Cisco Security Advisory: Cisco IOS XR Software Border Gateway Protocol Vulnerability

27 Aug 2010

Cisco IOS XR Software contains a vulnerability in the Border Gateway
Protocol (BGP) feature. The vulnerability manifests itself when a BGP
peer announces a prefix with a specific, valid but unrecognized
transitive attribute. On receipt of this prefix, the Cisco IOS XR
device will corrupt the attribute before sending it to the
neighboring devices. Neighboring devices that receive this corrupted
update may reset the BGP peering session.

Affected devices running Cisco IOS XR Software corrupt the
unrecognized attribute before sending to neighboring devices, but
neighboring devices may be running operating systems other than Cisco
IOS XR Software and may still reset the BGP peering session after
receiving the corrupted update. This is per standards defining the
operation of BGP.

Cisco developed a fix that addresses this vulnerability and will be
releasing free software maintenance upgrades (SMU) progressively
starting 28 August 2010. This advisory will be updated accordingly as
fixes become available.

This advisory is posted at:

http://www.cisco.com/warp/public/707/cisco-sa-20100827-bgp.shtml

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

This vulnerability affects all Cisco IOS XR Software devices
configured with BGP routing.

Vulnerable Products
+------------------

To determine the Cisco IOS XR Software release that is running on a
Cisco product, administrators can log in to the device and issue the 
"show version" command to display the system banner. The system banner
confirms that the device is running Cisco IOS XR Software by
displaying text similar to "Cisco IOS XR Software". The software
version is displayed after the text "Cisco IOS XR Software".

The following example identifies a Cisco CRS-1 that is running Cisco
IOS XR Software Release 3.6.2:

    RP/0/RP0/CPU0:CRS#show version
    Tue Aug 18 14:25:17.407 AEST

    Cisco IOS XR Software, Version 3.6.2[00]
    Copyright (c) 2008 by Cisco Systems, Inc.

    ROM: System Bootstrap, Version 1.49(20080319:195807) [CRS-1 ROMMON],

    CRS uptime is 4 weeks, 4 days, 1 minute
    System image file is "disk0:hfr-os-mbi-3.6.2/mbihfr-rp.vm"

    cisco CRS-8/S (7457) processor with 4194304K bytes of memory.
    7457 processor at 1197Mhz, Revision 1.2

    17 Packet over SONET/SDH network interface(s)
    1 DWDM controller(s)
    17 SONET/SDH Port controller(s)
    8 TenGigabitEthernet/IEEE 802.3 interface(s)
    2 Ethernet/IEEE 802.3 interface(s)
    1019k bytes of non-volatile configuration memory.
    38079M bytes of hard disk.
    981440k bytes of ATA PCMCIA card at disk 0 (Sector size 512 bytes).

    Configuration register on node 0/0/CPU0 is 0x102
    Boot device on node 0/0/CPU0 is mem:

    !--- output truncated

The following example identifies a Cisco 12404 router that is running
Cisco IOS XR Software Release 3.7.1:

    RP/0/0/CPU0:GSR#show version

    Cisco IOS XR Software, Version 3.7.1[00]
    Copyright (c) 2008 by Cisco Systems, Inc.

    ROM: System Bootstrap, Version 12.0(20051020:160303) SOFTWARE
    Copyright (c) 1994-2005 by cisco Systems,  Inc.

    GSR uptime is 3 weeks, 6 days, 3 hours, 20 minutes
    System image file is "disk0:c12k-os-mbi-3.7.1/mbiprp-rp.vm"

    cisco 12404/PRP (7457) processor with 2097152K bytes of memory.
    7457 processor at 1266Mhz, Revision 1.2

    1 Cisco 12000 Series Performance Route Processor
    1 Cisco 12000 Series - Multi-Service Blade Controller
    1 1 Port ISE Packet Over SONET OC-48c/STM-16 Controller (1 POS)
    1 Cisco 12000 Series SPA Interface Processor-601/501/401
    3 Ethernet/IEEE 802.3 interface(s)
    1 SONET/SDH Port controller(s)
    1 Packet over SONET/SDH network interface(s)
    4 PLIM QoS controller(s)
    8 FastEthernet/IEEE 802.3 interface(s)
    1016k bytes of non-volatile configuration memory.
    1000496k bytes of disk0: (Sector size 512 bytes).
    65536k bytes of Flash internal SIMM (Sector size 256k).

    Configuration register on node 0/0/CPU0 is 0x2102
    Boot device on node 0/0/CPU0 is disk0:

    !--- output truncated

Additional information about Cisco IOS XR Software release naming
conventions is available in the "White Paper: Cisco IOS Reference
Guide" at the following link:

http://www.cisco.com/web/about/security/intelligence/ios-ref.html#9

Additional information about Cisco IOS XR Software time-based release
model is available in the "White Paper: Guidelines for Cisco IOS XR
Software" at the following link:

http://www.cisco.com/en/US/prod/collateral/iosswrel/ps8803/ps5845/product_bu...

