Summary

• A vulnerability in the remote access VPN feature of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. 

  This vulnerability is due to improper handling of HTTPS requests. An attacker could exploit this vulnerability by sending crafted HTTPS requests to an affected system. A successful exploit could allow the attacker to cause resource exhaustion, 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-asa-webvpn-dos-3GhZQBAS

  This advisory is part of the November 2023 release of the Cisco ASA, FTD, and FMC Security Advisory Bundled publication. For a complete list of the advisories and links to them, see Cisco Event Response: November 2023 Semiannual Cisco ASA, FMC, and FTD Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  This vulnerability affects the following Cisco products:

  • ASA Software when it has Cisco AnyConnect Remote Access VPN or Clientless SSL VPN enabled
  • FTD Software when it has Cisco AnyConnect Remote Access VPN enabled

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

  Determine the Cisco ASA Software Configuration

  To determine whether Cisco ASA Software has a vulnerable feature enabled, use the show-running-config CLI command.

  In the following table, the left column lists Cisco ASA Software features that are vulnerable. The right column indicates the basic configuration for each feature from the show running-config CLI command. If a device is running a vulnerable release and has one of these features enabled, it is vulnerable:

  Cisco ASA Software Feature	Vulnerable Configuration
  AnyConnect Internet Key Exchange Version 2 (IKEv2) Remote Access (with client services)	crypto ikev2 enable client-services port
  AnyConnect SSL VPN	webvpn enable
  Clientless SSL VPN	webvpn enable

   

  Determine the Cisco FTD Software Configuration

  To determine whether Cisco FTD Software has a vulnerable feature enabled, use the show-running-config CLI command.

  In the following table, the left column lists Cisco FTD Software features that are vulnerable. The right column indicates the basic configuration for each feature from the show running-config CLI command. If a device is running a vulnerable release and has one of these features enabled, it is vulnerable:

  Cisco FTD Feature	Vulnerable Configuration
  AnyConnect IKEv2 Remote Access (with client services)1,2	crypto ikev2 enable client-services port
  AnyConnect SSL VPN1,2	webvpn enable

  1. Remote Access VPN features were introduced in Cisco FTD Software Release 6.2.2.

  2. Remote Access VPN features can be enabled using Devices > VPN > Remote Access in Cisco Firepower Management Center (FMC) or using Device > Remote Access VPN in Cisco Firepower Device Manager (FDM).

  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 Firepower Management Center (FMC) Software.

  Cisco has also confirmed that this vulnerability does not affect devices that have remote access VPN services configured to accept only Cisco AnyConnect IKEv2 Remote Access VPNs that have client services disabled.

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 ASA, FMC, and FTD Software

  To help customers determine their exposure to vulnerabilities in Cisco ASA, FMC, and FTD Software, Cisco provides the Cisco Software Checker. This tool identifies any Cisco security advisories that impact a specific software release and the earliest release that fixes the vulnerabilities that are described in each advisory (“First Fixed”). If applicable, the tool also returns the earliest release that fixes all the vulnerabilities that are described in all the advisories that the Software Checker identifies (“Combined First Fixed”).

  To use the tool, go to the Cisco Software Checker page and follow the instructions. Alternatively, use the following form to search for vulnerabilities that affect a specific software release. To use the form, follow these steps:

  1. Choose which advisories the tool will search—all advisories, only advisories with a Critical or High Security Impact Rating (SIR), or only this advisory.
  2. Choose the appropriate software.
  3. Choose the appropriate platform.
  4. Enter a release number—for example, 9.16.2.11 for Cisco ASA Software or 6.6.7 for Cisco FTD Software.
  5. Click Check.

  Only this advisory All Critical and High advisories All advisories Cisco ASA Software Cisco FMC Software Cisco FTD Software Any Platform 3000 Series Industrial Security Appliances (ISA) ASA 5500-X Series Firewalls ASA Service Module Adaptive Security Virtual Appliance (ASAv) Firepower 1000 Series Firepower 2100 Series Firepower 4100 Series Firepower 9000 Series Secure Firewall 3100 Series

   

  For instructions on upgrading your FTD device, see Cisco Firepower Management Center Upgrade Guide.

  Additional Resources

  For help determining the best Cisco ASA, FTD, or FMC Software release, see the following Recommended Releases documents. If a security advisory recommends a later release, Cisco recommends following the advisory guidance.

  Cisco ASA Compatibility
  Cisco Secure Firewall ASA Upgrade Guide
  Cisco Secure Firewall Threat Defense Compatibility Guide

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-asa-webvpn-dos-3GhZQBAS

Revision History

• Version	Description	Section	Status	Date
  1.1	Updated the Cisco Software Checker form.	Fixed Software	Final	2023-NOV-02
  1.0	Initial public release.	—	Final	2023-NOV-01

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