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Cisco Security Advisory: Crafted Packet Causes Reload on Cisco Routers

  • From: Cisco Systems Product Security Incident Response Team
  • Date: Wed Jan 26 11:15:29 2005
  • Prevent-nondelivery-report:

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Hash: SHA1

Cisco Security Advisory: Crafted Packet Causes Reload on Cisco Routers

Revision 1.0

For Public Release 2005 January 26 1600 (GMT)

- --------------------------------------------------------------------------

Contents

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

- --------------------------------------------------------------------------

Summary
=======

Cisco Routers running Internetwork Operating System (IOS) that supports Multi
Protocol Label Switching (MPLS) are vulnerable to a Denial of Service (DoS)
attack on MPLS disabled interfaces. A system that supports MPLS is vulnerable
even if that system is not configured for MPLS.

The vulnerability is only present in Cisco IOS release trains based on 12.1T,
12.2, 12.2T, 12.3 and 12.3T. Releases based on 12.1 mainline, 12.1E and all
releases prior to 12.1 are not vulnerable.

Cisco has made free software available to address this vulnerability.

There are workarounds available to mitigate the effects.

This issue is tracked by CERT/CC VU#583638.

This advisory is available at 
http://www.cisco.com/warp/public/707/cisco-sa-20050126-les.shtml.

Affected Products
=================

Vulnerable Products

Only the following products running a vulnerable version of IOS that support
MPLS are affected.

  * 2600 and 2800 series routers
  * 3600, 3700 and 3800 series routers
  * 4500 and 4700 series routers
  * 5300, 5350 and 5400 series Access Servers

Products that are not listed above are not affected.

MPLS is not supported in IP and IP Plus feature sets. Therefore, products
running an IOS version with an IP or IP Plus feature set are not vulnerable.

An attack can only be launched at systems that are not configured for MPLS
Traffic Engineering and on the interfaces where MPLS is not enabled. MPLS
enabled interfaces can be determined by the show mpls interfaces command.

An unaffacted system where MPLS is not supported will give an output similar to
the following.

    Router#show mpls interfaces
                 ^
      % Invalid input detected at '^' marker.

    Router#


MPLS can be enabled in different ways on a router. In the below output, a
router is shown that has MPLS enabled for IP on interface Ethernet0/0.

      Router#show mpls interfaces
      Interface              IP            Tunnel   Operational
      Ethernet0/0            Yes (tdp)     No       Yes
      Router#


When MPLS for IP is enabled on an interface, the router is immune to the
attacks coming from that interface but vulnerable to the attacks coming from
other interfaces. Enabling MPLS for IP on all interfaces of the router will
make the router immune to attacks coming from any interface. An interface that
has MPLS for IP enabled will have mpls ip or tag-switching ip command in the
interface configuration.

MPLS Traffic Engineering (TE) provides a better protection against this
vulnerability. If MPLS TE is enabled globally, the router will be immune to the
attacks coming from any interface. A router that has MPLS TE enabled will have
mpls traffic-eng tunnels command in the show running-config output.

Products Confirmed Not Vulnerable

  * Products that are not running Cisco IOS are not vulnerable.
  * Products running Cisco IOS versions 12.0 and earlier and 12.1 mainline are
    not vulnerable.
  * Products that are not mentioned in the Affected Products section are not
    vulnerable (including but not limited to Cisco 7200, 7500, 12000 series and
    Catalyst systems).

No other Cisco products are currently known to be affected by these
vulnerabilities.

Details
=======

Multi Protocol Label Switching (MPLS) is a vendor-independent protocol that
integrates layer-2 (as defined in the Open System Interconnection Reference
Model) information into layer-3. More information on MPLS can be found at http:
//www.cisco.com/warp/public/732/Tech/mpls.

A vulnerability exists in the processing of an MPLS packet that is received on
an interface where MPLS is disabled. A router that is configured for MPLS
Traffic Engineering is immune to attacks coming from any interface.

A Cisco device receiving a crafted packet on an MPLS disabled interface will
reset and may take several minutes to become fully functional. This
vulnerability may be exploited repeatedly resulting in an extended DoS attack.
This issue is documented in bugs ID CSCeb56909 ( registered customers only) and
CSCec86420 ( registered customers only) .

Such crafted packets can only be sent from the local network segment.

Impact
======

Successful exploitation of this vulnerability could result in a reload of the
device. Repeated exploitation could result in a sustained DoS attack.