BGP is configured in Cisco IOS XR Software with the configuration
command "router bgp [AS Number]" or "router bgp [X.Y]". The device is
vulnerable if it is running an affected Cisco IOS XR Software version
and has BGP configured.

The following example shows a Cisco IOS XR Software device configured
with BGP:

    RP/0/0/CPU0:GSR#show running-config | begin router bgp
    Building configuration...
    router bgp 65535
     bgp router-id 192.168.0.1
     address-family ipv4 unicast
      network 192.168.1.1/32
     !
     address-family vpnv4 unicast
     !
     neighbor 192.168.2.1
      remote-as 65534
      update-source Loopback0
      address-family ipv4 unicast
      !

    !--- output truncated

Products Confirmed Not Vulnerable
+--------------------------------

The following Cisco products are confirmed not vulnerable:

  * Cisco IOS Software
  * Cisco IOS XR Software not configured for BGP routing

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

Details
=======

This vulnerability affects Cisco IOS XR devices running affected
software versions and configured with the BGP routing feature.

The vulnerability manifests itself when a BGP peer announces a prefix
with a specific, valid but unrecognized transitive attribute. On
receipt of this prefix, the Cisco IOS XR device will corrupt the
attribute before sending it to the neighboring devices. Neighboring
devices that receive this corrupted update may reset the BGP peering
session.

Affected devices running Cisco IOS XR Software corrupt the
unrecognized attribute before sending to neighboring devices, but
neighboring devices may be running operating systems other than Cisco
IOS XR Software and may still reset the BGP peering session after
receiving the corrupted update. This is per RFC 4271 that defines the
operation of BGP.

After an affected device running Cisco IOS XR Software sends a
corrupted update, it will receive a notification from the neighboring
router and will create a log message like the following example:

    bgp[122]: %ROUTING-BGP-5-ADJCHANGE : neighbor 172.16.1.251 Down - BGP Notification received: update malformed

This vulnerability is documented in Cisco Bug ID CSCti62211 and has
been assigned Common Vulnerabilities and Exposures (CVE) ID
CVE-2010-3035.

Vulnerability Scoring Details
=============================

Cisco has provided scores for the vulnerabilities in this advisory
based on the Common Vulnerability Scoring System (CVSS). The CVSS
scoring in this Security Advisory is done in accordance with CVSS
version 2.0.

CVSS is a standards-based scoring method that conveys vulnerability
severity and helps determine urgency and priority of response.

Cisco has provided a base and temporal score. Customers can then
compute environmental scores to assist in determining the impact of
the vulnerability in individual networks.

Cisco has provided an FAQ to answer additional questions regarding
CVSS at:

http://www.cisco.com/web/about/security/intelligence/cvss-qandas.html

Cisco has also provided a CVSS calculator to help compute the
environmental impact for individual networks at:

http://intellishield.cisco.com/security/alertmanager/cvss

CSCti62211 - BGP flaps due to unknown attribute

CVSS Base Score - 5

Access Vector           - Network
Access Complexity       - Low
Authentication          - None
Confidentiality Impact  - None
Integrity Impact        - None
Availability Impact     - Partial

CVSS Temporal Score - 4.8

Exploitability          - Functional
Remediation Level       - Unavailable
Report Confidence       - Confirmed

Impact
======

Successful exploitation of these vulnerabilities may result in the
continuous resetting of BGP peering sessions. This may lead to
routing inconsistencies and a denial of service for those affected
networks.

Software Versions and Fixes
===========================

When considering software upgrades, also consult:

http://www.cisco.com/go/psirt

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) or your contracted
maintenance provider for assistance.

