CVE-2025-55687 is a race condition vulnerability classified under CWE-362 affecting the Windows Resilient File System (ReFS) component in Microsoft Windows 11 Version 25H2 (build 10.0.26200.0). The flaw arises from improper synchronization when multiple threads or processes concurrently access shared resources within ReFS, leading to a state where an unauthorized local attacker can exploit this timing issue to elevate privileges. This vulnerability does not require prior privileges or user interaction, but the attack complexity is high due to the need to precisely trigger the race condition. Successful exploitation can lead to full compromise of system confidentiality, integrity, and availability by allowing the attacker to execute code with elevated privileges or manipulate system files. The vulnerability was reserved in August 2025 and published in October 2025, with no known exploits in the wild at the time of publication. The CVSS v3.1 score of 7.4 (AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H) indicates a high-severity issue with local attack vector, high attack complexity, no privileges required, no user interaction, and full impact on confidentiality, integrity, and availability. The lack of available patches at the time suggests organizations must rely on interim mitigations until updates are released by Microsoft.

European organizations running Windows 11 Version 25H2 with ReFS volumes face significant risk from this vulnerability. Exploitation can lead to local privilege escalation, enabling attackers to gain administrative control over affected systems. This could result in unauthorized access to sensitive data, disruption of critical services, and potential lateral movement within enterprise networks. Sectors such as finance, healthcare, government, and critical infrastructure, which often use Windows 11 and may utilize ReFS for data integrity and resilience, are particularly vulnerable. The high impact on confidentiality, integrity, and availability means that successful exploitation could lead to data breaches, system outages, and loss of trust. Given the local attack vector, insider threats or attackers with limited local access could leverage this vulnerability to escalate privileges and compromise entire networks. The absence of known exploits currently provides a window for proactive defense, but the high severity necessitates urgent attention.

1. Apply official Microsoft patches immediately once they become available to address the race condition in ReFS. 2. Until patches are released, restrict local access to systems running Windows 11 25H2, especially those with ReFS volumes, by enforcing strict access controls and limiting user permissions. 3. Monitor system logs and behavior for unusual local activity indicative of privilege escalation attempts, focusing on file system operations related to ReFS. 4. Employ endpoint detection and response (EDR) solutions capable of detecting anomalous process behavior or race condition exploitation techniques. 5. Consider temporarily disabling or limiting the use of ReFS volumes if feasible, or isolating systems that require ReFS to reduce exposure. 6. Educate system administrators and security teams about the vulnerability specifics to enhance detection and response readiness. 7. Implement network segmentation to contain potential lateral movement from compromised local accounts. 8. Maintain up-to-date backups and test recovery procedures to mitigate impact of potential attacks exploiting this vulnerability.