CVE-2026-20015 is a vulnerability identified in the Internet Key Exchange version 2 (IKEv2) implementation of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firepower Threat Defense (FTD) Software. The flaw arises from a memory leak during the parsing of IKEv2 packets, where memory allocated for processing is not properly released after its effective lifetime. An unauthenticated remote attacker can exploit this by sending specially crafted IKEv2 packets to the affected device, causing it to consume excessive memory resources. Over time, this resource exhaustion leads to a denial-of-service (DoS) condition, impairing the firewall's ability to process legitimate traffic and potentially disrupting network services for connected devices. The DoS condition necessitates manual intervention to reload the device and restore normal operation. The vulnerability affects a broad range of software versions from 9.18.1 through 9.23.1, indicating a widespread exposure across many Cisco ASA and FTD deployments. The CVSS v3.1 base score is 5.8, reflecting medium severity due to the lack of impact on confidentiality or integrity, but significant impact on availability. The attack vector is network-based with low complexity, requiring no privileges or user interaction, which increases the risk of exploitation. However, no known exploits have been reported in the wild as of the publication date. This vulnerability highlights the importance of robust memory management in protocol implementations and the critical role of firewall availability in network security.

The primary impact of CVE-2026-20015 is a denial-of-service condition on Cisco Secure Firewall ASA and FTD devices, which are widely deployed as perimeter security solutions in enterprise and service provider networks globally. Successful exploitation can exhaust memory resources, causing the firewall to become unresponsive and disrupt traffic filtering and VPN termination services. This can lead to network outages, loss of connectivity, and potential exposure to other threats due to the absence of firewall protections during downtime. Organizations relying on these devices for secure remote access via IKEv2 VPNs may experience significant operational disruptions. The requirement for manual device reload increases downtime and operational costs. While confidentiality and integrity are not directly impacted, the availability degradation can have cascading effects on business continuity, incident response capabilities, and compliance with security policies. The vulnerability's ease of exploitation without authentication and user interaction further elevates the risk, especially in environments exposed to untrusted networks.

To mitigate CVE-2026-20015, organizations should prioritize upgrading affected Cisco ASA and FTD devices to the latest patched software versions provided by Cisco once available. In the interim, network administrators can implement the following specific measures: 1) Restrict access to the IKEv2 service by limiting inbound UDP ports 500 and 4500 to trusted IP addresses only, reducing exposure to unauthenticated attackers. 2) Deploy intrusion prevention system (IPS) signatures or firewall rules to detect and block anomalous or malformed IKEv2 packets that may trigger the memory leak. 3) Monitor firewall resource utilization closely for unusual memory consumption patterns indicative of exploitation attempts. 4) Employ rate limiting on IKEv2 traffic to prevent resource exhaustion from high volumes of crafted packets. 5) Maintain rigorous network segmentation to isolate critical firewall infrastructure from untrusted networks. 6) Prepare incident response procedures for rapid device reload and recovery in case of DoS events. These targeted mitigations complement patching efforts and help reduce the attack surface while maintaining firewall availability.