CVE-2026-20106 in Secure Firewall Adaptive Security Appliance Software
Summary
by MITRE • 03/04/2026
A vulnerability in the Remote Access SSL VPN, HTTP management and MUS 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 requiring a manual reboot. 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 to stop responding, resulting in a DoS condition.
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Analysis
by VulDB Data Team • 03/04/2026
The vulnerability identified as CVE-2026-20106 represents a critical memory exhaustion flaw within Cisco's Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) software implementations. This weakness specifically targets the Remote Access SSL VPN, HTTP management, and MUS functionality components, creating a pathway for unauthenticated remote attackers to deliberately consume system resources. The vulnerability stems from insufficient input validation mechanisms that fail to properly sanitize or verify incoming data packets, allowing malicious payloads to bypass normal security checks and exploit the device's memory management systems.
The technical exploitation of this vulnerability occurs through carefully crafted network packets sent to the Remote Access SSL VPN server component of affected devices. When the system receives these malformed inputs, it processes them without adequate validation, leading to progressive memory consumption that eventually exhausts available system resources. This memory exhaustion results in the device becoming unresponsive and unable to process legitimate network traffic, effectively creating a denial of service condition that requires manual intervention through device rebooting. The flaw operates at the protocol level where user-supplied data is blindly trusted and processed, creating a direct path to system instability.
From an operational impact perspective, this vulnerability presents a significant risk to network availability and business continuity for organizations relying on Cisco ASA and FTD appliances for their security infrastructure. The remote nature of the exploit means that attackers can target vulnerable devices from anywhere on the internet without requiring authentication credentials or physical access. The resulting DoS condition disrupts network services and can potentially affect critical business operations, especially in environments where these appliances serve as primary security gateways. The need for manual reboot operations creates additional downtime and operational overhead for security teams.
The vulnerability aligns with CWE-20, "Improper Input Validation," which classifies this issue as a fundamental security flaw where input data is not properly validated before processing. This weakness allows attackers to manipulate system behavior through crafted inputs, leading to resource exhaustion and system instability. From an ATT&CK framework perspective, this vulnerability maps to T1499.004, "Endpoint Denial of Service," where adversaries leverage system weaknesses to consume resources and render systems unavailable. The threat actor profile indicates this vulnerability could be exploited by automated scanning tools that identify vulnerable targets and systematically attempt memory exhaustion attacks.
Organizations should implement immediate mitigations including applying the latest security patches released by Cisco, implementing network segmentation to limit exposure of vulnerable appliances, and deploying intrusion detection systems to monitor for suspicious packet patterns. Network administrators should also consider disabling unnecessary services and implementing rate limiting controls on VPN and management interfaces. The remediation process should include comprehensive testing of patches in controlled environments before deployment to production systems. Additionally, organizations should conduct vulnerability assessments to identify all affected devices and establish monitoring procedures to detect potential exploitation attempts. Regular security audits and network traffic analysis should be implemented to identify anomalous behavior that may indicate exploitation attempts.