CVE-2026-20105 in Secure Firewall Adaptive Security Appliance Software
Summary
by MITRE • 03/04/2026
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. 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 reload, resulting in a DoS condition.
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Analysis
by VulDB Data Team • 03/04/2026
The vulnerability identified as CVE-2026-20105 represents a critical memory exhaustion flaw within Cisco's Secure Firewall Adaptive Security Appliance and Secure Firewall Threat Defense software implementations. This weakness specifically targets the Remote Access SSL VPN functionality, creating a pathway for authenticated remote attackers to manipulate device resources through carefully crafted network packets. The vulnerability manifests when the system processes user input without proper validation mechanisms, allowing maliciously constructed data to consume system memory resources beyond normal operational limits. This design flaw directly violates fundamental security principles that require input sanitization and validation before processing potentially untrusted data streams.
The technical exploitation of this vulnerability occurs through the Remote Access SSL VPN server component, where an authenticated attacker with a valid VPN connection can send specifically crafted packets designed to trigger memory allocation patterns that gradually consume available system resources. This process leads to a gradual depletion of memory capacity until the device reaches a critical threshold where it can no longer maintain normal operations. The DoS condition ultimately results in device reloads, effectively disrupting network connectivity for legitimate users while potentially creating service interruptions that can impact business operations and network availability. The vulnerability's impact is particularly concerning because it leverages existing authenticated access, meaning attackers who have already established a VPN session can escalate their privileges through resource exhaustion rather than attempting to bypass authentication mechanisms.
From a security operations perspective, this vulnerability creates significant risk for organizations relying on Cisco ASA and FTD platforms for network security. The fact that it does not affect management or MUS interfaces provides some limited protection, but the core VPN functionality remains compromised, potentially allowing attackers to maintain persistent access while simultaneously degrading service availability. The vulnerability aligns with CWE-20, which describes improper input validation as a fundamental weakness in software design, and maps to ATT&CK technique T1499.004 for network denial of service attacks. Organizations utilizing these platforms face potential operational impacts including extended service interruptions, increased administrative overhead for system recovery, and potential business disruption during attack windows.
Mitigation strategies for CVE-2026-20105 should prioritize immediate implementation of software patches provided by Cisco to address the input validation gap in the VPN processing components. Network administrators should consider implementing additional monitoring controls to detect unusual memory consumption patterns and establish automated alerting for potential exploitation attempts. Access control measures should be reinforced to limit the number of concurrent VPN sessions and implement rate limiting for packet processing to prevent rapid resource exhaustion. Organizations should also maintain detailed incident response procedures specifically addressing DoS conditions related to VPN services, including protocols for rapid system recovery and potential network isolation measures during active exploitation attempts. The vulnerability demonstrates the importance of implementing defense-in-depth strategies where multiple layers of security controls work together to prevent single points of failure in critical network infrastructure components.