Summary

• A vulnerability in the TCP Normalizer of Cisco Adaptive Security Appliance (ASA) Software and Firepower Threat Defense (FTD) Software operating in transparent mode could allow an unauthenticated, remote attacker to poison MAC address tables, resulting in a denial of service (DoS) vulnerability.

  This vulnerability is due to incorrect handling of certain TCP segments when the affected device is operating in transparent mode. An attacker could exploit this vulnerability by sending a crafted TCP segment through an affected device. A successful exploit could allow the attacker to poison the MAC address tables in adjacent devices, resulting in network disruption.

  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-ftd-dos-JxYWMJyL

  This advisory is part of the October 2021 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: October 2021 Cisco ASA, FMC, and FTD Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco products if they are running a vulnerable release of Cisco ASA Software or FTD Software and have transparent firewall mode configured.

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

  Determine the Device Configuration

  To determine whether a device is running in transparent mode, log in to the CLI and use the show firewall command. Returned values will be either Router or Transparent. The following example shows the output for a device that is in transparent mode:

  > show firewall
  Firewall mode: Transparent
  >

  For devices running in multi-context mode, use the show firewall command in every context to determine if the device is affected by this vulnerability.

  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.

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

  In the following table(s), the left column lists Cisco software releases. The center column indicates whether a release is affected by the vulnerability described in this advisory and the first release that includes the fix for this vulnerability. The right column indicates whether a release is affected by any of the Critical or High SIR vulnerabilities described in this bundle and which release includes fixes for those vulnerabilities.

  ASA Software

  Cisco ASA Software Release	First Fixed Release for This Vulnerability	First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories
  9.7 and earlier1	Migrate to a fixed release.	Migrate to a fixed release.
  9.8	9.8.4.40	9.8.4.40
  9.91	Migrate to a fixed release.	Migrate to a fixed release.
  9.101	Migrate to a fixed release.	Migrate to a fixed release.
  9.12	9.12.4.24	9.12.4.29
  9.131	Migrate to a fixed release.	Migrate to a fixed release.
  9.14	9.14.2.15	9.14.3.9
  9.15	9.15.1.15	9.15.1.17
  9.16	Not vulnerable.	9.16.2.3

  1. Cisco ASA Software releases 9.7 and earlier as well as releases 9.9, 9.10, and 9.13 have reached end of software maintenance. Customers are advised to migrate to a supported release that includes the fix for this vulnerability.

  FTD Software

  Cisco FTD Software Release	First Fixed Release for This Vulnerability	First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories
  6.2.2 and earlier1	Migrate to a fixed release.	Migrate to a fixed release.
  6.2.3	Migrate to a fixed release.	Migrate to a fixed release.
  6.3.01	Migrate to a fixed release.	Migrate to a fixed release.
  6.4.0	6.4.0.13 (Nov 2021)	6.4.0.13 (Nov 2021)
  6.5.01	Migrate to a fixed release.	Migrate to a fixed release.
  6.6.0	6.6.5	6.6.5.1
  6.7.0	6.7.0.2	6.7.0.3 (Jan 2022)
  7.0.0	Not Vulnerable.	7.0.1

  1. Cisco FMC and FTD Software releases 6.2.2 and earlier, as well as releases 6.3.0 and 6.5.0, have reached end of software maintenance. Customers are advised to migrate to a supported release that includes the fix for this vulnerability.

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

  The Cisco Product Security Incident Response Team (PSIRT) validates only the affected and fixed release information that is documented in this advisory.

Exploitation and Public Announcements

• The Cisco 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-asa-ftd-dos-JxYWMJyL

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2021-OCT-27

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