Software Versions and Fixes

+---------------------------------------------+
|  Major Release  | Availability of Repaired  |
|                 |         Releases          |
|-----------------+---------------------------|
| Affected        |          |             |  |
| 12.1-Based      | Rebuild  | Maintenance |  |
| Release         |          |             |  |
|-----------------+------------------------+--|
| 12.1DB          | Migrate to 12.3(4)T or |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.1DC          | Migrate to 12.3(4)T or |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.1T           | Migrate to 12.2 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.1XG          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.1XI          | Migrate to 12.2 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.1XJ          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.1XL          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.1XM          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.1XP          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.1XQ          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.1XR          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.1XT          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.1XU          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.1XV          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.1YA          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.1YB          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.1YC          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.1YD          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.1YE          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.1YF          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.1YH          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.1YI          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| Affected        |          |             |  |
| 12.2-Based      | Rebuild  | Maintenance |  |
| Release         |          |             |  |
|-----------------+----------+-------------+--|
|                 | 12.2     |             |  |
|                 | (10g)    |             |  |
|                 |----------+-------------+--|
|                 | 12.2     |             |  |
|                 | (13e)    |             |  |
|                 |----------+-------------+--|
|                 | 12.2     |             |  |
|                 | (16f)    |             |  |
|                 |----------+-------------+--|
| 12.2            | 12.2     |             |  |
|                 | (17d)    |             |  |
|                 |----------+-------------+--|
|                 | 12.2     |             |  |
|                 | (19b)    |             |  |
|                 |----------+-------------+--|
|                 | 12.2     |             |  |
|                 | (21a)    |             |  |
|                 |----------+-------------+--|
|                 |          | 12.2(23)    |  |
|-----------------+------------------------+--|
|                 | 12.2(2)B through 12.2  |  |
|                 | (4)B7, Migrate to 12.3 |  |
|                 | or later               |  |
|12.2B            |------------------------+--|
|                 | 12.2(4)B8 and forward, |  |
|                 | Migrate to 12.3(4)T or |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2BC          | 12.2(15) |             |  |
|                 | BC2      |             |  |
|-----------------+------------------------+--|
| 12.2BW          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2BX          | Migrate to 12.3(7)XI1  |  |
|                 | or later               |  |
|-----------------+------------------------+--|
| 12.BY           | Migrate to 12.3(4)T or |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2BZ          | Migrate to 12.3(7)XI1  |  |
|                 | or later               |  |
|-----------------+------------------------+--|
| 12.2CX          | Migrate to 12.2(15)BC2 |  |
|-----------------+------------------------+--|
| 12.2CY          | Migrate to 12.2(15)BC2 |  |
|-----------------+------------------------+--|
| 12.2CZ          | 12.2(15)CZ             |  |
|-----------------+------------------------+--|
| 12.2DA          | 12.2(12) |             |  |
|                 | DA6      |             |  |
|-----------------+------------------------+--|
| 12.2DD          | Migrate to 12.3(4)T or |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2DX          | Migrate to 12.3(4)T or |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2EW          |          | 12.2(18)EW  |  |
|-----------------+----------+-------------+--|
| 12.2EWA         |          | 12.2(20)EWA |  |
|-----------------+----------+-------------+--|
| 12.2JA          |          | 12.2(15)JA  |  |
|-----------------+----------+-------------+--|
| 12.2JK          |          | 12.2(15)JK  |  |
|-----------------+------------------------+--|
| 12.2MB          | Migrate to 12.2(19)SW  |  |
|-----------------+------------------------+--|
| 12.2MC          | Migrate to 12.3(11)T   |  |
|-----------------+------------------------+--|
| 12.2MX          | Migrate to 12.3(8)T or |  |
|                 | later                  |  |
|-----------------+------------------------+--|
|                 | 12.2(14) |             |  |
| 12.2S           | S10      |             |  |
|                 |----------+-------------+--|
|                 |          | 12.2(18)S   |  |
|-----------------+----------+-------------+--|
| 12.2SU          |          | 12.2(14)SU  |  |
|-----------------+----------+-------------+--|
| 12.2SW          |          | 12.2(19)SW  |  |
|-----------------+------------------------+--|
| 12.2SX          | Migrate to 12.2(17d)   |  |
|                 | SXB or later           |  |
|-----------------+------------------------+--|
| 12.2SXA         | Migrate to 12.2(17d)   |  |
|                 | SXB or later           |  |
|-----------------+------------------------+--|
| 12.2SXB         |          | 12.2(17d)   |  |
|                 |          | SXB         |  |
|-----------------+----------+-------------+--|
| 12.2SXD         |          | 12.2(18)SXD |  |
|-----------------+------------------------+--|
| 12.2SY          | Migrate to 12.2(17d)   |  |
|                 | SXB or later           |  |
|-----------------+------------------------+--|
| 12.2SZ          | Migrate to 12.2(20)S4  |  |
|-----------------+------------------------+--|
| 12.2T           | 12.2(13) |             |  |
|                 | T14      |             |  |
|-----------------+------------------------+--|
| 12.2XA          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2XB          | 12.2(2)  |             |  |
|                 | XB18     |             |  |
|-----------------+------------------------+--|
| 12.2XC          | Migrate to 12.3T or    |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2XD          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2XE          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2XF          | Migrate to 12.2(15)BC2 |  |
|-----------------+------------------------+--|
| 12.2XG          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2XH          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2XI          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2XJ          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2XK          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2XL          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2XM          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2XN          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2XQ          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2XR          |          | 12.2(15)XR  |  |
