CVE-2026-20105 Cisco CVE debrief

Who should care

Organizations using Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Secure Firewall Threat Defense (FTD) Software with Remote Access SSL VPN functionality enabled should prioritize patching to prevent potential denial of service (DoS) conditions.

Technical summary

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 authenticated, remote attacker with a valid VPN connection to exhaust device memory resulting in a denial of service (DoS) condition. This does not affect the management or MUS interfaces. The 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 to reload, resulting in a DoS condition.

Defensive priority

Organizations using Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Secure Firewall Threat Defense (FTD) Software should prioritize patching, especially if they have Remote Access SSL VPN functionality enabled.

Recommended defensive actions

• Apply patches or updates provided by Cisco to address the vulnerability in Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Secure Firewall Threat Defense (FTD) Software.
• Restrict access to the Remote Access SSL VPN functionality to minimize exposure.
• Monitor system logs for unusual activity that could indicate exploitation attempts.
• Review compensating controls for exposed systems while remediation is scheduled and verified.
• Check relevant monitoring, detection, and logs for exposed assets that need extra review.
• Track exceptions, retest remediated assets, and close the item only after evidence is documented.
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.

Evidence notes

The vulnerability is due to trusting user input without validation in the Remote Access SSL VPN functionality of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Secure Firewall Threat Defense (FTD) Software. An attacker could exploit this vulnerability by sending crafted packets to the Remote Access SSL VPN server, potentially causing a denial of service (DoS) condition.

Official resources