Summary

• A vulnerability in the IPv6 protocol handling of the management interfaces of Cisco IOS XR Software could allow an unauthenticated, adjacent attacker to cause an IPv6 flood on the management interface network of an affected device.

  The vulnerability exists because the software incorrectly forwards IPv6 packets that have an IPv6 node-local multicast group address destination and are received on the management interfaces. An attacker could exploit this vulnerability by connecting to the same network as the management interfaces and injecting IPv6 packets that have an IPv6 node-local multicast group address destination. A successful exploit could allow the attacker to cause an IPv6 flood on the corresponding network. Depending on the number of Cisco IOS XR Software nodes on that network segment, exploitation could cause excessive network traffic, resulting in network degradation or a denial of service (DoS) condition.

  Cisco has released software updates that address this vulnerability. There are workarounds that address this vulnerability.

  This advisory is available at the following link:
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-xripv6-spJem78K

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco devices if they are running a vulnerable release of Cisco IOS XR Software and the management interface is configured with both of the following:

  • An IPv6 address
  • The default IPv6 static route with next-hop on the management interface segment

  For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory.

  Products Confirmed Not Vulnerable

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

Details

• If this vulnerability is exploited, the number of packets that are forwarded to the network is dependent on the number of Cisco IOS XR Software management interfaces that are connected to the network segment. The more Cisco IOS XR devices that have management interfaces and are connected to the same Layer 2 domain, the more packets that are forwarded on the Layer 2 segment. An excessive number of forwarded packets could result in network degradation and possibly cause a denial of service (DoS) condition on the network.

Workarounds

• Removing the default IPv6 static route and adding a prefix-specific route would mitigate this vulnerability. For example, removing the default IPv6 static route and adding an IPv6 static route of 2000::/3 <next hop> would mitigate this vulnerability.

Fixed Software

• Cisco has released free software updates that address the vulnerability 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 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 fixed this vulnerability in Cisco IOS XR Software releases 6.7.3, 7.1.3, 7.2.2, and 7.3.1.

  Cisco has released software maintenance upgrades (SMUs) to address this vulnerability. Customers who require SMUs for other platforms and releases are advised to contact their support organization.

  Cisco IOS XR Software Release	Platform	SMU Name
  6.3.1	NCS1K	ncs1k-6.3.1.CSCvv45504
  	NCS1001	ncs1001-6.3.1.CSCvv45504
  6.5.2	NCS1K	ncs1k-6.5.2.CSCvv45504
  	NCS1001	ncs1001-6.5.2.CSCvv45504

   

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-xripv6-spJem78K

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2021-FEB-03

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