Summary

• A vulnerability in the multicast DNS (mDNS) gateway feature of Cisco Aironet Series Access Points Software could allow an unauthenticated, adjacent attacker to cause a denial of service (DoS) condition on an affected device.

  This vulnerability is due to insufficient input validation of incoming mDNS traffic. An attacker could exploit this vulnerability by sending a crafted mDNS packet to an affected device through a wireless network that is configured in FlexConnect local switching mode or through a wired network on a configured mDNS VLAN. A successful exploit could allow the attacker to cause the access point (AP) to reboot, resulting in a DoS condition.

  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-aironet-mdns-dos-E6KwYuMx

Affected Products

• Vulnerable Products

  This vulnerability affects the following Cisco products if they are running a vulnerable release of Cisco Aironet Series Access Points Software, they have at least one wireless network configured in FlexConnect local switching mode, and the mDNS gateway feature is enabled on the wireless controller for that wireless network or one of the wired VLANs associated to it:

  • Aironet 1540 Series APs
  • Aironet 1560 Series APs
  • Aironet 1800 Series APs
  • Aironet 2800 Series APs
  • Aironet 3800 Series APs
  • Aironet 4800 APs
  • Catalyst 9100 APs
  • Catalyst IW 6300 APs
  • Integrated AP on 1100 Integrated Services Routers
  • 6300 Series Embedded Services APs (ESW6300)

  Determine the Status of FlexConnect Local Switching Mode

  To determine whether a wireless network is running in FlexConnect local switching mode, complete the following steps:

  1. Access the wireless controller management web interface.
  2. Choose Configuration > Tags & Profiles > Policy and open the profile that is associated to the wireless network.
  3. In the General tab, check the status of the Central Switching parameter.

  If Central Switching is disabled, the network is running in FlexConnect local switching mode

  Determine the Status of the mDNS Gateway feature

  To determine whether the mDNS Gateway is enabled on a wireless network, complete the following steps:

  1. Access the wireless controller management web interface.
  2. Choose Configuration > Tags & Profiles > WLANs and select the wireless network.
  3. On the Advanced tab, check the value selected in the mDNS Mode drop-down list.

  To determine whether the mDNS Gateway is enabled on a wired VLAN, complete the following steps:

  1. Access the wireless controller management web interface.
  2. Choose Configuration > Services > mDNS.
  3. In the mDNS Flex Profile section, click the profile name.
  4. Check the VLANs field to see which VLANs it is enabled for.

   

  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 any Cisco Access Point series that is not listed in the Vulnerable Products section of this advisory.

  Cisco has also confirmed that this vulnerability does not affect Cisco Wireless Controller and Cisco Mobility Express because they do not support enabling the mDNS Gateway feature on a FlexConnect wireless network.

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 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.

  Fixed Releases

  The process to upgrade the APs requires administrators to upgrade the wireless controller that the APs are registered to.

  Customers are advised to upgrade to an appropriate fixed software release as indicated in the following table(s). To ensure a complete upgrade solution, consider that this advisory is part of a collection that includes the following advisories:

  • cisco-sa-aironet-info-disc-BfWqghj: Cisco Aironet Access Points FlexConnect Upgrade Information Disclosure Vulnerability
  • cisco-sa-aironet-mdns-dos-E6KwYuMx: Cisco Aironet Access Points FlexConnect Multicast DNS Denial of Service Vulnerability
  • cisco-sa-ap-privesc-wEVfp8Ud: Cisco Access Point Software Arbitrary Code Execution Vulnerability

  Cisco Access Points Managed by Catalyst 9800 Wireless Controller or Embedded Wireless Controller on Catalyst Access Points

  Cisco Catalyst 9800 Wireless Controller Software Release	First Fixed Release for This Vulnerability	First Fixed Release for All Vulnerabilities Described in This Collection of Advisories
  17.2 and earlier	Not vulnerable.	Migrate to a fixed release.
  17.3	17.3.3	17.3.3
  17.4	Migrate to a fixed release.	17.5.1 (Mar 2021)
  17.5 and later	Not vulnerable.	Not vulnerable.

  Cisco Access Points Managed by Wireless LAN Controller or Mobility Express

  Cisco Wireless Controller and Cisco Mobility Express do not support enabling the mDNS Gateway feature on a FlexConnect wireless network, so these access points are not affected by this vulnerability.

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 internal security testing.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-aironet-mdns-dos-E6KwYuMx

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2021-MAR-24

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