Summary

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

  The vulnerabilities are due to incorrect processing of BGP update messages that contain crafted EVPN attributes. An attacker could exploit these vulnerabilities by sending BGP EVPN update messages with malformed attributes 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 these vulnerabilities, 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 these vulnerabilities. There are no workarounds that address these vulnerabilities.

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

Affected Products

• Vulnerable Products

  These vulnerabilities affect Cisco devices if they are running a vulnerable release of Cisco IOS XR Software later than 6.6.1 and are configured for BGP on a device with the L2VPN EVPN address family. Some device EVPN configurations, such as the load-balancing-mode port-active configuration, can also cause devices to be vulnerable without specific L2VPN configurations.

  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
  
  .
  .
  .

  To determine whether the device is configured for the EVPN address family, administrators can use the show running-config router bgp AS-Number address-family l2vpn evpn EXEC command in the CLI. If the router is configured for the BGP EVPN address family, this command will return output.

  The following example shows the partial output of the show running-config router bgp AS-Number address-family l2vpn evpn command on a device with the EVPN address family configured:

  # show running-config router bgp 65536 address-family l2vpn evpn

  router bgp 100
  
  address-family l2vpn evpn
  
  .
  .
  .

  To determine whether the device has the EVPN configuration, administrators can use the show running-config l2vpn and show running-config evpn EXEC commands in the CLI. If the device is a provider edge router for EVPN, this command will return output.

  The following examples show the show running-config l2vpn  and show running-config evpn commands on a provider edge EVPN device:

  # show running-config l2vpn
  
  l2vpn
  
   bridge group <bridge_group>
  
    bridge-domain <bridge_domain>
  
  .
  .
  .

     interface <>
  
     evi <evi>
  
     !
  
    !
  
  !
  
  .
  .
  .
  

  # show running-config evpn
  
  evpn
  
     interface <interface>
  
    ethernet-segment
  
      identifier type <type and Ethernet Segment Identifier>
  
  .
  .
  .

  Products Confirmed Not Vulnerable

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

  Cisco has confirmed that these vulnerabilities do not affect Cisco IOS Software, Cisco IOS XE Software, or Cisco NX-OS Software.

Details

• Ethernet VPN (EVPN) is a next-generation solution that provides Ethernet multipoint services over MPLS networks. Customers can learn more about EVPN and configuration options in guides such as the L2VPN and Ethernet Services Configuration Guide for Cisco ASR 9000 Series Routers and in guides for other platforms that support this feature.

Workarounds

• There are no workarounds that address these vulnerabilities.

Fixed Software

• Cisco has released free software updates that address the vulnerabilities described in this advisory. Customers may only install and expect support for software versions and feature sets for which they have purchased a license. By installing, downloading, accessing, or otherwise using such software upgrades, customers agree to follow the terms of the Cisco software license:
  https://www.cisco.com/c/en/us/products/end-user-license-agreement.html

  Additionally, customers may only download software for which they have a valid license, procured from Cisco directly, or through a Cisco authorized reseller or partner. In most cases this will be a maintenance upgrade to software that was previously purchased. Free security software updates do not entitle customers to a new software license, additional software feature sets, or major revision upgrades.

  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.

  Customers Without Service Contracts

  Customers who purchase directly from Cisco but do not hold a Cisco service contract and customers who make purchases through third-party vendors but are unsuccessful in obtaining fixed software through their point of sale should obtain upgrades by contacting the Cisco TAC:
  https://www.cisco.com/c/en/us/support/web/tsd-cisco-worldwide-contacts.html

  Customers should have the product serial number available and be prepared to provide the URL of this advisory as evidence of entitlement to a free upgrade.

  Fixed Releases

  Cisco will fix these vulnerabilities in Cisco IOS XR Software Releases 6.6.3, 7.0.2, and 7.1.1.

  At 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 vulnerabilities described in this advisory were provided in the fixes 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.
  

  To download the software 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 a specific product 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 vulnerabilities that are described in this advisory.

Source

• These vulnerabilities were found by Mrinmoy Ghosh of Cisco during internal security testing.

URL

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

Revision History

• Version	Description	Section	Status	Date
  1.1	Included information regarding additional configurations that may expose the vulnerabilities in this advisory.	Affected Products	Final	2020-February-07
  1.0	Initial public release.	—	Final	2020-January-22

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