Summary

• A vulnerability in the Cisco Discovery Protocol implementation for Cisco NX-OS Software could allow an unauthenticated, adjacent attacker to execute arbitrary code or cause a reload on an affected device.

  The vulnerability exists because the Cisco Discovery Protocol parser does not properly validate input for certain fields in a Cisco Discovery Protocol message. An attacker could exploit this vulnerability by sending a malicious Cisco Discovery Protocol packet to an affected device. An successful exploit could allow the attacker to cause a stack overflow, which could allow the attacker to execute arbitrary code with administrative privileges on an affected device.

  Note: Cisco Discovery Protocol is a Layer 2 protocol. To exploit this vulnerability, an attacker must be in the same broadcast domain as the affected device (Layer 2 adjacent).

  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-20200205-nxos-cdp-rce

Affected Products

• Vulnerable Products

  This vulnerability affects the following Cisco products if they have Cisco Discovery Protocol enabled both globally and on at least one interface and if they are running a vulnerable release of Cisco NX-OS Software:

  • Nexus 3000 Series Switches
  • Nexus 9000 Series Fabric Switches in Application Centric Infrastructure (ACI) mode
  • Nexus 9000 Series Switches in standalone NX-OS mode

  Note: Cisco Discovery Protocol is enabled on these products by default both globally and on all interfaces.

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

  Determine the Status of Cisco Discovery Protocol for Cisco Nexus Switches That Are Running Cisco NX-OS Software

  Administrators can determine whether Cisco Discovery Protocol is enabled on a device by using the show running-config cdp all | include “cdp enable” command in the device CLI. If the command returns at least the following lines, Cisco Discovery Protocol is enabled globally and on at least one interface:

  nxos# show running-config cdp all | include "cdp enable"
  cdp enable
    cdp enable

  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 Switches¹
  • Nexus 5600 Platform Switches¹
  • Nexus 6000 Series Switches¹
  • Nexus 7000 Series Switches
  • UCS 6200 Series Fabric Interconnects¹
  • UCS 6300 Series Fabric Interconnects¹
  • UCS 6400 Series Fabric Interconnects¹

  1. Earlier versions of this security advisory reported Nexus 5500 Platform Switches, Nexus 5600 Platform Switches, Nexus 6000 Series Switches, and UCS 6200 Series, 6300 Series, and 6400 Series Fabric Interconnects as affected by this vulnerability. This information was incorrect.

  Cisco has also confirmed that this vulnerability does not affect Cisco IOS Software, Cisco IOS XE Software, or Cisco IOS XR Software.

Workarounds

• There are no workarounds that address this vulnerability.

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

  Disable Cisco Discovery Protocol Globally on Cisco Nexus Switches That Are Running Cisco NX-OS Software

  To disable Cisco Discovery Protocol globally on Cisco Nexus Switches that are running Cisco NX-OS Software, administrators can 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 Nexus Switches That Are Running Cisco NX-OS Software

  To disable Cisco Discovery Protocol on an interface on Cisco Nexus Switches that are running Cisco NX-OS Software, administrators can 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.

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 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

  In the following table(s), the left column lists Cisco software releases. The right 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.

  Nexus 3000 Series Switches and Nexus 9000 Series Switches in Standalone NX-OS Mode: CSCvr09175

  Cisco NX-OS Software Release	First Fixed Release for This Vulnerability
  Earlier than 7.0(3)I7	Not vulnerable
  7.0(3)I7	7.0(3)I7(8) (Feb 2020) or appropriate SMU1
  7.0(3)F2	Not vulnerable
  9.2	9.3(2)
  9.3	9.3(2)

  1. The SMUs that are available for Cisco NX-OS Software releases 7.0(3)I7(5a), 7.0(3)I7(6), and 7.0(3)I7(7) fix this vulnerability (CSCvr09175). They also fix the vulnerability (CSCvr14976) that is described in the advisory Cisco FXOS, IOS XR, and NX-OS Software Cisco Discovery Protocol Denial of Service Vulnerability. The SMU filename follow this format: CSCvr09175-n9k_ALL-1.0.0-<nx-os_release>.lib32_n9000.rpm.

  2. The Cisco NX-OS Software 7.0(3)F train runs only on Cisco Nexus 3600 Platform Switches and the Nexus 9500 R-Series Switching Platform and is no longer maintained. Customers are advised to migrate to Cisco NX-OS Software Release 9.2 or later.

  SMU Installation Instructions

  To download the SMUs from the Software Center on Cisco.com, do the following:

  1. Click Browse All.
  2. Choose IOS and NX-OS Software > NX-OS > NX-OS Software > Switches > Data Center Switches.
  3. Choose the appropriate product and model.
  4. Choose NX-OS Software Maintenance Upgrades (SMU).
  5. Choose a release from the left pane of the appropriate product page.

  Note: The SMU filename follow this format: CSCvr09175-n9k_ALL-1.0.0-<NX-OS_Release>.lib32_n9000.rpm. For example, the SMU filename for Cisco NX-OS Software Release 7.0(3)I7(6) is CSCvr09175-n9k_ALL-1.0.0-7.0.3.I7.6.lib32_n9000.rpm.

  To install the appropriate SMU, copy the SMU to the Bootflash: file system for the switch and execute the following commands, which activate the fix right away (this is a hot patch):

  1. install add bootflash:<SMU_filename> activate
  2. install commit

  The following example shows the commands for installing the SMU for Cisco NX-OS Software Release 7.0(3)I7(6):

  nx-os# install add bootflash:CSCvr09175-n9k_ALL-1.0.0-7.0.3.I7.6.lib32_n9000.rpm activate  
  nx-os# install commit  
  

  Note: These instructions apply to only this particular type of SMU.

  Nexus 9000 Series Fabric Switches in ACI Mode: CSCvr09531

  Cisco NX-OS Software Release	First Fixed Release for This Vulnerability
  Earlier than 13.1	Not vulnerable
  13.1	Not vulnerable
  13.2	Not vulnerable
  14.0	14.2(1j)
  14.1	14.2(1j)
  14.2	14.2(1j)

   

  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, 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 aware of public announcements about this vulnerability. Cisco PSIRT is not aware of any malicious use of the vulnerability that is described in this advisory.

Source

• Cisco would like to thank Barak Hadad of Armis for reporting this vulnerability.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20200205-nxos-cdp-rce

Revision History

• Version	Description	Section	Status	Date
  1.4	Updated that Cisco Nexus 5500 Platform Switches, Nexus 5600 Platform Switches and Nexus 6000 Series Switches are not affected by this vulnerability.	Vulnerable Products, Products Confirmed Not Vulnerable, Fixed Software	Final	2020-February-14
  1.3	Updated that Cisco UCS Fabric Interconnects are not affected by this vulnerability.	Vulnerable Products, Products Confirmed Not Vulnerable, Workarounds, Fixed Software	Final	2020-February-12
  1.2	Updated information on vulnerable releases for Nexus 3000 Series Switches and Nexus 9000 Series Switches.	Fixed Software	Final	2020-February-11
  1.1	Corrected information around when Cisco UCS Fabric Interconnects are vulnerable and mitigation options for Cisco UCS Fabric Interconnects.	Vulnerable Products, Workarounds	Final	2020-February-06
  1.0	Initial public release.	—	Final	2020-February-05

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