CVE-2022-20824: Cisco Security Advisory: Cisco FXOS and NX-OS Software Cisco Discovery Protocol Denial of Service and Arbitrary Code Execution Vulnerability

• There are no workarounds that address this vulnerability.

  However, customers who do not use Cisco Discovery Protocol can disable the feature either globally, to fully close the attack vector, or on individual interfaces, to reduce the attack surface.

  Disable Cisco Discovery Protocol in Cisco FXOS Software

  Cisco Discovery Protocol is always enabled and cannot be disabled in Cisco FXOS Software. In Cisco FXOS Software releases 2.1 and later, Cisco Discovery Protocol is enabled on the management (mgmt0) port only.

  Disable Cisco Discovery Protocol Globally on Cisco MDS and Nexus Switches that are Running Cisco NX-OS Software

  To disable Cisco Discovery Protocol globally on a Cisco MDS or Nexus Switch, use the no cdp enable command in global configuration mode, as shown in the following example:

  nxos# conf t Enter configuration commands, one per line. End with CNTL/Z. nxos(config)# no cdp enable nxos(config)# end nxos# copy running-config startup-config [########################################] 100% Copy complete.

**Disable Cisco Discovery Protocol on an Interface on Cisco MDS and Nexus Switches that are Running Cisco NX-OS Software**

To disable Cisco Discovery Protocol on an interface on a Cisco MDS or Nexus Switch, use the **no cdp enable** command in interface configuration mode, as shown in the following example:

> nxos# conf t
> Enter configuration commands, one per line. End with CNTL/Z.
> nxos(config)# interface Ethernet1/1
> nxos(config-if)# **no cdp enable** 
> nxos(config-if)# end
> nxos# copy running-config startup-config
> \[########################################\] 100%
> Copy complete.

  
**Disable Cisco Discovery Protocol on Cisco UCS Fabric Interconnects**

Cisco Discovery Protocol cannot be disabled completely on Cisco UCS Fabric Interconnects. Cisco Discovery Protocol can be disabled on server ports and appliance ports on Cisco UCS Fabric Interconnects, but it cannot be disabled on Ethernet uplink ports, Ethernet port channel members, FCoE uplink ports, or management ports.

To disable Cisco Discovery Protocol on the server ports of a Cisco UCS Fabric Interconnect, use the **disable cdp** command in the default **nw-ctrl-policy** in the **org** scope, as shown in the following example:

> ucs-fi# scope org
> ucs-fi /org # enter nw-ctrl-policy default
> ucs-fi /org/nw-ctrl-policy # **disable cdp**
> ucs-fi /org/nw-ctrl-policy\* # exit
> ucs-fi /org\* # exit
> ucs-fi\* # commit-buffer
> ucs-fi# 

To disable Cisco Discovery Protocol on the appliance ports of a Cisco UCS Fabric Interconnect, use the **disable cdp** command in the default **nw-ctrl-policy** in the **eth-storage** scope, as shown in the following example:

> ucs-fi\* # scope eth-storage
> ucs-fi /eth-storage\* # enter nw-ctrl-policy default
> ucs-fi /eth-storage/nw-ctrl-policy\* # **disable cdp**
> ucs-fi /eth-storage/nw-ctrl-policy\* # exit
> ucs-fi /eth-storage\* # exit
> ucs-fi\* # commit-buffer
> ucs-fi# 

While these mitigations have been deployed and were proven successful in a test environment, customers should determine the applicability and effectiveness in their own environment and under their own use conditions. Customers should be aware that any workaround or mitigation that is implemented may negatively impact the functionality or performance of their network based on intrinsic customer deployment scenarios and limitations. Customers should not deploy any workarounds or mitigations before first evaluating the applicability to their own environment and any impact to such environment.

• 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 FXOS and NX-OS Software

  To help customers determine their exposure to vulnerabilities in Cisco FXOS and 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 that are 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, 2.9.1.158 for Cisco Firepower 4100 Series Security Appliances or 7.0(3)I7(5) for Cisco Nexus 3000 Series Switches.
  5. Click Check.

**Cisco Nexus 3000, 7000, and 9000 Series Switches 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

8.2(8)

Nexus 7000 Series Switches

n7000-s2-dk9.8.2.8.CSCwc36631.bin  
n7700-s2-dk9.8.2.8.CSCwc36631.bin

9.3(9)

Nexus 3000 and 9000 Series Switches

nxos.CSCwb70210-n9k\_ALL-1.0.0-9.3.9.lib32\_n9000.rpm

For details about downloading and installing SMUs in Cisco NX-OS Software for Cisco Nexus 3000, 7000, and 9000 Series Switches, see the Performing Software Maintenance Upgrades section of the Cisco NX-OS system management configuration guide for Cisco Nexus 3000 Series Switches, Cisco Nexus 7000 Series Switches_,_ and Cisco Nexus 9000 Series Switches.

**Cisco UCS Software**

In the following table(s), the left column lists Cisco software releases. The center column indicates whether a release is affected by the vulnerability described in this advisory and the first release that includes the fix for this vulnerability. The right column indicates whether a release is affected by all of the High and Critical vulnerabilities described in this bundle and which release includes fixes for those vulnerabilities.

**UCS 6200, 6300, and 6400 Series Fabric Interconnects**

Cisco UCS Software Release

First Fixed Release for This Vulnerability

First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories

Earlier than 4.1

Migrate to a fixed release.

Migrate to a fixed release.

4.1

4.1(3i)

4.1(3i)

4.2

4.2(1n)

4.2(1n)

The Cisco Product Security Incident Response Team (PSIRT) validates only the affected and fixed release information that is documented in this advisory.

**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.