Summary

• A vulnerability in the implementation of the Border Gateway Protocol (BGP) functionality in Cisco IOS XR Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition.

  The vulnerability is due to incorrect processing of a BGP update message that contains a specific BGP attribute. An attacker could exploit this vulnerability by sending BGP update messages that include a specific, malformed attribute to be processed by an affected system. A successful exploit could allow the attacker to cause the BGP process to restart unexpectedly, resulting in a DoS condition.

  The Cisco implementation of BGP accepts incoming BGP traffic only from explicitly defined peers. To exploit this vulnerability, the malicious BGP update message would need to come from a configured, valid BGP peer or would need to be injected by the attacker into the victim’s BGP network on an existing, valid TCP connection to a BGP peer.

  Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.

  This advisory is available at the following link:
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20200122-ios-xr-bgp-dos

Affected Products

• Vulnerable Products

  At the time of publication, this vulnerability affected Cisco devices if they running a vulnerable release of Cisco IOS XR Software and are configured for BGP.

  Cisco has confirmed that this vulnerability affects both Cisco IOS XR 32-bit Software and Cisco IOS XR 64-bit Software.

  For information about which Cisco IOS XR Software releases were vulnerable at the time of publication, see the Fixed Software section of this advisory.

  Determine Whether the Device Has a Vulnerable Configuration

  To determine whether the device is configured for BGP, administrators can use the show running-config router bgp EXEC command in the CLI. If the router is configured for BGP, this command will return output. The following example shows the partial output of the show running-config router bgp command on a device that is configured for BGP.

  #show running-config router bgp
  router bgp 65536
  …

  Products Confirmed Not Vulnerable

  Only products listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability.

  Cisco has confirmed that this vulnerability does not affect Cisco IOS Software, Cisco IOS XE Software, or Cisco NX-OS Software.

Details

• The specific, malformed BGP update attribute that can allow this vulnerability to be exploited is a non-transitive attribute. This means that this vulnerability affects only Interior BGP (iBGP). The bad attribute would be dropped at Autonomous System (AS) boundaries and could not be transmitted through Exterior BGP (eBGP).

Workarounds

• There are no workarounds that address this vulnerability.

Fixed Software

• When considering software upgrades, customers are advised to regularly consult the advisories for Cisco products, which are available from the Cisco Security Advisories and Alerts page, to determine exposure and a complete upgrade solution.

  In all cases, customers should ensure that the devices to be upgraded contain sufficient memory and confirm that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, customers are advised to contact the Cisco Technical Assistance Center (TAC) or their contracted maintenance providers.

  Fixed Releases

  At the time of publication, Cisco planned to fix this vulnerability in Cisco IOS XR Software releases 7.0.2, 7.1.1, and 7.2.1.

  At the time of publication, the SMUs in the following table were available. Customers who require SMUs for other platforms and releases are advised to contact their support organization.

  IOS XR Release	Platform	SMU Name1
  6.6.1	NCS5500	ncs5500-6.6.1.CSCvr91660
  6.6.1	ASR9K-X64	asr9k-x64-6.6.1.CSCvr91660
  6.6.1	NCS540	ncs540-6.6.1.CSCvr91660
  6.6.1	NCS6K	ncs6k-6.6.1.CSCvr91660
  6.6.2	ASR9K	asr9k-px-6.6.2.CSCvr91676
  6.6.2	ASR9K-X64	asr9k-x64-6.6.2.CSCvr91676
  6.6.2	CRS
  6.6.2	NCS5K
  6.6.2	XRV9K	xrv9k-6.6.2.CSCvr91676
  6.6.25	NCS540
  6.6.25	NCS540L
  6.6.25	NCS560	ncs560-6.6.25.CSCvr91676
  6.6.25	NCS5500	ncs5500-6.6.25.CSCvr91676
  7.0.1	ASR9K-X64	asr9k-x64-7.0.1.CSCvr91676
  7.0.1	NCS1K
  7.0.1	NCS5K
  7.0.1	NCS6K
  7.0.1	NCS540
  7.0.1	NCS540L
  7.0.1	NCS560
  7.0.1	NCS5500
  7.0.1	XRV9K

  1. Fixes for the vulnerability described in this advisory were provided in the fix for CSCvr91660 and CSCvr91676.
  

  CSCvr91660 includes the fixes for CSCvr84254, CSCvr74986, CSCvr74413, CSCvr80793, CSCvr83742, CSCvr74902, CSCvo90073, and CSCvr69950.

  CSCvr91676 includes the fixes for CSCvr84254, CSCvr74986, CSCvr74413, CSCvr80793, CSCvr83742, CSCvr74902, and CSCvr69950.

  For information about fixed software releases, see the Details section in the bug ID(s) at the top of this advisory.

  To download the SMUs from the Software Center on Cisco.com, do the following:

  1. Click Browse All.
  2. Choose IOS and NX-OS Software > IOS XR > IOS XR Software > Optical Networking or Routers.
  3. Choose the appropriate product and model from the right pane of the product selector.
  4. Choose a release from the left pane of the product page.

Exploitation and Public Announcements

• The Cisco Product Security Incident Response Team (PSIRT) is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.

Source

• This vulnerability was found during the resolution of a Cisco TAC support case.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20200122-ios-xr-bgp-dos

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2020-January-22

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