|-----------------+------------------------+--|
| 12.2XS          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2XT          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2XU          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2XV          | No plan.               |  |
|-----------------+------------------------+--|
| 12.2XW          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2XZ          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2YA          | 12.2(4)  |             |  |
|                 | YA8      |             |  |
|-----------------+------------------------+--|
| 12.2YB          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2YC          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2YD          | Migrate to 12.3(8)T or |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2YE          | Migrate to 12.2(18)S   |  |
|                 | or later               |  |
|-----------------+------------------------+--|
| 12.2YF          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2YG          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2YH          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2YJ          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2YL          | Migrate to 12.3T or    |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2YM          | Migrate to 12.3T or    |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2YN          | Migrate to 12.3T or    |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2YO          | Migrate to 12.2(17d)   |  |
|                 | SXB or later           |  |
|-----------------+------------------------+--|
| 12.2YQ          | Migrate to 12.3(4)T or |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2YR          | Migrate to 12.3(4)T or |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2YS          | Migrate to 12.3T or    |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2YU          | Migrate to 12.3(2)T or |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2YV          | Migrate to 12.3(4)T or |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2YW          | Migrate to 12.3(2)T or |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2YX          | Migrate to 12.2(14)SU  |  |
|-----------------+------------------------+--|
| 12.2YZ          | Migrate to 12.2(20)S4  |  |
|-----------------+------------------------+--|
| 12.2ZB          | Migrate to 12.3T or    |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2ZC          | Migrate to 12.3T or    |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2ZD          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2ZE          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2ZF          | Migrate to 12.3(4)T or |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2ZG          | Migrate to 12.3(4)T or |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2ZH          | Migrate to 12.3(4)T or |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2ZI          | Migrate to 12.2(18)S   |  |
|                 | or later               |  |
|-----------------+------------------------+--|
| 12.2ZJ          | Migrate to 12.3T or    |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2ZL          | Migrate to 12.3(7)T or |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2ZN          | Migrate to 12.3T or    |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2ZO          | Migrate to 12.3 or     |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.2ZP          | No plan.               |  |
|-----------------+------------------------+--|
| Affected        |          |             |  |
| 12.3-Based      | Rebuild  | Maintenance |  |
| Release         |          |             |  |
|-----------------+----------+-------------+--|
|                 | 12.3(3f) |             |  |
|12.3             |----------+-------------+--|
|                 |          | 12.3(5)     |  |
|-----------------+----------+-------------+--|
| 12.3B           |          | 12.3(5a)B4  |  |
|-----------------+----------+-------------+--|
| 12.3BC          |          | 12.3(9a)BC  |  |
|-----------------+------------------------+--|
| 12.3BW          | Migrate to 12.3(5a)B   |  |
|                 | or later               |  |
|-----------------+------------------------+--|
|                 | 12.3(2)  |             |  |
|                 | T5       |             |  |
|                 |----------+-------------+--|
| 12.3T           | 12.3(4)  |             |  |
|                 | T7       |             |  |
|                 |----------+-------------+--|
|                 |          | 12.3(7)T    |  |
|-----------------+------------------------+--|
| 12.3XA          | Migrate to 12.3(7)T or |  |
|                 | later                  |  |
|-----------------+------------------------+--|
| 12.3XB          | Migrate to 12.3(8)T or |  |
|                 | later                  |  |
|-----------------+------------------------+--|
|                 | Migrate to 12.3(2)XC3  |  |
| 12.3XC          | - Availablility date   |  |
|                 | TBD                    |  |
|-----------------+------------------------+--|
| 12.3XD          | 12.3(4)XD              |  |
|-----------------+------------------------+--|
| 12.3XE          | 12.3(2)XE1             |  |
|-----------------+------------------------+--|
| 12.3XF          | 12.3(2)XF              |  |
|-----------------+------------------------+--|
| 12.3XG          | 12.3(4)  |             |  |
|                 | XG1      |             |  |
|-----------------+------------------------+--|
| 12.3XH          | 12.3(4)XH              |  |
|-----------------+------------------------+--|
| 12.3XI          | 12.3(7)XI              |  |
|-----------------+------------------------+--|
| 12.3XJ          | 12.3(7)XJ              |  |
|-----------------+------------------------+--|
| 12.3XK          | 12.3(4)  |             |  |
|                 | XK1      |             |  |
|-----------------+------------------------+--|
| 12.3XL          | 12.3(7)XL              |  |
|-----------------+------------------------+--|
| 12.3XM          | 12.3(7)XM              |  |
|-----------------+------------------------+--|
| 12.3XN          | 12.3(4)XN              |  |
|-----------------+------------------------+--|
| 12.3XQ          | 12.3(4)XQ              |  |
|-----------------+------------------------+--|
| 12.3XR          | 12.3(7)XR              |  |
|-----------------+------------------------+--|
| 12.3XS          | 12.3(7)XS              |  |
|-----------------+------------------------+--|
| 12.3XT          | 12.3(2)XT              |  |
|-----------------+------------------------+--|
| 12.3XU          | 12.3(8)XU              |  |
|-----------------+------------------------+--|
| 12.3XW          | 12.3(8)XW              |  |
|-----------------+------------------------+--|
| 12.3XX          | 12.3(8)XX              |  |
|-----------------+------------------------+--|
| 12.3XY          | 12.3(8)XY              |  |
|-----------------+------------------------+--|
| 12.3YA          | 12.3(8)YA              |  |
|-----------------+------------------------+--|
| 12.3YD          | 12.3(8)YD              |  |
|-----------------+------------------------+--|
| 12.3YE          | 12.3(4)YE              |  |
|-----------------+------------------------+--|
| 12.3YF          | 12.3(11)YF             |  |
|-----------------+------------------------+--|
| 12.3YG          | 12.3(8)YG              |  |
|-----------------+------------------------+--|
| 12.3YH          | 12.3(8)YH              |  |
+---------------------------------------------+

