Summary

• A vulnerability in the Border Gateway Protocol (BGP) Multicast VPN (MVPN) implementation of Cisco NX-OS Software could allow an unauthenticated, remote attacker to cause an affected device to unexpectedly reload, resulting in a denial of service (DoS) condition.

  The vulnerability is due to incomplete input validation of a specific type of BGP MVPN update message. An attacker could exploit this vulnerability by sending this specific, valid BGP MVPN update message to a targeted device. A successful exploit could allow the attacker to cause one of the BGP-related routing applications to restart multiple times, leading to a system-level restart.

  Note: The Cisco implementation of BGP accepts incoming BGP traffic from only explicitly configured peers. To exploit this vulnerability, an attacker must send a specific BGP MVPN update message over an established TCP connection that appears to come from a trusted BGP peer. To do so, the attacker must obtain information about the BGP peers in the trusted network of the affected system.

  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-nxosbgp-nlri-dos-458rG2OQ

  This advisory is part of the August 2020 Cisco FXOS and NX-OS Software Security Advisory Bundled Publication, which includes seven Cisco Security Advisories that describe seven vulnerabilities. For a complete list of the advisories and links to them, see Cisco Event Response: August 2020 Cisco FXOS and NX-OS Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  This vulnerability affects the following Cisco products if they are running a vulnerable release of Cisco NX-OS Software and BGP with MVPN is configured:

  • Nexus 3000 Series Switches
  • Nexus 9000 Series Switches in standalone NX-OS mode

  The following conditions must be true for a device to be vulnerable:

  • The device has feature ngmvpn configured.
  • The device has at least one BGP neighbor (peer) configured.
  • The device has a BGP connection that is configured for MPVN under the BGP neighbor.

  Note: These switches process BGP packets on TCP port 179 on IPv4 and IPv6.

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

  Determine the Device Configuration

  To determine whether a Nexus device is configured with BGP and a BGP neighbor, use the show running-config | include mvpn CLI command from the NX-OS CLI. If the configuration keyword mvpn is present, BGP is enabled.

  The following example shows BGP enabled with MVPN:

  nxos# show running-config | include mvpn
  
  feature ngmvpn
  ...
  address-family ipv4 mvpn

  Note: The address-family ipv4|ipv6 mvpn CLI command must be configured under the neighbor section of the BGP configuration.

  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 the following Cisco products:

  • Firepower 1000 Series
  • Firepower 2100 Series
  • Firepower 4100 Series
  • Firepower 9300 Security Appliances
  • MDS 9000 Series Multilayer Switches
  • Nexus 1000 Virtual Edge for VMware vSphere
  • Nexus 1000V Switch for Microsoft Hyper-V
  • Nexus 1000V Switch for VMware vSphere
  • Nexus 5500 Platform Switches
  • Nexus 5600 Platform Switches
  • Nexus 6000 Series Switches
  • Nexus 7000 Series Switches
  • Nexus 9000 Series Fabric Switches in Application Centric Infrastructure (ACI) mode
  • UCS 6200 Series Fabric Interconnects
  • UCS 6300 Series Fabric Interconnects
  • UCS 6400 Series Fabric Interconnects

Workarounds

• There are no workarounds that address 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.

  Cisco NX-OS Software

  To help customers determine their exposure to vulnerabilities in Cisco NX-OS Software, Cisco provides the Cisco Software Checker to identify any Cisco Security Advisories that impact a specific Cisco NX-OS Software release and the earliest release that fixes the vulnerabilities that are described in each advisory (“First Fixed”). If applicable, the tool also returns the earliest release that fixes all the vulnerabilities described in all the advisories identified (“Combined First Fixed”).

  Customers can use the Cisco Software Checker to search advisories in the following ways:

  • Choose the software, platform, and one or more releases
  • Upload a .txt file that includes a list of specific releases
  • Enter the output of the show version command

  After initiating a search, customers can customize the search to include all Cisco Security Advisories or one or more specific advisories.

  Customers can also use the following form to determine whether a release is affected by any Cisco Security Advisory by choosing the Cisco NX-OS Software and platform and then entering a release-for example, 7.0(3)I7(5) for Cisco Nexus 3000 Series Switches or 14.0(1h) for Cisco NX-OS Software in ACI mode:

  Cisco NX-OS Software Cisco NX-OS Software in ACI Mode MDS 9000 Series Multilayer Switches Nexus 1000V Series Switches Nexus 3000 Series Switches Nexus 5000 Series Switches Nexus 6000 Series Switches Nexus 7000 Series Switches Nexus 9000 Series Switches

  By default, the Cisco Software Checker includes results only for vulnerabilities that have a Critical or High Security Impact Rating (SIR). To include results for Medium SIR vulnerabilities, customers can use the Cisco Software Checker and check the Medium check box in the drop-down list under Impact Rating when customizing a search.

  Additional Resources

  For help determining the best Cisco NX-OS Software release for a Cisco Nexus Switch, administrators can refer to the following Recommended Releases documents. If a security advisory recommends a later release, Cisco recommends following the advisory guidance.

  Cisco MDS Series Switches
  Cisco Nexus 1000V for VMware Switch
  Cisco Nexus 3000 Series Switches
  Cisco Nexus 5500 Platform Switches
  Cisco Nexus 5600 Platform Switches
  Cisco Nexus 6000 Series Switches
  Cisco Nexus 7000 Series Switches
  Cisco Nexus 9000 Series Switches
  Cisco Nexus 9000 Series ACI-Mode Switches

  To determine the best release for Cisco UCS Software, see the Recommended Releases documents in the release notes for the device.

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 by Hao Wu of Cisco during internal security testing.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-nxosbgp-nlri-dos-458rG2OQ

Revision History

• Version	Description	Section	Status	Date
  1.1	Fixed Software Checker link.	Fixed Software	Final	2020-AUG-26
  1.0	Initial public release.	-	Final	2020-AUG-26

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