CVE-2026-20105 is a vulnerability identified in the Remote Access SSL VPN functionality of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Secure Firewall Threat Defense (FTD) Software. The root cause is a failure to properly release allocated memory after its effective lifetime due to trusting user input without sufficient validation. An authenticated attacker with a valid VPN connection can send specially crafted packets to the SSL VPN server, triggering memory exhaustion on the device. This memory leak leads to resource depletion, causing the device to reload and resulting in a denial of service (DoS) condition. The vulnerability affects numerous versions of Cisco ASA software, spanning from 9.12.1 through 9.23.1.3, covering many minor and patch releases, indicating a widespread exposure. The management and MUS interfaces are not affected, limiting the attack vector to VPN users only. The CVSS v3.1 base score is 7.7 (high severity), reflecting the network attack vector, low attack complexity, required privileges (authenticated VPN user), no user interaction, and a scope change due to device reload impacting availability. Although no known exploits have been reported in the wild, the vulnerability poses a significant risk to organizations relying on Cisco ASA/FTD devices for secure remote access. The vulnerability's exploitation can disrupt critical network security infrastructure, potentially impacting business continuity and security monitoring capabilities.

The primary impact of CVE-2026-20105 is a denial of service (DoS) condition caused by memory exhaustion leading to device reloads. Organizations using Cisco Secure Firewall ASA or FTD devices for remote access VPN services may experience service outages, disrupting remote connectivity for employees and partners. This can lead to operational downtime, reduced productivity, and potential loss of access to critical internal resources. The DoS condition could also degrade the overall security posture by temporarily disabling firewall protections and VPN access controls, potentially exposing the network to further attacks during downtime. Since the vulnerability requires authenticated VPN access, the risk is somewhat mitigated by the need for valid credentials; however, insider threats or compromised VPN accounts could be leveraged by attackers. The widespread use of Cisco ASA/FTD devices globally, especially in enterprises, government agencies, and critical infrastructure sectors, amplifies the potential impact. Persistent or repeated exploitation could cause repeated disruptions, complicating incident response and recovery efforts.

1. Immediate application of Cisco's security patches or updates addressing CVE-2026-20105 is the most effective mitigation. Organizations should prioritize upgrading affected ASA/FTD software versions to fixed releases once available. 2. Restrict VPN access to trusted users and enforce strong authentication mechanisms such as multi-factor authentication (MFA) to reduce the risk of credential compromise. 3. Monitor VPN server logs and network traffic for unusual patterns or spikes in SSL VPN connections that could indicate exploitation attempts. 4. Implement rate limiting or connection throttling on the SSL VPN interface to mitigate potential memory exhaustion from crafted packets. 5. Regularly audit and review VPN user accounts to disable inactive or unnecessary accounts, minimizing the attack surface. 6. Employ network segmentation to isolate VPN infrastructure from critical internal systems, limiting the blast radius of any DoS event. 7. Prepare incident response plans specifically for VPN service disruptions, including fallback remote access methods. 8. Engage with Cisco support and subscribe to security advisories to stay informed about patches and mitigation guidance. 9. Consider deploying additional monitoring tools that can detect memory leaks or abnormal resource usage on ASA/FTD devices. 10. If immediate patching is not feasible, temporarily disable or limit Remote Access SSL VPN functionality where possible until remediation is applied.