+-------------------------------------------------------------------+
| Cisco IOS XR  |            SMU ID            |  SMU  |  Requires  |
|    Version    |                              | Name  |   Reload   |
|---------------+------------------------------+-------+------------|
| 3.4.0         | Vulnerable; Migrate to 3.4.3 |       |            |
|               | and apply a SMU              |       |            |
|---------------+------------------------------+-------+------------|
| 3.4.1         | SMU will be available on     |       |            |
|               | 2010-Sep-9                   |       |            |
|---------------+------------------------------+-------+------------|
| 3.4.2         | SMU will be available on     |       |            |
|               | 2010-Sep-9                   |       |            |
|---------------+------------------------------+-------+------------|
| 3.4.3         | SMU will be available on     |       |            |
|               | 2010-Sep-5                   |       |            |
|---------------+------------------------------+-------+------------|
| 3.5.2         | SMU will be available on     |       |            |
|               | 2010-Sep-5                   |       |            |
|---------------+------------------------------+-------+------------|
| 3.5.3         | SMU will be available on     |       |            |
|               | 2010-Sep-9                   |       |            |
|---------------+------------------------------+-------+------------|
| 3.5.4         | SMU will be available on     |       |            |
|               | 2010-Sep-5                   |       |            |
|---------------+------------------------------+-------+------------|
| 3.6.0         | SMU will be available on     |       |            |
|               | 2010-Sep-9                   |       |            |
|---------------+------------------------------+-------+------------|
| 3.6.1         | SMU will be available on     |       |            |
|               | 2010-Sep-3                   |       |            |
|---------------+------------------------------+-------+------------|
| 3.6.2         | SMU will be available on     |       |            |
|               | 2010-Aug-30                  |       |            |
|---------------+------------------------------+-------+------------|
| 3.6.3         | SMU will be available on     |       |            |
|               | 2010-Sep-3                   |       |            |
|---------------+------------------------------+-------+------------|
| 3.7.0         | SMU will be available on     |       |            |
|               | 2010-Sep-9                   |       |            |
|---------------+------------------------------+-------+------------|
| 3.7.1         | SMU will be available on     |       |            |
|               | 2010-Sep-1                   |       |            |
|---------------+------------------------------+-------+------------|
| 3.7.2         | SMU will be available on     |       |            |
|               | 2010-Sep-3                   |       |            |
|---------------+------------------------------+-------+------------|
| 3.7.3         | SMU will be available on     |       |            |
|               | 2010-Sep-3                   |       |            |
|---------------+------------------------------+-------+------------|
| 3.8.0         | SMU will be available on     |       |            |
|               | 2010-Sep-3                   |       |            |
|---------------+------------------------------+-------+------------|
| 3.8.1         | SMU will be available on     |       |            |
|               | 2010-Sep-3                   |       |            |
|---------------+------------------------------+-------+------------|
| 3.8.2         | SMU will be available on     |       |            |
|               | 2010-Aug-30                  |       |            |
|---------------+------------------------------+-------+------------|
| 3.8.3         | SMU will be available on     |       |            |
|               | 2010-Sep-1                   |       |            |
|---------------+------------------------------+-------+------------|
| 3.8.4         | SMU will be available on     |       |            |
|               | 2010-Aug-28                  |       |            |
|---------------+------------------------------+-------+------------|
| 3.9.0         | SMU will be available on     |       |            |
|               | 2010-Sep-1                   |       |            |
|---------------+------------------------------+-------+------------|
| 3.9.1         | SMU will be available on     |       |            |
|               | 2010-Aug-28                  |       |            |
+-------------------------------------------------------------------+

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

There are no workarounds to proactively mitigate this vulnerability.
If a route flap is observed, the prefix with the unrecognized
attribute can be filtered. For further information on filtering on
Cisco IOS XR Software, please consult the document "Implementing
Routing Policy on Cisco IOS XR Software" at the following link:

http://www.cisco.com/en/US/docs/ios_xr_sw/iosxr_r3.0/routing/configuration/g...

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

Cisco is releasing free software updates that address these
vulnerabilities. Prior to deploying software, customers should
consult their maintenance provider or check the software for feature
set compatibility and known issues specific to their environment.

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/en/US/docs/general/warranty/English/EU1KEN_.html

or as otherwise set forth at Cisco.com Downloads at:

http://www.cisco.com/public/sw-center/sw-usingswc.shtml

Do not contact psirt@cisco.com or security-alert@cisco.com for
software upgrades.

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 agreements with third-party support organizations,
such as Cisco Partners, authorized resellers, or service providers
should contact that support organization for guidance and assistance
with the appropriate course of action in regards to this advisory.

The effectiveness of any workaround or fix 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 or
fix is the most appropriate for use in the intended network before it
is deployed.

Customers without Service Contracts
+----------------------------------

Customers who purchase direct from Cisco but do not hold a Cisco
service contract, and customers who purchase through third-party
vendors but are unsuccessful in obtaining fixed software through
their point of sale should acquire 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

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

Refer to:

http://www.cisco.com/en/US/support/tsd_cisco_worldwide_contacts.html

for additional TAC contact information, including localized telephone
numbers, and instructions and e-mail addresses for use in various
languages.

Exploitation and Public Announcements
=====================================

An advertisement of an unrecognized but valid BGP attribute resulted
in resetting of several BGP neighbors on 27 August 2010. This
advertisement was not malicious but inadvertently triggered this
vulnerability.

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

Status of this Notice: INTERIM
==============================

THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY
KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE
INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS
AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS
DOCUMENT AT ANY TIME. CISCO EXPECTS TO UPDATE THIS DOCUMENT AS NEW
INFORMATION BECOMES AVAILABLE.

A stand-alone copy or Paraphrase of the text of this document 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 is posted on Cisco's worldwide website at:

http://www.cisco.com/warp/public/707/cisco-sa-20100827-bgp.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-bulletins@lists.first.org
  * bugtraq@securityfocus.com
  * vulnwatch@vulnwatch.org
  * cisco@spot.colorado.edu
  * cisco-nsp@puck.nether.net
  * full-disclosure@lists.grok.org.uk
  * comp.dcom.sys.cisco@newsgate.cisco.com

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      | 2010-August-27 | 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/en/US/products/products_security_vulnerability_policy.h...

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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Cisco Systems Product Security Incident Response Team

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