Cisco Security Advisory
Cisco Secure Firewall Adaptive Security Appliance and Secure Firewall Threat Defense Software Remote Access SSL VPN Denial of Service Vulnerabilities
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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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Multiple vulnerabilities in the Remote Access SSL VPN functionality of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow a remote attacker to cause an affected device to stop responding or to reload unexpectedly, resulting in a denial of service (DoS) condition that may require a manual reboot.
For more information about these vulnerabilities, see the Details section of this advisory.
Cisco has released software updates that address these vulnerabilities. There are no workarounds that address these vulnerabilities.
This advisory is available at the following link:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-vpn-m9sx6MbCThis advisory is part of the March 2026 release of the Cisco Secure Firewall ASA, Secure FMC, and Secure FTD Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: March 2026 Semiannual Cisco Secure Firewall ASA, Secure FMC, and Secure FTD Software Security Advisory Bundled Publication.
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Vulnerable Products
These vulnerabilities affect Cisco devices that are running a vulnerable release of Cisco Secure Firewall ASA Software or Secure FTD Software and if the Internet Key Exchange version 2 (IKEv2) Remote Access VPN with client services or Remote Access SSL VPN functionality is enabled. CVE-2026-20106 also affects the management HTTP server and Mobile User Security (MUS) features if they are enabled. For information about the vulnerable conditions for each product, see the following tables.
For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory.
Cisco Secure Firewall ASA Software Vulnerable Configurations
In the following table, the left column lists Cisco Secure Firewall ASA 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 Software Feature Possible Vulnerable Configuration IKEv2 Remote Access VPN (with client services) crypto ikev2 enable <interface name> client-services port <port_numbers>
Management Web Server Access, including Cisco Adaptive Security Device Manager (ASDM) and Cisco Security Manager access1 http server enable
httpMobile User Security (MUS) webvpn
mus password
mus server enable <port_number>
mus <IPv4_address> <IPv4_mask> <interface_name>SSL VPN webvpn
enable <interface_name>1. This feature is vulnerable only from an IP address that is in the configured access hosts.Cisco Secure FTD Software Vulnerable Configurations
In the following table, the left column lists Cisco Secure Firewall 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 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>HTTP server enabled2,3 http server enable
http1. 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. For Cisco Secure FTD Software, the HTTP feature is enabled from Devices > Platform Settings > HTTP Access in the Cisco Secure FMC Console.3. This feature is vulnerable only from an IP address that is in the configured access hosts.
Products Confirmed Not Vulnerable
Only products listed in the Vulnerable Products section of this advisory are known to be affected by these vulnerabilities.
Cisco has confirmed that these vulnerabilities do not affect Cisco Secure FMC Software.
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The vulnerabilities are not dependent on one another. Exploitation of one of the vulnerabilities is not required to exploit another vulnerability. In addition, a software release that is affected by one of the vulnerabilities may not be affected by the other vulnerabilities.
Details about the vulnerabilities are as follows:
CVE-2026-20101: Cisco Secure Firewall ASA Software and Secure FTD Software Remote Access SSL VPN Authentication DoS Vulnerability
A vulnerability in the Remote Access SSL VPN functionality of Cisco Secure Firewall ASA Software and Secure FTD Software could allow an unauthenticated, remote attacker to cause the device to reload unexpectedly, resulting in a DoS condition.
This vulnerability is due to insufficient error checking when processing VPN authentication messages. An attacker could exploit this vulnerability by sending crafted messages to the VPN authentication service. A successful exploit could allow the attacker to cause the 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.
Bug ID(s): CSCwo49932
CVE ID: CVE-2026-20101
Security Impact Rating (SIR): High
CVSS Base Score: 8.6
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:HCVE-2026-20103: Cisco Secure Firewall ASA Software and Secure FTD Software Remote Access SSL VPN Memory Exhaustion DoS Vulnerability
A vulnerability in the Remote Access SSL VPN functionality of Cisco Secure Firewall ASA Software and Secure FTD Software could allow an unauthenticated, remote attacker to exhaust device memory, resulting in a DoS to new Remote Access SSL VPN connections. This vulnerability may cause the management interface to become temporarily unresponsive.
