CVE-2025-21182 is a vulnerability identified in the Windows Resilient File System (ReFS) Deduplication Service component of Windows Server 2025, specifically in Server Core installations. The root cause is a double free error (CWE-415), where the system attempts to free the same memory location 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 has a CVSS v3.1 base score of 7.4, indicating high severity. The attack vector is local (AV:L), with high attack complexity (AC:H), no privileges required (PR:N), and no user interaction (UI:N). The scope is unchanged (S:U), but the impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H). The vulnerability was reserved in December 2024 and published in February 2025. No public exploits have been reported yet, but the nature of the vulnerability suggests that exploitation could allow attackers to bypass security boundaries within the server, potentially leading to full system compromise. The affected version is 10.0.26100.0 of Windows Server 2025 Server Core, a configuration commonly used in enterprise environments for its reduced attack surface and performance benefits. The lack of patch links indicates that a fix may still be pending or in development, emphasizing the need for vigilance and interim mitigations.

For European organizations, especially those relying on Windows Server 2025 Server Core installations for critical infrastructure, cloud services, or enterprise applications, this vulnerability poses a significant risk. Successful exploitation could allow attackers to escalate privileges from a local user context to SYSTEM level, enabling full control over the affected server. This could lead to unauthorized access to sensitive data, disruption of services, and potential lateral movement within networks. Given the high impact on confidentiality, integrity, and availability, organizations could face data breaches, operational downtime, and compliance violations under regulations such as GDPR. The requirement for local access limits remote exploitation but does not eliminate risk, as insider threats or attackers who gain initial footholds via other means could leverage this vulnerability. The Server Core installation is often used in environments prioritizing security and performance, so a vulnerability here undermines these assumptions and could have cascading effects on dependent services and applications.

1. Restrict local access to Windows Server 2025 Server Core systems to trusted administrators only, using strong authentication and access controls. 2. Monitor and audit local user activities closely to detect any suspicious behavior that could indicate exploitation attempts. 3. Apply the official security patches from Microsoft as soon as they are released; maintain close communication with Microsoft security advisories for updates. 4. Employ application whitelisting and endpoint protection solutions that can detect anomalous behavior related to memory corruption or privilege escalation attempts. 5. Use virtualization-based security features and hardware-enforced isolation where possible to limit the impact of privilege escalation. 6. Implement network segmentation to limit lateral movement if a server is compromised. 7. Conduct regular vulnerability assessments and penetration testing focused on local privilege escalation vectors. 8. Until patches are available, consider disabling or limiting the use of the ReFS Deduplication Service if feasible in your environment to reduce attack surface.