CVE-2025-55669 is a vulnerability classified under CWE-672 (Operation on a Resource after Expiration or Release) affecting F5 BIG-IP versions 16.1.0 and 17.1.0. The flaw occurs when the BIG-IP Advanced Web Application Firewall (WAF) and Application Security Manager (ASM) policies are enabled in conjunction with a server-side HTTP/2 profile on a virtual server. Under these conditions, specially crafted or undisclosed traffic can cause the Traffic Management Microkernel (TMM)—the core component responsible for processing and managing network traffic—to terminate unexpectedly. This termination leads to a denial of service (DoS) condition, disrupting the availability of services managed by the BIG-IP device. The vulnerability is remotely exploitable without any authentication or user interaction, increasing its risk profile. The CVSS v3.1 base score of 7.5 reflects the high severity due to network attack vector, low attack complexity, no privileges required, and no user interaction needed. The vulnerability does not compromise confidentiality or integrity but solely impacts availability. No public exploits have been reported yet, and software versions beyond End of Technical Support (EoTS) are not evaluated. The absence of patch links suggests that fixes may be forthcoming or in development. The root cause relates to improper handling of resources after they have expired or been released, leading to unstable TMM behavior when processing HTTP/2 traffic under specific security policy configurations.

For European organizations, the primary impact of CVE-2025-55669 is service disruption due to denial of service on F5 BIG-IP devices. These devices are widely used in enterprise and critical infrastructure environments for load balancing, application delivery, and security enforcement. A TMM crash can lead to downtime of web applications, internal services, or security gateways, potentially affecting business continuity and operational resilience. Although confidentiality and integrity are not directly impacted, availability loss can indirectly affect compliance with regulations such as GDPR, especially if services become unavailable to customers or partners. Organizations relying on BIG-IP for securing HTTP/2 traffic with Advanced WAF and ASM policies are particularly vulnerable. The lack of authentication or user interaction required for exploitation means attackers can remotely trigger the DoS, increasing the risk of automated or large-scale attacks. This could be leveraged by threat actors to disrupt services during geopolitical tensions or cyber campaigns targeting European entities. The impact is heightened in sectors such as finance, telecommunications, government, and healthcare, where BIG-IP devices are commonly deployed.

1. Monitor vendor communications closely for official patches or updates addressing CVE-2025-55669 and apply them promptly once available. 2. Temporarily disable or avoid using server-side HTTP/2 profiles on virtual servers that have Advanced WAF and ASM policies enabled, if business operations allow. 3. Implement network-level protections such as rate limiting or filtering to detect and block anomalous or malformed HTTP/2 traffic that could trigger the vulnerability. 4. Regularly monitor the stability and logs of the Traffic Management Microkernel (TMM) to detect early signs of crashes or abnormal terminations. 5. Consider deploying redundant BIG-IP devices or failover configurations to minimize service disruption in case of TMM termination. 6. Conduct internal security assessments and penetration testing focusing on HTTP/2 traffic handling and WAF/ASM configurations to identify potential exploitation vectors. 7. Engage with F5 support for guidance on configuration best practices that reduce exposure to this vulnerability. 8. Ensure incident response plans include procedures for rapid recovery from BIG-IP service interruptions.