CVE-2023-20042: Cisco Security Advisory: Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software AnyConnect SSL/TLS VPN Denial of Service Vulnerability

Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software AnyConnect SSL/TLS VPN Denial of Service Vulnerability

Medium

CVE-2023-20042

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Summary

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• A vulnerability in the AnyConnect SSL 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 an implementation error within the SSL/TLS session handling process that can prevent the release of a session handler under specific conditions. An attacker could exploit this vulnerability by sending crafted SSL/TLS traffic to an affected device, increasing the probability of session handler leaks. A successful exploit could allow the attacker to eventually deplete the available session handler pool, preventing new sessions from being established and causing 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-asaftd-ssl-dos-kxG8mpUA

  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.

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Affected Products

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• At the time of publication, this vulnerability affected Cisco ASA Software and FTD Software that was configured for AnyConnect SSL/TLS VPN connections.

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

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

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Indicators of Compromise

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• It is possible to detect the presence of leaked session handlers using the command show SSL objects. An abnormal and increasing number in the SSL: active counter indicates that sessions are leaking.

  ASA/FTD# show SSL objects
  SSL object statistics:
  SSL: active: 29778, peak: 29793, total: 2507224
  SSL_CTX: active: 4, peak: 6, total: 1704772
  SSL_SESSION: active: 30548, peak: 30796, total: 1076386
  X509: active: 15, peak: 16, total: 3036
  X509_STORE: active: 6, peak: 9, total: 1704819
  X509_STORE_CTX: active: 0, peak: 3, total: 796310
  DH: active: 2, peak: 8, total: 2035
  EC_KEY: active: 12, peak: 14, total: 480347
  RSA: active: 16, peak: 18, total: 1529
  ENGINE: active: 2, peak: 2, total: 2
  BIO: active: 52367, peak: 52385, total: 5642732
  DRBG: active: 18446744073709541998, peak: 0, total: 0
  103132 active objects, 13919192 total objects

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Workarounds

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• There are no workarounds that address this vulnerability.

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Fixed Software

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• 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.

  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.

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

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Exploitation and Public Announcements

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• The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.

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Source

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• This vulnerability was found during the resolution of a Cisco TAC support case.

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Cisco Security Vulnerability Policy

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• To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.

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Related to This Advisory

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• Cisco Event Response: November 2023 Cisco ASA, FMC, and FTD Software Security Advisory Bundled Publication

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URL

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• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-ssl-dos-kxG8mpUA

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Revision History

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• Version

  Description

  Section

  Status

  Date

  1.0

  Initial public release.

  -

  Final

  2023-NOV-01

  Show Less

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Legal Disclaimer

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• THIS DOCUMENT IS PROVIDED ON AN “AS IS” BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.

  A standalone copy or paraphrase of the text of this document that omits the distribution URL is an uncontrolled copy and may lack important information or contain factual errors. The information in this document is intended for end users of Cisco products.

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