CVE-2025-21304 is a high-severity use-after-free vulnerability (CWE-416) found in the Microsoft Desktop Window Manager (DWM) Core Library on Windows 10 Version 1809 (build 10.0.17763.0). The vulnerability allows an attacker with limited privileges (low-level privileges) to elevate their privileges on the affected system. Specifically, the flaw arises when the DWM Core Library improperly manages memory, leading to a use-after-free condition. This memory corruption can be exploited to execute arbitrary code with elevated privileges, potentially granting the attacker full control over the system. The vulnerability does not require user interaction, and the attack vector is local (AV:L), meaning the attacker must have access to the system but can operate without additional user involvement. The CVSS v3.1 score of 7.8 reflects the high impact on confidentiality, integrity, and availability, as successful exploitation can lead to complete system compromise. No known exploits are currently reported in the wild, and no official patches have been linked yet, indicating the need for vigilance and proactive mitigation. The vulnerability is particularly critical because Windows 10 Version 1809 is still in use in some environments, especially where legacy systems are maintained. The lack of user interaction and the ability to escalate privileges make this vulnerability a significant threat to endpoint security.

For European organizations, this vulnerability poses a substantial risk, especially in sectors relying on legacy Windows 10 Version 1809 deployments, such as manufacturing, healthcare, and government agencies. Exploitation could lead to unauthorized access to sensitive data, disruption of critical services, and potential lateral movement within corporate networks. The elevation of privilege can enable attackers to bypass security controls, install persistent malware, or exfiltrate confidential information. Given the high confidentiality, integrity, and availability impact, organizations could face operational downtime, regulatory penalties under GDPR for data breaches, and reputational damage. The local attack vector implies that insider threats or attackers who gain initial foothold through other means (e.g., phishing, physical access) could leverage this vulnerability to escalate privileges and deepen their access. The absence of known exploits in the wild offers a window for preemptive action, but also means attackers may develop exploits soon after disclosure, increasing urgency for mitigation.

1. Upgrade or patch: Although no official patch link is provided yet, organizations should monitor Microsoft security advisories closely and apply patches immediately upon release. 2. Upgrade OS: Where feasible, upgrade systems from Windows 10 Version 1809 to a supported and updated Windows version to eliminate exposure. 3. Restrict local access: Limit local user accounts with low privileges and enforce strict access controls to reduce the risk of local exploitation. 4. Application whitelisting: Implement application control policies to prevent unauthorized code execution, which can mitigate exploitation attempts. 5. Endpoint detection and response (EDR): Deploy EDR solutions capable of detecting suspicious memory corruption behaviors and privilege escalation attempts. 6. Network segmentation: Isolate critical systems to limit lateral movement if an attacker exploits this vulnerability. 7. User privilege management: Enforce the principle of least privilege to minimize the impact of compromised accounts. 8. Monitor logs: Enable detailed logging and monitor for unusual privilege escalation activities or DWM-related errors. 9. Incident response readiness: Prepare response plans for potential exploitation scenarios involving privilege escalation on Windows endpoints.