CVE-2025-21183 is a vulnerability identified in the Windows Resilient File System (ReFS) Deduplication Service on Windows 11 Version 24H2 (build 10.0.26100.0). The issue is a double free condition (CWE-415), where the system erroneously frees memory twice, leading to memory corruption. This flaw can be exploited by an attacker with local access to the system to elevate privileges, potentially gaining SYSTEM-level rights. The vulnerability does not require prior authentication or user interaction, but the attack complexity is high, indicating that exploitation demands specialized conditions or knowledge. The ReFS Deduplication Service is responsible for optimizing storage by eliminating duplicate data blocks, and the flaw resides in its memory management routines. While no public exploits have been reported, the vulnerability's impact includes full compromise of confidentiality, integrity, and availability of affected systems. The CVSS v3.1 score is 7.4, reflecting high severity with attack vector local, attack complexity high, no privileges required, and no user interaction. The vulnerability was reserved in December 2024 and published in February 2025, with no patches currently linked, suggesting that mitigation is pending. Organizations running Windows 11 24H2 with ReFS deduplication enabled should monitor for patches and consider temporary mitigations to restrict local access and reduce attack surface.

The vulnerability allows an attacker with local access to escalate privileges to SYSTEM level, potentially leading to complete system compromise. This can result in unauthorized access to sensitive data, modification or deletion of critical files, and disruption of system availability. In environments where ReFS is used for storage deduplication, such as enterprise servers and workstations, the impact is significant as it undermines the security boundary between users and the operating system. The flaw could be leveraged to bypass security controls, implant persistent malware, or move laterally within networks. Although exploitation complexity is high and no known exploits exist yet, the potential damage warrants urgent attention. Organizations relying on Windows 11 24H2, especially those using ReFS for data deduplication in critical infrastructure, cloud services, or enterprise environments, face elevated risk. The lack of authentication and user interaction requirements means that any local user or malware with local code execution capabilities could attempt exploitation.

1. Monitor Microsoft security advisories closely and apply official patches immediately once released. 2. Restrict local access to systems running Windows 11 Version 24H2, especially those using ReFS deduplication, by enforcing strict access controls and limiting administrative privileges. 3. Disable or limit the use of ReFS deduplication service if feasible until patches are available, particularly on high-risk or critical systems. 4. Employ endpoint detection and response (EDR) solutions to monitor for suspicious local privilege escalation attempts and anomalous memory corruption behaviors. 5. Conduct regular system audits to identify unauthorized local users or processes that could exploit this vulnerability. 6. Use application whitelisting and privilege management to reduce the risk of local code execution by untrusted users. 7. Educate IT staff about the vulnerability and ensure incident response plans include scenarios involving local privilege escalation. 8. Consider network segmentation to isolate critical Windows 11 24H2 systems to minimize lateral movement opportunities.