Cisco Secure Firewall Adaptive Security Appliance Software Remote Access SSL VPN allocation of resources

Summaryinfo

A vulnerability marked as critical has been reported in Cisco Secure Firewall Adaptive Security Appliance Software and Secure Firewall Threat Defense Software. This affects an unknown part of the component Remote Access SSL VPN. The manipulation leads to allocation of resources. This vulnerability is traded as CVE-2026-20103. It is possible to initiate the attack remotely. There is no exploit available. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as critical, has been found in Cisco Secure Firewall Adaptive Security Appliance Software and Secure Firewall Threat Defense Software (the affected version is unknown). This issue affects an unknown code of the component Remote Access SSL VPN. The manipulation with an unknown input leads to a allocation of resources vulnerability. Using CWE to declare the problem leads to CWE-770. The product allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor. Impacted is availability. The summary by CVE is:

A vulnerability in the Remote Access SSL VPN functionality of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to exhaust device memory resulting in a denial of service (DoS) condition to new Remote Access SSL VPN connections. This does not affect the management interface, though it may become temporarily unresponsive. This vulnerability is due to trusting user input without validation. 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 web interface to stop responding, resulting in a DoS condition.

It is possible to read the advisory at sec.cloudapps.cisco.com. The identification of this vulnerability is CVE-2026-20103 since 10/08/2025. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 05/02/2026). The attack technique deployed by this issue is T1499 according to MITRE ATT&CK.

The vulnerability scanner Nessus provides a plugin with the ID 311458 (Cisco Firepower Threat Defense (FTD) Software VPN DoS Vulnerabilities (cisco-sa-asaftd-vpn-m9sx6MbC)), which helps to determine the existence of the flaw in a target environment.

Upgrading eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at Tenable (311458). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

Type

• Firewall Software

Vendor

• Cisco

Name

• Secure Firewall Adaptive Security Appliance Software
• Secure Firewall Threat Defense Software

License

• commercial

Website

• Vendor: https://www.cisco.com/

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Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

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