CVE-2026-20103 Cisco CVE debrief

Who should care

Organizations using Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Secure Firewall Threat Defense (FTD) Software should be aware of this vulnerability and take steps to mitigate it. This includes prioritizing patching to prevent potential denial of service (DoS) attacks, implementing compensating controls such as monitoring and filtering traffic to the Remote Access SSL VPN server, and conducting regular security audits and vulnerability assessments to identify potential weaknesses. Security teams and vulnerability management teams should review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance, and plan vendor-supported updates or mitigations through normal change control where exposure is confirmed. IT operators and administrators of affected systems should also review compensating controls for exposed systems while remediation is scheduled and verified, and check relevant monitoring, detection, and logs for exposed assets that need extra review. Asset inventory and change management processes should be updated to reflect the vulnerability and associated risks. This vulnerability may impact the security posture of organizations relying on these products for remote access, and therefore requires prompt attention and mitigation to minimize potential operational impact and security risks. Security teams should track exceptions, retest remediated assets, and close the item only after evidence is documented. The vulnerability management process should be updated to include this vulnerability and associated risks, and to ensure that affected systems are properly patched or mitigated. The security posture of organizations using these products may be impacted if the vulnerability is not properly addressed, and therefore requires prompt attention and mitigation to minimize potential operational impact and security risks. The vulnerability management process should be updated to include this vulnerability and associated risks, and to ensure that affected systems are properly patched or mitigated. The security posture of organizations using these products may be impacted if the vulnerability is n

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 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. 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 web interface to stop responding, resulting in a DoS condition. The vulnerability affects Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Secure Firewall Threat Defense (FTD) Software.

Defensive priority

Organizations using Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Secure Firewall Threat Defense (FTD) Software should prioritize patching to prevent potential denial of service (DoS) attacks.

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.
• Implement compensating controls such as monitoring and filtering traffic to the Remote Access SSL VPN server.
• Conduct regular security audits and vulnerability assessments to identify potential weaknesses.
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.
• Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance.
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed.
• Check relevant monitoring, detection, and logs for exposed assets that need extra review.

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.

Official resources