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 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 https://sec.cloudapps.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.

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.

Fixed Software

• 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 

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.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20100827-bgp

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

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