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Advisory ID: cisco-sa-20100827-bgp

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20100827-bgp

Revision 1.7

For Public Release 2010 August 27 22:00  UTC (GMT)

Summary

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 has released free software updates that address this vulnerability.

Cisco IOS devices will not corrupt the unrecognized attribute, however they will reset a BGP session upon receipt of a corrupted or malformed update.

This advisory is posted at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20100827-bgp.

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_bulletin_c25-478699.html.

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 (registered customers only) 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

Calculate the environmental score of CSCti62211

CVSS Base Score - 5

Access Vector

Access Complexity

Authentication

Confidentiality Impact

Integrity Impact

Availability Impact

Network

Low

None

None

None

Partial

CVSS Temporal Score - 4.1

Exploitability

Remediation Level

Report Confidence

Functional

Official-Fix

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 Version

SMU ID

SMU Name

Requires Reload

3.4.0

Vulnerable; Migrate to 3.4.3 and apply a SMU

    

3.4.1

AA04297

AA04303

hfr-rout-3.4.1.CSCti62211

c12k-rout-3.4.1.CSCti62211

No

3.4.2

AA04296

AA04302

hfr-rout-3.4.2.CSCti62211

c12k-rout-3.4.2.CSCti62211

No

3.4.3

AA04295

AA04301

hfr-rout-3.4.3.CSCti62211

c12k-rout-3.4.3.CSCti62211

Yes

3.5.2

AA04292

AA04293

hfr-rout-3.5.2.CSCti62211

c12k-rout-3.5.2.CSCti62211

No

3.5.3

AA04290

AA04291

hfr-rout-3.5.3.CSCti62211

c12k-rout-3.5.3.CSCti62211

No

3.5.4

AA04288

AA04289

hfr-rout-3.5.4.CSCti62211

c12k-rout-3.5.4.CSCti62211

No

3.6.0

AA04285

AA04286

hfr-rout-3.6.0.CSCti62211

c12k-rout-3.6.0.CSCti62211

No

3.6.1

AA04283

AA04284

hfr-rout-3.6.1.CSCti62211

c12k-rout-3.6.1.CSCti62211

Yes

3.6.2

AA04281

AA04282

hfr-rout-3.6.2.CSCti62211

c12k-rout-3.6.2.CSCti62211

No

3.6.3

AA04279

AA04280

hfr-rout-3.6.3.CSCti62211

c12k-rout-3.6.3.CSCti62211

No

3.7.0

AA04299

AA04300

hfr-rout-3.7.0.CSCti62211

c12k-rout-3.7.0.CSCti62211

No

3.7.1

AA04277

AA04278

hfr-rout-3.7.1.CSCti62211

c12k-rout-3.7.1.CSCti62211

No

3.7.2

AA04276

asr9k-rout-3.7.2.CSCti62211

No

3.7.3

AA04275

asr9k-rout-3.7.3.CSCti62211

  

3.8.0

AA04273

AA04274

hfr-rout-3.8.0.CSCti62211

c12k-rout-3.8.0.CSCti62211

No

3.8.1

AA04271

AA04272

hfr-rout-3.8.1.CSCti62211

c12k-rout-3.8.1.CSCti62211

No

3.8.2

AA04269

AA04270

hfr-rout-3.8.2.CSCti62211

c12k-rout-3.8.2.CSCti62211

No

3.8.3

AA04267

AA04268

hfr-rout-3.8.3.CSCti62211

c12k-rout-3.8.3.CSCti62211

No

3.8.4

AA04262

AA04266

hfr-rout-3.8.4.CSCti62211

c12k-rout-3.8.4.CSCti62211

No

3.9.0

AA04267

AA04265

AA04298

hfr-rout-3.9.0.CSCti62211

c12k-rout-3.9.0.CSCti62211

asr9k-rout-3.9.0.CSCti62211

No

3.9.1

AA04261*

AA04263*

AA04287*

hfr-rout-3.9.1.CSCti62211

c12k-rout-3.9.1.CSCti62211

asr9k-rout-3.9.1.CSCti62211

No

* Restart of the BGP process in 3.9.1 may trigger a separate issue and result in RIB-failure if BGP is configured for attribute-download. This issue is specific to 3.9.1 and only surfaces if attribute-download is configured. Please refer to Cisco Bug ID CSCti08859 (registered customers only) for more details and workaround.

Please note that applying the above mentioned SMUs will require a restart of the BGP process. Some of the SMUs will also require a system reboot. This is indicated in the fourth column in the above table.

Installation of the SMU needs to performed in admin mode. An example is shown in the following output:

RP/0/RP1/CPU0:crs#admin
RP/0/RP1/CPU0:crs(admin)#install add ftp://server/hfr-rout-3.9.1.CSCti62211.pie
RP/0/RP1/CPU0:crs(admin)#install activate disk0:hfr-rout-3.9.1.CSCti62211-1.0.0

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/guide/rc3rpl.html#wp1118699.

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: Final

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.

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://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20100827-bgp

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 1.7

2010-September-10

Added reference to CSCti08859.

Revision 1.6

2010-September-06

Updated software table for 3.4.0, 3.4.1, 3.4.2, and 3.4.3. Changed the status to FINAL.

Revision 1.5

2010-September-02

Updated software table for 3.4.3, 3.5.2, 3.5.3, 3.5.4, 3.6.0, 3.6.3, 3.7.0, 3.7.2, 3.7.3 and 3.8.1

Revision 1.4

2010-September-01

Updated software table for 3.5.4, 3.6.1, 3.6.3 and 3.9.0

Revision 1.3

2010-August-31

Updates CVSS score and software table for 3.6.0, 3.6.1, 3.6.2, 3.7.0, 3.8.0 and 3.8.2

Revision 1.2

2010-August-30

Updated software table for 3.7.1, 3.8.0, 3.8.3 and 3.9.0

Revision 1.1

2010-August-29

Updated summary section and software table for 3.9.1 and 3.8.4.

Revision 1.0

2010-August-27

Initial 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.html. This includes instructions for press inquiries regarding Cisco security notices. All Cisco security advisories are available at http://www.cisco.com/go/psirt.