Summary

• A vulnerability in the External Border Gateway Protocol (eBGP) implementation of Cisco NX-OS Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device.

  This vulnerability exists because eBGP traffic is mapped to a shared hardware rate-limiter queue. An attacker could exploit this vulnerability by sending large amounts of network traffic with certain characteristics through an affected device. A successful exploit could allow the attacker to cause eBGP neighbor sessions to be dropped, leading to a DoS condition in the network.

  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-nxos-ebgp-dos-L3QCwVJ

  This advisory is part of the February 2024 Cisco FXOS and NX-OS Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: February 2024 Semiannual Cisco FXOS and NX-OS Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco Nexus 3600 Series Switches and Cisco Nexus 9500 R-Series Line Cards if they are running a vulnerable release of Cisco NX-OS Software, they have BGP functionality with at least one BGP neighbor (peer) that is configured with a different Autonomous System (AS) value, and they have one of the following Cisco product IDs:

  • N3K-C36180YC-R
  • N3K-C3636C-R
  • N9K-X9624D-R2
  • N9K-X9636C-R
  • N9K-X9636C-RX
  • N9K-X9636Q-R
  • N9K-X96136YC-R

  Note: The list of affected Cisco Nexus 3600 Series Switch product IDs and Cisco Nexus 9500 R-Series Line Card product IDs was accurate at the time of publication. For specific questions about a product ID, contact the Cisco Technical Assistance Center (TAC).

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

  Determine Whether BGP is Enabled

  To determine whether a Cisco Nexus device is configured with the BGP feature and an eBGP neighbor, use the show running-config | include "router bgp" and show running-config | include "neighbor" commands from the Cisco NX-OS Software CLI and verify that the feature is enabled.

  The following example shows the BGP feature enabled with one eBGP neighbor on a device that is running Cisco NX-OS Software:

  nxos-switch# show running-config | include "router bgp"
  router bgp 1
  nxos-switch# show running-config | include "neighbor"
  neighbor 10.10.10.2 remote-as 2

   

  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 3000 Series Switches, other than the models referenced in Vulnerable Products
  • Nexus 5500 Platform Switches
  • Nexus 5600 Platform Switches
  • Nexus 6000 Series Switches
  • Nexus 7000 Series Switches
  • Nexus 9000 Series Fabric Switches in ACI mode
  • Nexus 9000 Series Switches in standalone NX-OS mode, other than the models referenced in Vulnerable Products
  • Secure Firewall 3100 Series
  • Secure Firewall 4200 Series
  • UCS 6200 Series Fabric Interconnects
  • UCS 6300 Series Fabric Interconnects
  • UCS 6400 Series Fabric Interconnects
  • UCS 6500 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 with service contracts that entitle them to regular software updates should obtain security fixes through their usual update channels.

  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.

  The Cisco Support and Downloads page on Cisco.com provides information about licensing and downloads. This page can also display customer device support coverage for customers who use the My Devices tool.

  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. This tool identifies any Cisco security advisories that impact a specific 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 that the Software Checker identifies (“Combined First Fixed”).

  To use the tool, go to the Cisco Software Checker page and follow the instructions. Alternatively, use the following form to search for vulnerabilities that affect a specific software release. To use the form, follow these steps:

  1. Choose which advisories the tool will search—only this advisory, only advisories with a Critical or High Security Impact Rating (SIR), or all advisories.
  2. Choose the appropriate software.
  3. Choose the appropriate platform.
  4. Enter a release number—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.
  5. Click Check.

   

  Only this advisory All Critical and High advisories All advisories Cisco NX-OS Software Cisco NX-OS Software in ACI Mode Any Platform 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

   

   

  Nexus 3600 Series Switches and Nexus 9500 R-Series Line Cards SMUs

  Cisco has released the following SMUs to address this vulnerability. Customers can download the SMUs from the Software Center on Cisco.com.

  Cisco NX-OS Software Release	Platform	SMU Name
  9.3(12)	Nexus 3600 Switches Nexus 9500 R-Series Line Cards	nxos.CSCwh09703-n9k_ALL-1.0.0-9.3.12.lib32_n9000.rpm
  10.2(6)	Nexus 3600 Switches Nexus 9500 R-Series Line Cards	nxos64-msll.CSCwh09703-1.0.0-10.2.6.lib32_64_n9000.rpm
  10.3(4a)	Nexus 9500 R-Series Line Cards1	nxos64-msll.CSCwh96478-1.0.0-10.3.4a.lib32_64_n9000.rpm

  1. Only the N9K-X9636C-RX line card is affected when running Release 10.3(4a). All other models are not affected in this particular software release. 

  For details about downloading and installing SMUs in Cisco NX-OS Software for Cisco Nexus 3600 and 9500 Switches, see the Performing Software Maintenance Upgrades section of the Cisco NX-OS system management configuration guide for Cisco Nexus 3000 Series Switches and Cisco Nexus 9000 Series Switches

  Additional Resources

  For help determining the best Cisco NX-OS Software release for a Cisco Nexus Switch, see 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 during the resolution of a Cisco TAC support case.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-nxos-ebgp-dos-L3QCwVJ

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2024-FEB-28

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