Summary

• A vulnerability in the Layer 2 punt code of Cisco IOS XE Software could allow an unauthenticated, adjacent attacker to cause a queue wedge on an interface that receives specific Layer 2 frames, resulting in a denial of service (DoS) condition.

  This vulnerability is due to improper handling of certain Layer 2 frames. An attacker could exploit this vulnerability by sending specific Layer 2 frames on the segment the router is connected to. A successful exploit could allow the attacker to cause a queue wedge on the interface, resulting in a DoS condition.

  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-quewedge-69BsHUBW

  This advisory is part of the September 2021 release of the Cisco IOS and IOS XE Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: September 2021 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco IOS XE Software if it is running on one of the following Cisco products:

  • 1000 Integrated Services Routers (ISRs)
  • 4000 Series ISRs
  • ASR 1000 Series Aggregation Services Routers
  • Cloud Services Router (CSR) 1000V Series
  • Integrated Services Virtual (ISRv) Routers

  In addition, if the device is running Cisco IOS XE Software Release 17.3.1 or a later release that is earlier than the first fixed release, the device is considered vulnerable.

  If the device is running a Cisco IOS XE Software release earlier than Release 17.3.1, it is considered vulnerable only if it does not support Autonomic Networking.

  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 device does not support Autonomic Networking, use the show running-config all | include autonomic command in the CLI. The following example shows the output of the command for a device that is running Cisco IOS XE Software and does not support Autonomic Networking:

  Router# show running-config all | include autonomic
  Router#

  The following example shows the output if a device supports Autonomic Networking:

  Router# show running-config all | include autonomic 
  autonomic
  autonomic
  autonomic
  Router#

   

  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 these vulnerabilities do not affect the following Cisco products:

  • IOS Software
  • IOS XR Software
  • Meraki products
  • NX-OS Software

Workarounds

• If a device is running a Cisco IOS XE Software release earlier than Release 17.3.1, changing the license level to one that supports Autonomic Networking, such as adventerprise, can be used as a workaround. If the device is running Cisco IOS XE Software Release 17.3.1 or later, there are no workarounds that address this vulnerability.

  If this vulnerability has been exploited and the attack has stopped, administrators can set a maximum hold-queue value that is greater than the currently configured value for the affected interface to allow traffic to pass until a reload can be scheduled. The following example shows how to set the value to 350 by using the hold-queue in interface configuration command:

  Router# configure terminal
  Router(config)# interface gigabitEthernet 1
  Router(config-if)# hold-queue 350 in

  Cisco IOS Embedded Event Manager

  A Cisco IOS Embedded Event Manager (EEM) policy that is based on Tool Command Language (Tcl) can be used on affected devices running Cisco IOS Software to detect and identify interface queue wedges that are caused by this vulnerability. The policy allows administrators to monitor interfaces for devices running Cisco IOS Software and detect when input queues are full. When Cisco IOS EEM detects potential exploitation of this vulnerability, the policy sends an alert to the network administrator, who can then decide to implement an upgrade, implement suitable mitigations, or reload the device to clear the input queue.

  The Tcl script is available for download at the following link: https://supportforums.cisco.com/docs/DOC-19337

  While this workaround has been deployed and was 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.

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 IOS and IOS XE Software

  To help customers determine their exposure to vulnerabilities in Cisco IOS and IOS XE Software, Cisco provides the Cisco Software Checker to identify 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 the Cisco Software Checker to search advisories in the following ways:

  • Choose the software 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, a specific advisory, or all advisories in the most recent bundled publication.

  Customers can also use the following form to determine whether a release is affected by any Cisco Security Advisory by entering a Cisco IOS or IOS XE Software release—for example, 15.1(4)M2 or 3.13.8S:

  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 on Cisco.com and check the Medium check box in the drop-down list under Impact Rating when customizing a search.

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-quewedge-69BsHUBW

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2021-SEP-22

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