CVE-2026-20249 in Adaptive Security Appliance Software
Summary
by MITRE • 09/16/2026
A vulnerability in the certification authentication feature of Internet Key Exchange version 2 (IKEv2) for Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause an affected device to reload unexpectedly.
This vulnerability is due to a logic error during the certificate authentication phase of the IKEv2 connection setup. An attacker could exploit this vulnerability by attempting to establish an IKEv2 VPN connection with a crafted certificate. A successful exploit could allow the attacker to cause the IKEv2 process to crash, causing a denial of service (DoS) condition.
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Analysis
by VulDB Data Team • 09/17/2026
The identified security flaw resides within the Internet Key Exchange version 2 implementation on Cisco Secure Firewall Adaptive Security Appliance and Threat Defense software platforms. This vulnerability specifically targets the certification authentication feature during the IKEv2 connection establishment phase. The core technical issue stems from a logic error that occurs when the device processes certificate-based authentication requests. Under normal operations, the firewall validates client certificates against configured trust anchors to establish secure tunnels. However, due to this specific logical defect in the processing routine, certain malformed or specially crafted certificates can trigger an internal state inconsistency within the IKEv2 daemon process. This inconsistency leads directly to a crash of the IKEv2 service, resulting in an unexpected reload of the affected firewall device.
From an operational perspective, the impact of this vulnerability is severe due to its potential for remote exploitation without prior authentication. An unauthenticated attacker located on the network can initiate a connection attempt using a crafted certificate designed to trigger the logic error. Upon successful execution of the exploit, the IKEv2 process terminates abruptly, forcing the entire firewall system to reboot. This results in a complete denial of service condition where all active VPN tunnels are dropped and traffic filtering capabilities are temporarily suspended during the reload period. The unpredictability of the crash means that network availability is compromised without warning, potentially disrupting critical business operations dependent on secure remote access or site-to-site connectivity provided by these devices.
In terms of industry standard classification, this vulnerability aligns with CWE-841 which describes Improper Enforcement of Behavioral Workflow, as the device fails to correctly enforce the expected state transitions during certificate validation. Furthermore, from a tactical standpoint within the MITRE ATT&CK framework, this exploit vector relates to T1499 Endpoint Denial of Service and potentially T1078 Valid Accounts if an attacker were able to leverage stolen credentials alongside this flaw for persistent access before triggering the crash. The lack of authentication requirement places it in the category of attacks that do not require initial foothold privileges, making it particularly dangerous against perimeter defenses.
Mitigation strategies should prioritize immediate application of vendor-provided software updates that address the logic error within the IKEv2 certificate processing module. Administrators must verify their current firmware versions and apply patches as soon as they are released by Cisco for both ASA and FTD platforms. In environments where patching is not immediately feasible, network segmentation can help isolate vulnerable devices from untrusted networks to reduce exposure to remote exploitation attempts. Additionally, implementing strict monitoring of IKEv2 connection logs may aid in detecting repeated failed authentication attempts or unusual patterns that could indicate an ongoing exploit attempt against this specific vulnerability.