Summary

• A vulnerability in the implementation of the cluster feature of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, adjacent attacker to trigger a denial of service (DoS) condition on an affected device.

  The vulnerability is due to improper input validation when handling Cluster Management Protocol (CMP) messages. An attacker could exploit this vulnerability by sending a malicious CMP message to an affected device. A successful exploit could allow the attacker to cause the switch to crash and reload or to hang, resulting in a DoS condition. If the switch hangs it will not reboot automatically, and it will need to be power cycled manually to recover.

  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-20180926-cmp

  This advisory is part of the September 26, 2018, release of the Cisco IOS and IOS XE Software Security Advisory Bundled Publication, which includes 12 Cisco Security Advisories that describe 13 vulnerabilities. For a complete list of the advisories and links to them, see Cisco Event Response: September 2018 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco Catalyst Switches that are running a vulnerable release of Cisco IOS Software or Cisco IOS XE Software with the cluster feature enabled that have not been a cluster member since the last reload. On some platforms, the cluster feature is enabled by default. A switch with the cluster feature enabled is vulnerable only if it has not been a cluster member since the last reload.

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

  Determining Whether the Cluster Feature Is Enabled in a Vulnerable Way

  There are two methods for determining whether the cluster feature is enabled in a vulnerable way.

  Option 1: Using the show cluster Command

  To determine the status of the Cluster feature on a device, use the show cluster privileged EXEC command on the device. The following example shows the output of the show cluster command on a Cisco Catalyst Switch that has the cluster feature enabled but has not been a cluster member since the last reload:

  SWITCH1#show cluster
  % Not a management cluster member

  This is the only output of the show cluster command that indicates that the device is vulnerable.

  If this command does not exist, or if it produces any other output, the device is not affected by the vulnerability described in this advisory.

  Option 2: Using the show running-config [all] Command

  To determine whether a device is configured with the cluster feature enabled, use the show running-config all | include cluster run privileged EXEC command on the device. The following example shows the output of the show running-config all | include cluster run command on a switch that has the cluster feature enabled:

  SWITCH2#show running-config all | include cluster run
   cluster run

  To determine whether a device has been a cluster member since the last reload, use the show running-config | include cluster commander privileged EXEC command on the device. The following example shows the output of the show running-config | include cluster commander command on a switch that has been a cluster member since the last reload. On a switch that has not been a cluster member since the last reload, this command would result in empty output.

  SWITCH2#show running-config | include cluster commander
  cluster commander-address 0001.0001.0001

  When Option 2 is used to assess the device, it is affected by the vulnerability described in this advisory only if both the following conditions are true:

  • The output of the show running-config all command includes cluster run
  • The show running-config | include cluster commander command results in empty output

  Determining the Cisco IOS Software Release

  To determine which Cisco IOS Software release is running on a device, administrators can log in to the device, use the show version command in the CLI, and then refer to the system banner that appears. If the device is running Cisco IOS Software, the system banner displays text similar to Cisco Internetwork Operating System Software or Cisco IOS Software. The banner also displays the installed image name in parentheses, followed by the Cisco IOS Software release number and release name. Some Cisco devices do not support the show version command or may provide different output.

  The following example shows the output of the command for a device that is running Cisco IOS Software Release 15.5(2)T1 and has an installed image name of C2951-UNIVERSALK9-M:

  Router> show version
  
  Cisco IOS Software, C2951 Software (C2951-UNIVERSALK9-M), Version 15.5(2)T1, RELEASE SOFTWARE (fc1)
  Technical Support: http://www.cisco.com/techsupport
  Copyright (c) 1986-2015 by Cisco Systems, Inc.
  Compiled Mon 22-Jun-15 09:32 by prod_rel_team
  .
  .
  .

  For information about the naming and numbering conventions for Cisco IOS Software releases, see the Cisco IOS and NX-OS Software Reference Guide.

  Determining the Cisco IOS XE Software Release

  To determine which Cisco IOS XE Software release is running on a device, administrators can log in to the device, use the show version command in the CLI, and then refer to the system banner that appears. If the device is running Cisco IOS XE Software, the system banner displays Cisco IOS Software, Cisco IOS XE Software, or similar text.

  The following example shows the output of the command for a device that is running Cisco IOS XE Software Release 16.2.1 and has an installed image name of CAT3K_CAA-UNIVERSALK9-M:

  ios-xe-device# show version
  
  Cisco IOS Software, Catalyst L3 Switch Software (CAT3K_CAA-UNIVERSALK9-M), Version Denali 16.2.1, RELEASE SOFTWARE (fc1)
  Technical Support: http://www.cisco.com/techsupport
  Copyright (c) 1986-2016 by Cisco Systems, Inc.
  Compiled Sun 27-Mar-16 21:47 by mcpre
  .
  .
  .

  For information about the naming and numbering conventions for Cisco IOS XE Software releases, see the Cisco IOS and NX-OS Software Reference Guide.

  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 Cisco IOS XR Software or Cisco NX-OS Software.

Workarounds

• Manually configuring an arbitrary cluster command switch MAC address using the cluster commander-address mac_address command in global configuration mode prevents exploitation of this vulnerability.

  Administrators who do not use the cluster feature in their environments can also disable the cluster feature by using the no cluster run command in global configuration mode to mitigate this issue.

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.

  Cisco IOS and IOS XE Software

  To help customers determine their exposure to vulnerabilities in Cisco IOS and IOS XE Software, Cisco provides a tool, the Cisco IOS Software Checker, that identifies any Cisco Security Advisories that impact a specific software release and the earliest release that fixes the vulnerabilities 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 this tool to perform the following tasks:

  • Initiate a search by choosing one or more releases from a drop-down list or uploading a file from a local system for the tool to parse
  • Enter the output of the show version command for the tool to parse
  • Create a custom search by including all previously published Cisco Security Advisories, a specific advisory, or all advisories in the most recent bundled publication

  To determine whether a release is affected by any published Cisco Security Advisory, use the Cisco IOS Software Checker on Cisco.com or enter a Cisco IOS Software or Cisco IOS XE Software release—for example, 15.1(4)M2 or 3.13.8S—in the following field:

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

  For a mapping of Cisco IOS XE Software releases to Cisco IOS Software releases, refer to the Cisco IOS XE 2 Release Notes, Cisco IOS XE 3S Release Notes, or Cisco IOS XE 3SG Release Notes, depending on the Cisco IOS XE Software release.

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

• Cisco would like to thank Dmitry Kuznetsov of Digital Security for reporting this vulnerability.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180926-cmp

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2018-September-26

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