Cisco Secure Firewall Adaptive Security Appliance and Secure Firewall Threat Defense Software Remote Access SSL VPN Denial of Service Vulnerability

A vulnerability in the Remote Access SSL VPN service for Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the device to reload unexpectedly, resulting in a denial of service (DoS) condition. This vulnerability is due to insufficient error checking when processing HTTP requests. An attacker could exploit this vulnerability by sending a crafted HTTP request to the Remote Access SSL VPN service on an affected device. A successful exploit could allow the attacker to cause the affected device to reload, 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: This advisory is part of a group of advisories. For a complete list of the advisories and links to them, see Cisco Advance Notification for Publication of September 16, 2026, Security Advisories . In addition, for further documentation of improvements and fixes in Cisco Secure Firewall products, see Cisco Secure Firewall Adaptive Security Appliance Software, Secure Firewall Threat Defense Software, and Secure Firewall Management Center Software Hardening Release: September 2026 .

A vulnerability in the Remote Access SSL VPN service for Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the device to reload unexpectedly, resulting in a denial of service (DoS) condition.

This vulnerability is due to insufficient error checking when processing HTTP requests. An attacker could exploit this vulnerability by sending a crafted HTTP request to the Remote Access SSL VPN service on an affected device. A successful exploit could allow the attacker to cause the affected device to reload, 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:

This advisory is part of a group of advisories. For a complete list of the advisories and links to them, see Cisco Advance Notification for Publication of September 16, 2026, Security Advisories . In addition, for further documentation of improvements and fixes in Cisco Secure Firewall products, see Cisco Secure Firewall Adaptive Security Appliance Software, Secure Firewall Threat Defense Software, and Secure Firewall Management Center Software Hardening Release: September 2026 .

Vulnerable Products This vulnerability affects Cisco devices if they are running a vulnerable release of Cisco Secure Firewall ASA Software or Cisco Secure FTD Software and have one or more of the vulnerable configurations listed in the following table. For information which Cisco software releases are vulnerable, see the Fixed Software section of this advisory. Cisco Secure Firewall ASA and FTD Software Vulnerable Configurations In the following table, the left column lists Cisco Secure Firewall ASA and Secure FTD Software features that are potentially vulnerable. The right column indicates the basic configuration for the feature from the show running-config CLI command. These features could enable the SSL listen sockets. Cisco Secure Firewall ASA and FTD Software Feature Possible Vulnerable Configuration IKEv2 Remote Access VPN (with client services) 1 crypto ikev2 enable client-services port SSL VPN 1 webvpn enable Zero Trust Network Access 2 zero-trust enable 1. For Cisco Secure FTD Software, remote access VPN features are enabled from Devices > VPN > Remote Access in Cisco Secure Firewall Management Center (FMC) Software or from Remote Access VPN in Cisco Secure Firewall Device Manager (FDM). 2. This feature is available only in Cisco Secure FTD Software. 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 Secure Firewall Management Center (FMC) Software.

This vulnerability affects Cisco devices if they are running a vulnerable release of Cisco Secure Firewall ASA Software or Cisco Secure FTD Software and have one or more of the vulnerable configurations listed in the following table.

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

Cisco Secure Firewall ASA and FTD Software Vulnerable Configurations

In the following table, the left column lists Cisco Secure Firewall ASA and Secure FTD Software features that are potentially vulnerable. The right column indicates the basic configuration for the feature from the show running-config CLI command. These features could enable the SSL listen sockets.

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 Secure Firewall Management Center (FMC) Software.

There are no workarounds that address this vulnerability.

There are no workarounds that address this vulnerability.

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. Fixed Releases In the following tables, the left column lists Cisco software releases. The right column indicates whether a release is affected by the vulnerability that is described in this advisory and the first release that includes the fix for this vulnerability. Customers are advised to upgrade to an appropriate fixed software release as indicated in this section. Cisco Secure Firewall ASA Software Release First Fixed Release 9.16 and earlier 9.16.4.103 9.18 9.18.4.94 9.20 9.20.4.49 9.22 9.22.3.26 9.23 9.23.1.47 9.24 9.24.1.26 Cisco Secure FTD Software Release and Secure FMC Software Release First Fixed Release 7.0 and earlier 7.0.10 7.2 7.2.12 7.4 7.4.8 7.6 7.6.6 7.7 7.7.13 10.0 10.0.2 10.1 10.1.0 Note: Previously, hot fixes were provided to remediate this vulnerability. At the time of this update, the hardening releases in the preceding tables have been published and include the fix for this vulnerability as well as multiple other internally discovered vulnerabilities. Cisco recommends that customers upgrade to the appropriate hardening release for their devices. If more information is needed on the previously available hot fixes, the Cisco Technical Assistance Center (TAC). The Cisco Product Security Incident Response Team (PSIRT) validates only the affected and fixed release information that is documented 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 for vulnerabilities that affect a specific software release. To use the form, follow these steps: Choose which advisories the tool will -all advisories, only advisories with a Critical or High Security Impact Rating (SIR) , or only this advisory. Choose the appropriate software. Choose the appropriate platform. 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. Click Check . 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

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.

