Summary

• A vulnerability in the internal packet processing of Cisco Aironet Series Access Points (APs) could allow an unauthenticated, adjacent attacker to cause a denial of service (DoS) condition on an affected AP if the switch interface where the AP is connected has port security configured.

  The vulnerability exists because the AP forwards some malformed wireless client packets outside of the Control and Provisioning of Wireless Access Points (CAPWAP) tunnel. An attacker could exploit this vulnerability by sending crafted wireless packets to an affected AP. A successful exploit could allow the attacker to trigger a security violation on the adjacent switch port, which could result in a DoS condition.

  Note: Though the Common Vulnerability Scoring System (CVSS) score corresponds to a High Security Impact Rating (SIR), this vulnerability is considered Medium because a workaround is available and exploitation requires a specific switch configuration.

  There are workarounds that address this vulnerability.

  This advisory is available at the following link:
  https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190417-air-ap-dos

Affected Products

• Vulnerable Products

  This vulnerability affects the following Cisco products if they are running a vulnerable software release:

  • 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

  For information about affected software releases, consult the Cisco bug ID(s) at the top of this advisory.

  Products Confirmed Not Vulnerable

  Only products listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability.

Details

• This vulnerability is exploitable only if the switch port adjacent to the AP is configured with port security and set to shut down when a violation is detected. In that case, client traffic is not encapsulated in a CAPWAP tunnel, so the switch will learn additional MAC addresses on the switch interface where the AP is connected. Once the limit for MAC addresses is reached, a security violation is triggered.

  By default, port security is disabled. When it is enabled, shutdown is the default security violation mode.

Workarounds

• Administrators can configure the switch interface with port security to learn only one MAC address (the switch learns the AP MAC address during AP bootup) and, in case of a security violation, to drop any new learned MAC addresses. Using the CLI, configure the security violation mode to either protect or restrict, as in the following example:

  # configuration terminal
  # interface interface_id
  # switchport port-security violation {protect | restrict}

  Note: CLI commands may vary slightly by switch model.

Fixed Software

• For information about fixed software releases, consult the Cisco bug ID(s) at the top of this advisory.

  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.

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://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190417-air-ap-dos

Revision History

• Version	Description	Section	Status	Date
  1.1	Added bug ID with a more complete fix. Added Aironet 4800 APs and Catalyst 9100 APs to Affected Products due to change in impacted software versions.	Header, Vulnerable Products	Final	2020-MAY-11
  1.0	Initial public release.	—	Final	2019-APR-17

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