CVE-2026-20026 is a vulnerability in Cisco Secure Firewall Threat Defense (FTD) software affecting multiple versions from 7.0.0 up to 7.4.3 and later. The flaw arises from improper buffer handling in the Snort 3 Detection Engine when processing Distributed Computing Environment / Remote Procedure Call (DCE/RPC) requests. Specifically, a double free or use-after-free condition occurs due to erroneous buffer management logic, which can be triggered by sending a large number of crafted DCE/RPC requests through an established connection inspected by Snort 3. This leads to memory corruption that causes the Snort 3 engine to crash and restart unexpectedly. The consequence is a denial of service (DoS) condition, temporarily disabling packet inspection capabilities of the firewall. The vulnerability is exploitable remotely by unauthenticated attackers without requiring user interaction, increasing its risk profile. However, it does not allow for code execution, data leakage, or privilege escalation, limiting its impact to availability. The vulnerability has a CVSS v3.1 base score of 5.8 (medium severity), reflecting its network attack vector, low complexity, no privileges required, no user interaction, and impact limited to availability. No known public exploits or active exploitation have been reported as of the publication date. The vulnerability affects a broad range of Cisco FTD versions, indicating that many deployments could be vulnerable if not updated. Cisco is expected to release patches or mitigations to address this issue. Until then, organizations should monitor network traffic for anomalous DCE/RPC request patterns and consider restricting or filtering such traffic where feasible to reduce exposure.

For European organizations, this vulnerability poses a risk of denial of service on Cisco Secure Firewall Threat Defense devices, which are widely used in enterprise and service provider networks for perimeter security and traffic inspection. An attacker exploiting this flaw can disrupt firewall operations by causing the Snort 3 Detection Engine to restart, leading to temporary loss of packet inspection and potential exposure to other threats during downtime. This can impact network availability and security monitoring capabilities, potentially affecting critical business operations and compliance with regulatory requirements such as GDPR. Organizations in sectors with high reliance on continuous network security—such as finance, healthcare, telecommunications, and government—may experience operational disruptions or increased risk exposure. The lack of confidentiality or integrity impact reduces the risk of data breaches directly from this vulnerability, but the availability impact alone can have significant operational consequences. Additionally, the ease of remote exploitation without authentication increases the likelihood of opportunistic attacks, especially in environments where DCE/RPC traffic is permitted or exposed. European entities using Cisco FTD in their security infrastructure should prioritize mitigation to maintain network resilience and compliance.

1. Apply official Cisco patches or updates as soon as they become available to remediate the vulnerability in affected FTD versions. 2. Implement network segmentation and strict access controls to limit exposure of Cisco FTD management and inspection interfaces to untrusted networks, especially restricting DCE/RPC traffic. 3. Use firewall rules or intrusion prevention system (IPS) signatures to detect and block anomalous or excessive DCE/RPC request patterns that could indicate exploitation attempts. 4. Monitor firewall and Snort 3 engine logs for unexpected restarts or crashes that may signal exploitation activity. 5. Employ rate limiting on DCE/RPC traffic where possible to reduce the risk of triggering the vulnerability through high-volume request floods. 6. Conduct regular security assessments and penetration tests to verify that mitigations are effective and that no unauthorized access paths exist to the affected systems. 7. Maintain an incident response plan that includes procedures for handling firewall outages and potential denial of service events. 8. Coordinate with Cisco support and subscribe to security advisories to stay informed about updates and emerging threats related to this vulnerability.