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


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From: Cisco Systems Product Security Incident Response Team <psirt@cisco.com.>
To: bugtraq@securityfocus.com
Subject: Cisco Security Advisory: Cisco Security Advisory: Cisco IOS XR Software Border Gateway Protocol Vulnerability
Date: Tue, 18 Jul 2009 16:25:00 -0000
Message-id: <20090818.bgp@psirt.cisco.com.>
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Cisco Security Advisory: Cisco Security Advisory: Cisco IOS XR
Software Border Gateway Protocol Vulnerability

Advisory ID: cisco-sa-20090818-bgp

http://www.cisco.com/warp/public/707/cisco-sa-20090818-bgp.shtml

Revision 1.0

For Public Release 2009 August 18 1500 UTC (GMT)

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


Summary
=======

Cisco IOS XR will reset a Border Gateway Protocol (BGP) peering
session when receiving a specific invalid BGP update.

The vulnerability manifests when a BGP peer announces a prefix with a
specific invalid attribute. On receipt of this prefix, the Cisco IOS
XR device will restart the peering session by sending a notification.
The peering session will flap until the sender stops sending the
invalid/corrupt update.

This is a different vulnerability to what was disclosed in the Cisco
Security Advisory "Cisco IOS Software Border Gateway Protocol 4-Byte
Autonomous System Number Vulnerabilities" disclosed on the 2009 July
29 1600 UTC at the following link: 

http://www.cisco.com/warp/public/707/cisco-sa-20090729-bgp.shtml

Cisco is preparing to release free software maintenance upgrade (SMU)
that address this vulnerability. This advisory will be updated once
the SMU is available.

A workaround that mitigates this vulnerability is available.

This advisory is posted at 

http://www.cisco.com/warp/public/707/cisco-sa-20090818-bgp.shtml

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

This vulnerability affects all Cisco IOS XR software devices after
and including software release 3.4.0 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/warp/public/620/1.html#t6

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 affected Cisco IOS XR 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 prior to release 3.4.0
  * Cisco IOS XR Software not configured for BGP routing


No other Cisco products are currently known to be affected by this
vulnerability.

Details
=======

On August 17th, 2009, a widely-distributed Border Gateway Protocol
(BGP) route update contained an BGP Update message with a specific
invalid attribute. When the invalid BGP Update message was processed
by Cisco IOS XR software, it began resetting BGP peering sessions
over which the update was received.

When receiving the invalid update the receiving Cisco IOS XR software
device will display a log message like the following example:

    RP/0/RP0/CPU0:Aug 17 13:47:05.896 GMT: bgp[122]: %ROUTING-BGP-5-ADJCHANGE : neighbor 192.168.0.1 Down - BGP Notification sent: invalid or corrupt AS path 
    

The peering session will flap until the sender stops sending the
invalid/corrupt prefix.

This vulnerability is documented in Cisco Bug ID CSCtb42995 ( 
registered customers only) and has been assigned Common
Vulnerabilities and Exposures (CVE) ID CVE-2009-2055.

Vulnerability Scoring Details

Cisco has provided scores for the vulnerability 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 CSCtb42995 - Cisco IOS XR Software Border Gateway Protocol Vulnerability +----------------------------------------------------- CVSS Base Score - 4.3 Access Vector - Network Access Complexity - Medium Authentication - None Confidentiality Impact - None Integrity Impact - None Availability Impact - Partial CVSS Temporal Score - 3.9 Exploitability - Functional Remediation Level - Unavailable Report Confidence - Confirmed Impact ====== Successful exploitation of the vulnerability may result in BGP peering sessions continuously being reset. 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 | |----------------------+----------------| | 3.2.X | Not Vulnerable | |----------------------+----------------| | 3.3.X | Not vulnerable | |----------------------+----------------| | 3.4.0 | Pending | |----------------------+----------------| | 3.4.1 | Pending | |----------------------+----------------| | 3.4.2 | Pending | |----------------------+----------------| | 3.4.3 | Pending | |----------------------+----------------| | 3.5.2 | Pending | |----------------------+----------------| | 3.5.3 | Pending | |----------------------+----------------| | 3.5.4 | Pending | |----------------------+----------------| | 3.6.0 | Pending | |----------------------+----------------| | 3.6.1 | Pending | |----------------------+----------------| | 3.6.2 | Pending | |----------------------+----------------| | 3.6.3 | Pending | |----------------------+----------------| | 3.7.0 | Pending | |----------------------+----------------| | 3.7.1 | Pending | |----------------------+----------------| | 3.7.2 | Pending | |----------------------+----------------| | 3.7.3 | Pending | |----------------------+----------------| | 3.8.0 | Pending | |----------------------+----------------| | 3.8.1 | Pending | +---------------------------------------+ Workarounds =========== There are no workarounds on the affected device itself. Co-ordination is required with the peering neighbor support staff to filter the invalid update on their outbound path. The following procedure explains how to help mitigate this vulnerability: Using the peer IP address in the log message that was generated when the Cisco IOS XR software device received the invalid update; capture the notification message hex dump from the CLI command show bgp neighbor and contact the Cisco TAC whom can assist with a decode. Details on how to contact Cisco TAC are contained within the section "Obtaining Fixed Software" of this advisory. The following example show an example generated log message when receiving the invalid update, and the details to be captured to be sent to the Cisco TAC for decoding: Log message generated when receiving invalid update: RP/0/RP0/CPU0:Aug 17 13:47:05.896 GMT: bgp[122]: %ROUTING-BGP-5-ADJCHANGE : neighbor 192.168.0.1 Down - BGP Notification sent: invalid or corrupt AS path Information to capture for decoding by the Cisco TAC, is the output from show bgp neighbors [ip address of neighbor from above log message]. RP/0/RP0/CPU0:CRS#show bgp neighbors 192.168.0.1 <capture output and provide to Cisco TAC> Working with Cisco TAC, the decode of the above will display the AS path in a manner illustrated below. ATTRIBUTE NAME: AS_PATH AS_PATH: Type 2 is AS_SEQUENCE AS_PATH: Segment Length is 4 (0x04) segments long AS_PATH: 65533 65532 65531 65531 Working cooperatively with your peering partner, request that they filter outbound prefix advertisements from the identified source AS (in this example 65531) for your peering session. The filters configuration methods will vary depending on the routing device operating system used. For Cisco IOS XR the filters will be applied using Routing Policy Language (RPL) policies or with Cisco IOS software via applying route-maps that deny advertisements matching that AS in their AS-PATH. Once these policies are applied, the peering session will be re-established. For further information on Cisco IOS XR RPL 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 For further information on Cisco IOS route maps with BGP, consult the document "Cisco IOS BGP Configuration Guide, Release 12.4T" at the following link: http://www.cisco.com/en/US/docs/ios/12_2sr/12_2srb/feature/guide/tbgp_c.html Obtaining Fixed Software
Cisco will be releasing free software updates that address this vulnerability. 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
On August 17, 2009 around 16:30-17:00 UTC several ISP's began experiencing connectivity issues as BGP sessions were being repeatedly reset. Cisco TAC was engaged with a number of customers all seeing similar issues. Stability came a few hours afterward as workarounds were applied. At this time, it is not believed that the connectivity issues were the result of malicious activity. 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-20090818-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 | 2009-August-18 | 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 - --------------------------------------------------------------------- -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.5 (Darwin) iD8DBQFKitOJ86n/Gc8U/uARAlpUAJ95EA/XmiFntl4XuXpKTpqeIt5q8gCfdOPV /OmnNTdlD9lueFh99gS6NDM= =dejJ -----END PGP SIGNATURE-----

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