CVE-2026-20024 is a vulnerability identified in the Open Shortest Path First (OSPF) protocol implementation within Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firepower Threat Defense (FTD) Software. The flaw arises from improper restriction of operations within the bounds of a memory buffer, specifically a heap corruption issue triggered when parsing OSPF packets. An attacker who is authenticated and adjacent on the network, and who possesses the OSPF secret key, can send specially crafted OSPF packets to the vulnerable device. This crafted input corrupts the heap memory, leading to an unexpected reload of the device, effectively causing a denial-of-service (DoS) condition. The vulnerability affects a wide range of Cisco ASA and FTD software versions, spanning multiple releases from 9.12.1 through 9.23.1. The CVSS v3.1 base score is 6.8, reflecting medium severity, with attack vector being adjacent network, low attack complexity, requiring privileges (OSPF secret key), no user interaction, and scope changed due to impact on device availability. The vulnerability does not impact confidentiality or integrity but significantly affects availability. No public exploits have been reported yet, but the requirement for OSPF secret key and adjacency limits the attack surface. The flaw underscores the criticality of secure OSPF configurations and patch management in network perimeter devices.

The primary impact of CVE-2026-20024 is a denial-of-service condition on Cisco Secure Firewall ASA and FTD devices, which are widely used in enterprise and service provider networks for perimeter security and routing. A successful exploit causes device reloads, resulting in temporary loss of firewall and routing functionality. This can disrupt network traffic, degrade security posture, and potentially cause outages in critical infrastructure, enterprise networks, and data centers. Since the vulnerability requires adjacency and possession of the OSPF secret key, the risk is mitigated somewhat but remains significant in environments where OSPF neighbors are not fully trusted or where key management is weak. The DoS can impact availability of protected resources, leading to operational downtime, loss of business continuity, and increased risk of secondary attacks during recovery windows. Organizations relying heavily on Cisco ASA/FTD for secure routing and firewalling, especially those with complex OSPF topologies, are at risk of network instability and security gaps if unpatched.

1. Apply Cisco's official patches and software updates for all affected ASA and FTD versions as soon as they become available to remediate the heap corruption vulnerability. 2. Restrict OSPF adjacency to trusted and authenticated devices only; enforce strict OSPF authentication using strong, regularly rotated secret keys to prevent unauthorized adjacency. 3. Implement network segmentation and access controls to limit which devices can establish OSPF adjacency with critical firewall devices, reducing exposure to adjacent attackers. 4. Monitor OSPF traffic for anomalous or malformed packets that could indicate exploitation attempts. 5. Employ redundancy and high availability configurations to minimize impact of device reloads caused by potential exploitation. 6. Conduct regular audits of OSPF configurations and secret key management to ensure compliance with security best practices. 7. Use intrusion detection/prevention systems (IDS/IPS) capable of detecting suspicious OSPF packet patterns. 8. Maintain comprehensive incident response plans to quickly address any DoS incidents affecting firewall devices.