When considering software upgrades, please also consult http://www.cisco.com/en
/US/products/products_security_advisories_listing.html and any subsequent
advisories to determine exposure and a complete upgrade solution.

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 Technical Assistance Center
(TAC) for assistance.

Obtaining Fixed Software
========================

Customers with Service Contracts

Customers with contracts should obtain upgraded software through their regular
update channels. For most customers, this means that upgrades should be
obtained through the Software Center on Cisco's worldwide website at http://
www.cisco.com.

Customers using Third-party Support Organizations

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
charge.

Customers without Service Contracts

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@cisco.com

Please have your product serial number available and give the URL of this
notice as evidence of your entitlement to a free upgrade. Free upgrades for
non-contract customers must be requested through the TAC.

Please do not contact either "psirt@cisco.com" or "security-alert@cisco.com"
for software upgrades.

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

Customers may only install and expect support for the feature sets they have
purchased. By installing, downloading, accessing or otherwise using such
software upgrades, customers agree to be bound by the terms of Cisco's software
license terms found at http://www.cisco.com/public/sw-license-agreement.html,
or as otherwise set forth at Cisco.com Downloads at http://www.cisco.com/public
/sw-center/sw-usingswc.shtml.

Workarounds
===========

The effectiveness of any workaround is dependent on specific customer
situations such as product mix, network topology, traffic behavior, and
organizational mission. Due to the variety of affected products and releases,
customers should consult with their service provider or support organization to
ensure any applied workaround is the most appropriate for use in the intended
network before it is deployed.

Warning: Using this workaround may affect the operation of your network and
might cause problems. Therefore it is strongly recommended that you do a code
upgrade if you are affected. It is not recommended that you use the workaround
as a long term solution.

Enabling MPLS Traffic Engineering (MPLS TE) globally can be used as a
workaround to mitigate this vulnerability. Since MPLS requires Cisco Express
Forwarding (CEF) in order to work, CEF needs to be enabled first in order to
enable MPLS TE.

CEF and MPLS TE can be enabled by the following commands.

    Router(config)# ip cef
    Router(config)# mpls traffic-eng tunnels


Having MPLS TE enabled will make the router immune to the attacks coming from
any interface.

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 ADVISORY IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF
GUARANTEE OR WARRANTY, INCLUDING THE WARRANTY OF MERCHANTABILITY. YOUR USE OF
THE INFORMATION ON THE ADVISORY OR MATERIALS LINKED FROM THE ADVISORY IS AT
YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS NOTICE AT ANY
TIME.

A stand-alone 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.

Distribution
============

This advisory will be posted on Cisco's worldwide website at 
http://www.cisco.com/warp/public/707/cisco-sa-20050126-les.shtml.

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@cisco.com
  * first-teams@first.org (includes CERT/CC)
  * bugtraq@securityfocus.com
  * vulnwatch@vulnwatch.org
  * cisco@spot.colorado.edu
  * cisco-nsp@puck.nether.net
  * full-disclosure@lists.netsys.com
  * comp.dcom.sys.cisco@newsgate.cisco.com
  * 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 | 2005-January-26 | Initial public |
| 1.0      |                 | 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/en/US/products/products_security_vulnerability_policy.html
. 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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