In the following tables, the left column lists Cisco software releases. The right column indicates whether a release is affected by the vulnerability that is described in this advisory and the first release that includes the fix for this vulnerability. Customers are advised to upgrade to an appropriate fixed software release as indicated in this section.

Note: Previously, hot fixes were provided to remediate this vulnerability. At the time of this update, the hardening releases in the preceding tables have been published and include the fix for this vulnerability as well as multiple other internally discovered vulnerabilities. Cisco recommends that customers upgrade to the appropriate hardening release for their devices. If more information is needed on the previously available hot fixes, the Cisco Technical Assistance Center (TAC).

The Cisco Product Security Incident Response Team (PSIRT) validates only the affected and fixed release information that is documented 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 for vulnerabilities that affect a specific software release. To use the form, follow these steps:

Choose which advisories the tool will -all advisories, only advisories with a Critical or High Security Impact Rating (SIR) , or only this advisory.

Choose the appropriate software.

Choose the appropriate platform.

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.

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

In August 2026, the Cisco PSIRT became aware of active exploitation of this vulnerability. Cisco strongly recommends that customers upgrade to a fixed software release to remediate this vulnerability.

In August 2026, the Cisco PSIRT became aware of active exploitation of this vulnerability. Cisco strongly recommends that customers upgrade to a fixed software release to remediate this vulnerability.

This vulnerability was found during internal security testing. It was also reported to Cisco by Valerio Brussani - @val_brux (harmonyguard.cloud).

This vulnerability was found during internal security testing. It was also reported to Cisco by Valerio Brussani - @val_brux (harmonyguard.cloud).

Cisco Security Vulnerability Policy

To learn 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. For additional information on Cisco's vulnerability management, disclosure cadence, and software patching strategy, see Cisco's Transition to a Risk-Based Vulnerability Disclosure Model .

To learn 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.

For additional information on Cisco's vulnerability management, disclosure cadence, and software patching strategy, see Cisco's Transition to a Risk-Based Vulnerability Disclosure Model .

Action Links for This Advisory

Snort Rule 46897 Snort Rule 59654

Related to This Advisory

Version Description Section Status Date 1.1 Updated fixed release information and added reference to security hardening releases. Summary and Fixed Releases Final 2026-SEP-16 1.0 Initial public release. - Final 2026-AUG-11 Show Less

SOFTWARE DOWNLOADS AND TECHNICAL SUPPORT The Cisco Support and Downloads page on Cisco.com provides information licensing and downloads. This page can also display customer device support coverage for customers who use the My Devices tool. Please note that customers may download only software that was procured from Cisco directly or through a Cisco authorized reseller or partner and for which the license is still valid. 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 Technical Assistance Center (TAC) . 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. When considering software upgrades , customers are advised to regularly consult the advisories for the relevant Cisco products 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 the Cisco Technical Assistance Center (TAC) or their contracted maintenance providers. LEGAL DISCLAIMER DETAILS CISCO DOES NOT MAKE ANY EXPRESS OR IMPLIED GUARANTEES OR WARRANTIES OF ANY KIND, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. WITHOUT LIMITING THE GENERALITY OF THE FOREGOING, CISCO DOES NOT GUARANTEE THE ACCURACY OR COMPLETENESS OF THIS INFORMATION. THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS. 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. Copies or summaries of the information contained in this Security Advisory may lack important information or contain factual errors. Customers are advised to visit the Cisco Security Advisories page for the most recent version of this Security Advisory. The Cisco Product Security Incident Response Team (PSIRT) assesses only the affected and fixed release information that is documented in this advisory. See the Cisco Security Vulnerability Policy for more information.

SOFTWARE DOWNLOADS AND TECHNICAL SUPPORT

The Cisco Support and Downloads page on Cisco.com provides information licensing and downloads. This page can also display customer device support coverage for customers who use the My Devices tool. Please note that customers may download only software that was procured from Cisco directly or through a Cisco authorized reseller or partner and for which the license is still valid.

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 Technical Assistance Center (TAC) . 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.

When considering software upgrades , customers are advised to regularly consult the advisories for the relevant Cisco products 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 the Cisco Technical Assistance Center (TAC) or their contracted maintenance providers.

LEGAL DISCLAIMER DETAILS

CISCO DOES NOT MAKE ANY EXPRESS OR IMPLIED GUARANTEES OR WARRANTIES OF ANY KIND, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. WITHOUT LIMITING THE GENERALITY OF THE FOREGOING, CISCO DOES NOT GUARANTEE THE ACCURACY OR COMPLETENESS OF THIS INFORMATION. THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS. 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.

Copies or summaries of the information contained in this Security Advisory may lack important information or contain factual errors. Customers are advised to visit the Cisco Security Advisories page for the most recent version of this Security Advisory. The Cisco Product Security Incident Response Team (PSIRT) assesses only the affected and fixed release information that is documented in this advisory. See the Cisco Security Vulnerability Policy for more information.

Leave additional feedback