Cisco Security Advisory
Cisco Secure Firewall Adaptive Security Appliance and Secure Firewall Threat Defense Software Remote Access SSL VPN Denial of Service Vulnerability
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CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X
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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:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-vpn-dos-dzv4mQFF
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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 about 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 <interface_name> client-services port <port_numbers>
SSL VPN1 webvpn
enable <interface_name>Zero Trust Network Access2 zero-trust
enable1. 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.
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There are no workarounds that address this vulnerability.
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Cisco considers any workarounds and mitigations (if applicable) to be temporary solutions until an upgrade to a fixed software release is available. To fully 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 Hot Fixes
Cisco has released the following hot fixes to address this vulnerability. Customers can download the hot fixes from the Software Center on Cisco.com.
Cisco Secure Firewall ASA Software Release Hot Fix Name 9.161 89.16.4.50 9.181 89.18.4.50 9.20 9.20.4.235 9.22 9.22.3.191 9.23 9.23.1.211 9.24 9.24.1.221 1. When installing a hot fix that starts with 89, install ASDM Release 7.24.1.374 because previous releases of ASDM do not recognize this ASA Software release numbering format.Cisco Secure FTD Hot Fixes
Cisco Secure FTD Software Release Hot Fix Name 7.0 Cisco_FTD_Hotfix_GC-7.0.9.1-1.sh.REL.tar
Cisco_FTD_SSP_FP1K_Hotfix_GC-7.0.9.1-1.sh.REL.tar
Cisco_FTD_SSP_FP2K_Hotfix_GC-7.0.9.1-1.sh.REL.tar
Cisco_FTD_SSP_Hotfix_GC-7.0.9.1-1.sh.REL.tar7.2 Cisco_FTD_Hotfix_HM-7.2.11.1-2.sh.REL.tar
Cisco_FTD_SSP_FP1K_Hotfix_HM-7.2.11.1-2.sh.REL.tar
Cisco_FTD_SSP_FP2K_Hotfix_HM-7.2.11.1-2.sh.REL.tar
Cisco_FTD_SSP_FP3K_Hotfix_HM-7.2.11.1-2.sh.REL.tar
Cisco_FTD_SSP_Hotfix_HM-7.2.11.1-2.sh.REL.tar7.4 Cisco_FTD_Hotfix_HK-7.4.7.1-1.sh.REL.tar
Cisco_FTD_SSP_FP1K_Hotfix_HK-7.4.7.1-1.sh.REL.tar
Cisco_FTD_SSP_FP2K_Hotfix_HK-7.4.7.1-1.sh.REL.tar
Cisco_FTD_SSP_FP3K_Hotfix_HK-7.4.7.1-1.sh.REL.tar
Cisco_FTD_SSP_Hotfix_HK-7.4.7.1-1.sh.REL.tar
Cisco_Secure_FW_TD_4200_Hotfix_HK-7.4.7.1-1.sh.REL.tar7.6 Cisco_FTD_Hotfix_DD-7.6.4.1-2.sh.REL.tar
Cisco_FTD_SSP_FP1K_Hotfix_DD-7.6.4.1-2.sh.REL.tar
Cisco_FTD_SSP_FP3K_Hotfix_DD-7.6.4.1-2.sh.REL.tar
Cisco_FTD_SSP_Hotfix_DD-7.6.4.1-2.sh.REL.tar
Cisco_Secure_FW_TD_4200_Hotfix_DD-7.6.4.1-2.sh.REL.tar7.7 Cisco_FTD_Hotfix_AN-7.7.11.1-2.sh.REL.tar
Cisco_FTD_SSP_FP1K_Hotfix_AN-7.7.11.1-2.sh.REL.tar
Cisco_FTD_SSP_FP3K_Hotfix_AN-7.7.11.1-2.sh.REL.tar
Cisco_FTD_SSP_Hotfix_AN-7.7.11.1-2.sh.REL.tar
Cisco_Secure_FW_TD_1200_Hotfix_AN-7.7.11.1-2.sh.REL.tar
Cisco_Secure_FW_TD_4200_Hotfix_AN-7.7.11.1-2.sh.REL.tar10.0 Cisco_FTD_Hotfix_S-10.0.0.1-2.sh.REL.tar
Cisco_FTD_SSP_FP1K_Hotfix_S-10.0.0.1-2.sh.REL.tar
Cisco_FTD_SSP_FP3K_Hotfix_S-10.0.0.1-2.sh.REL.tar
Cisco_FTD_SSP_Hotfix_S-10.0.0.1-2.sh.REL.tar
Cisco_Secure_FW_TD_200_Hotfix_R-10.0.0.1-2.sh.REL.tar
Cisco_Secure_FW_TD_1200_Hotfix_S-10.0.0.1-2.sh.REL.tar
Cisco_Secure_FW_TD_4200_Hotfix_S-10.0.0.1-2.sh.REL.tar
Cisco_Secure_FW_TD_6100_Hotfix_S-10.0.0.1-2.sh.REL.tarNote: For instructions on upgrading a Cisco Secure FTD device, see the appropriate Cisco Secure FMC upgrade guide.
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:
- Choose which advisories the tool will search-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
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In August 2026, the Cisco Product Security Incident Response Team (PSIRT) became aware of active exploitation of this vulnerability. Cisco strongly recommends that customers upgrade to a fixed software release to remediate this vulnerability.
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This vulnerability was found during internal security testing. It was also reported to Cisco by Valerio Brussani - @val_brux (harmonyguard.cloud).
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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.
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.
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Show LessVersion Description Section Status Date 1.0 Initial public release. - Final 2026-AUG-11
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SOFTWARE DOWNLOADS AND TECHNICAL SUPPORT
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. 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 contact 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.