[apops] Cisco Security Advisory: Cisco Security Advisory: Cisco IOS XR S

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  • Subject: [apops] Cisco Security Advisory: Cisco Security Advisory: Cisco IOS XR Software Border Gateway Protocol Vulnerability
  • From: Cisco Systems Product Security Incident Response Team <psirt at cisco dot com>
  • Date: Tue, 18 Aug 2009 16:25:00 -0000
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      Cisco Security Advisory: Cisco Security Advisory: Cisco IOS XR
      Software Border Gateway Protocol Vulnerability
      Advisory ID: cisco-sa-20090818-bgp
      Revision 1.0
      For Public Release 2009 August 18 1500 UTC (GMT)
      - ---------------------------------------------------------------------
      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: 
      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 
      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: 
      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: 
      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
      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
           address-family ipv4 unicast
           address-family vpnv4 unicast
            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
      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 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
      Cisco has also provided a CVSS calculator to help compute the
      environmental impact for individual networks at
      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
      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        |
      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 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
          RP/0/RP0/CPU0:CRS#show bgp neighbors        
          <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.
           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: 
      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: 
      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
      or as otherwise set forth at Cisco.com Downloads at
      Do not contact psirt at cisco dot com or security-alert at cisco dot 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 at cisco dot 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
      for additional TAC contact information, including localized telephone
      numbers, and instructions and e-mail addresses for use in various
      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
      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.
      This advisory is 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
        * first-bulletins at lists dot first dot org
        * bugtraq at securityfocus dot com
        * vulnwatch at vulnwatch dot org
        * cisco at spot dot colorado dot edu
        * cisco-nsp at puck dot nether dot net
        * full-disclosure at lists.grok dot org dot uk
        * comp.dcom.sys.cisco at newsgate dot cisco dot 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
      This includes instructions for press inquiries regarding Cisco
      security notices.  All Cisco security advisories are available at
      - ---------------------------------------------------------------------
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