Summary

• A vulnerability in the AppNav-XE feature of Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause an affected device to reload, resulting in a denial of service (DoS) condition. 

  This vulnerability is due to the incorrect handling of certain TCP segments. An attacker could exploit this vulnerability by sending a stream of crafted TCP traffic at a high rate through an interface of an affected device. That interface would need to have AppNav interception enabled. A successful exploit could allow the attacker to cause the device to reload.

  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-appnav-xe-dos-j5MXTR4

  This advisory is part of the April 2022 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: April 2022 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  This vulnerability affects the following Cisco products if they are running a vulnerable release of Cisco IOS XE Software and have the AppNav-XE feature enabled:

  • 1000 Series Integrated Services Routers
  • 4000 Series Integrated Services Routers
  • ASR 1001-X Routers
  • ASR 1002-X Routers
  • Catalyst 8300 Series Routers
  • Catalyst 8500 Series Routers
  • Catalyst 8000V Edge Software
  • Cloud Services Router 1000V Series

  Note: The AppNav-XE feature is disabled by default in Cisco IOS XE Software.

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

  Determine the AppNav-XE Configuration

  To determine the AppNav-XE configuration, first verify that all of the following are true:

  • AppNav interception is enabled on at least one interface
  • An AppNav Controller group is configured and has at least one AppNav Controller member
  • A service node group is configured and has at least one service node member
  • A service context of type waas is configured, enabled, and links to an AppNav Controller group, a service node group, and a service policy

  To determine whether AppNav interception is enabled on at least one interface, use either of the following options:

  • Use the show running-config | include ^interface|service-insertion waas CLI command and confirm that service-insertion waas is configured under at least one interface. The following example shows the output on a device that has AppNav interception enabled on interface GigabitEthernet1:
    

    Router#show running-config | include ^interface|service-insertion waas
    interface VirtualPortGroup0
    interface GigabitEthernet1
     service-insertion waas
    interface GigabitEthernet2
    Router#

  • Use the show service-insertion status | begin AppNav Enabled Interfaces CLI command and confirm that at least one interface is listed in the resulting output. The following example shows the output on a device that has the AppNav-XE feature enabled on interface GigabitEthernet1:
    

    Router#show service-insertion status | begin AppNav Enabled Interfaces
    AppNav Enabled Interfaces: 
    GigabitEthernet1
    
    Router#

  To determine whether an AppNav Controller group, a service node group, and a service context of type waas are configured and enabled, use the show running-config | section service-insertion CLI command. The following example shows the output on a device that fulfills all of the requirements:

  Router#show running-config | section service-insertion
  service-insertion service-node-group WNG-Default-1
   service-node 192.168.100.102
   service-node 192.168.100.2
  service-insertion appnav-controller-group scg
   appnav-controller 192.168.10.10
  service-insertion service-context waas/1
   appnav-controller-group scg
   service-node-group WNG-Default-1
   service-policy APPNAV-1-PMAP
   vrf default
   enable
   service-insertion waas
  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 this vulnerability does not affect the following Cisco products:

  • AppNav Controllers running Cisco Wide Area Application Services (WAAS) Software
  • IOS Software
  • IOS XR Software
  • Meraki products
  • NX-OS Software

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 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-appnav-xe-dos-j5MXTR4

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2022-APR-13

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