This vulnerability is due to insufficient validation of user input. An attacker could exploit this vulnerability by sending crafted packets to the Remote Access SSL VPN server. A successful exploit could allow the attacker to cause the web interface of an affected device to stop responding, resulting in a DoS condition.
Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.
Bug ID(s): CSCwo49934
CVE ID: CVE-2026-20103
Security Impact Rating (SIR): High
CVSS Base Score: 8.6
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:HCVE-2026-20100: Cisco Secure Firewall ASA Software and Secure FTD Software Remote Access SSL VPN Lua Interpreter DoS Vulnerability
A vulnerability in the Lua interpreter of the Remote Access SSL VPN functionality of Cisco Secure Firewall ASA Software and Secure FTD Software could allow an authenticated, remote attacker with valid VPN credentials to cause the device to reload unexpectedly, resulting in a DoS condition.
This vulnerability is due to insufficient validation of user input to the Lua interpreter. An attacker could exploit this vulnerability by sending crafted HTTP packets to the Remote Access SSL VPN server. A successful exploit could allow the attacker to cause the 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.
Bug ID(s): CSCwo73889
CVE ID: CVE-2026-20100
Security Impact Rating (SIR): High
CVSS Base Score: 7.7
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:HCVE-2026-20105: Cisco Secure Firewall ASA Software and Secure FTD Software Remote Access SSL VPN Authenticated Memory Exhaustion DoS Vulnerability
A vulnerability in the Remote Access SSL VPN functionality of Cisco Secure Firewall ASA Software and Secure FTD Software could allow an authenticated, remote attacker with valid VPN credentials to exhaust device memory, resulting in a denial of service (DoS) condition.
This vulnerability is due to insufficient validation of user input. An attacker could exploit this vulnerability by sending crafted packets to the Remote Access SSL VPN server. A successful exploit could allow the attacker to cause the 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.
Bug ID(s): CSCwo73891
CVE ID: CVE-2026-20105
Security Impact Rating (SIR): High
CVSS Base Score: 7.7
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:HCVE-2026-20106: Cisco Secure Firewall ASA Software and Secure FTD Software Remote Access SSL VPN Unauthenticated Memory Exhaustion DoS Vulnerability
A vulnerability in the Remote Access SSL VPN, HTTP management, and MUS functionalities of Cisco Secure Firewall ASA Software and Secure FTD Software could allow an unauthenticated, remote attacker to exhaust device memory, resulting in a DoS condition that would require a manual reboot.
This vulnerability is due to insufficient validation of user input. An attacker could exploit this vulnerability by sending crafted packets to the Remote Access SSL VPN server. A successful exploit could allow the attacker to cause the device to stop responding, resulting in a DoS condition.
Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.
Bug ID(s): CSCwo73886
CVE ID: CVE-2026-20106
Security Impact Rating (SIR): Medium
CVSS Base Score: 5.3
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
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There are no workarounds that address these vulnerabilities.
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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 these vulnerabilities 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:
- 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.
For instructions on upgrading a Cisco Secure FTD device, see the appropriate Cisco Secure FMC upgrade guide.
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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The Cisco Product Security Incident Response Team (PSIRT) is not aware of any public announcements or malicious use of the vulnerabilities that are described in this advisory.
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CVE-2026-20100: This vulnerability was found during internal security testing by Keane O'Kelley of the Cisco Advanced Security Initiatives Group (ASIG).
CVE-2026-20101: This vulnerability was found during internal security testing by Kyle Ossinger of the Cisco ASIG.
CVE-2026-20103: This vulnerability was found during internal security testing by Alex Lumsden and Jason Crowder of the Cisco ASIG.
CVE-2026-20105 and CVE-2026-20106: These vulnerabilities were found during internal security testing by Jason Crowder of the Cisco ASIG.
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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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Show LessVersion Description Section Status Date 1.0 Initial public release. - Final 2026-MAR-04
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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.