Summary

• Update for September 16, 2026: The original 1.0 version of this advisory was specific to the Cisco Adaptive Security Virtual Appliance (ASAv) and Cisco Secure Firewall Threat Defense Virtual (FTDv) models. However, it was later found that this vulnerability affects all Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software platforms.

  A vulnerability in the VPN and management web servers of the Cisco Secure Firewall ASA Software and Cisco Secure FTD Software platforms could allow an unauthenticated, remote attacker to cause an affected device to run out of system memory or buffer blocks, which in turn could cause SSL VPN connection processing to slow down and eventually cease altogether.

  This vulnerability is due to a lack of proper memory management for new incoming SSL/TLS connections. An attacker could exploit this vulnerability by sending a large number of new incoming SSL/TLS connections to the targeted device. A successful exploit could allow the attacker to deplete system memory or buffers, resulting in a denial of service (DoS) condition. The memory or buffers could be reclaimed slowly if the attack traffic is stopped, but a manual reload may be required to restore operations quickly.

  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-asaftdvirtual-dos-MuenGnYR

  This advisory is part of the October 2024 release of the Cisco ASA, FMC, and FTD Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: October 2024 Semiannual 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 Secure Firewall ASA Software or Secure FTD Software and have one or both of the following features configured:

  • SSL VPN
  • HTTP server used for the management interface

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

  Determine Whether a Device Could Process SSL or TLS Messages

  To determine whether a Cisco ASA or FTD device could process SSL or TLS packets, use the show asp table socket | include SSL|DTLS command and verify that it returns output. If this command returns empty output, the device is not affected. If this command returns any output, as shown in the following example, the device is affected:

  asa# show asp table socket | include SSL|DTLS
  SSL       0005aa68  LISTEN     x.x.x.x:443      0.0.0.0:*   
  SSL       002d9e38  LISTEN     x.x.x.x:8443     0.0.0.0:*
  DTLS      0018f7a8  LISTEN     10.0.0.250:443   0.0.0.0:*  

  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 Secure Firewall Management Center (FMC) Software.

Indicators of Compromise

• A device may have been exploited by this vulnerability if the show blocks command indicates a leak of memory blocks. The device may stop passing traffic, or performance could degrade due to this memory leak. In this example, the memory blocks of 80 bytes are leaked, resulting in zero (0) blocks being available:

  # show blocks
    SIZE    MAX    LOW    CNT
       0   1450   1448   1450
       4    100     99     99
      80      1000      0      0
  
     256   4148   3898   4040
    1550   6279   6184   6258
    2048    600    598    600
    2560    164    164    164
    4096    100    100    100
    8192    100    100    100
    9344    60000  58237  59837
   16384    102    102    102
   65536     16     16     16

  For more help to determine whether the device has been impacted by exploitation of this vulnerability, contact the Cisco Technical Assistance Center (TAC).

Workarounds

• There are no workarounds that address this vulnerability.

Fixed Software

• Cisco considers any workarounds and mitigations (if applicable) to be temporary solutions until an upgrade to a fixed software release is available. To remediate this vulnerability and avoid future exposure as described in this advisory, Cisco strongly recommends that customers upgrade to the fixed software indicated in this advisory.

  Cisco Secure Firewall ASA, Secure FMC, and Secure FTD Software

  To help customers determine their exposure to vulnerabilities in Cisco Secure Firewall ASA, Secure FMC, and Secure 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, 9.20.3.4 for Cisco Secure Firewall ASA Software or 7.4.2 for Cisco Secure 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 1200 Series Secure Firewall 3100 Series Secure Firewall 4200 Series

  Note: For Cisco 3000 Series Industrial Security Appliances (ISAs) that are running Cisco Secure Firewall ASA Software, Cisco Secure Firewall ASA Software Release 9.16.4.67 has been deferred and replaced by Release 9.16.4.70.

  Additional Resources

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

  Cisco Secure Firewall 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 by Vivek Singh of Cisco during internal security testing.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftdvirtual-dos-MuenGnYR

Revision History

• Version	Description	Section	Status	Date
  2.1	Updated the products that are not vulnerable.	Products Confirmed Not Vulnerable	Final	2026-SEP-23
  2.0	Updated to indicate that this vulnerability affects all hardware platforms.	Summary, Vulnerable Products, Indicators of Compromise	Final	2026-SEP-16
  1.0	Initial public release.	-	Final	2025-AUG-27

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