaining assistance with security incidents, and registering to receive
security information from Cisco, is available on Cisco's worldwide website at
http://www.cisco.com/warp/public/707/sec_incident_response.shtml. This includes
instructions for press inquiries regarding Cisco security notices. All Cisco
security advisories are available at http://www.cisco.com/go/psirt.

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All contents are Copyright © 1992-2004 Cisco Systems, Inc. All rights reserved.
Important Notices and Privacy Statement.
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Updated: Feb 03, 2004 Document ID: 47980

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