CVE-2025-21367 is a use-after-free vulnerability classified under CWE-416 affecting the Win32 Kernel Subsystem in Microsoft Windows 10 Version 1809 (build 10.0.17763.0). This vulnerability allows an attacker with low privileges (PR:L) and no user interaction (UI:N) to execute an elevation of privilege attack by exploiting a memory corruption flaw in the kernel. The flaw arises when the kernel improperly manages memory objects, leading to a use-after-free condition that can be leveraged to execute arbitrary code with kernel-level privileges. The vulnerability has a CVSS 3.1 base score of 7.8, reflecting high severity with high impact on confidentiality, integrity, and availability (C:H/I:H/A:H). The attack vector is local (AV:L), meaning the attacker must have some access to the system but can escalate privileges without further user interaction. No known exploits have been reported in the wild, and no patches are currently available, though the vulnerability was published on February 11, 2025. The vulnerability's exploitation could allow attackers to bypass security boundaries, gain SYSTEM-level privileges, and fully compromise affected systems. This is particularly critical for environments relying on legacy Windows 10 1809 installations, which are no longer mainstream but may still be in use in some enterprises.

For European organizations, the impact of CVE-2025-21367 is significant. The vulnerability enables local attackers to escalate privileges to SYSTEM level, potentially allowing full control over affected machines. This can lead to unauthorized access to sensitive data, disruption of critical services, and deployment of further malware or ransomware. Organizations with legacy systems running Windows 10 Version 1809, especially in sectors such as finance, healthcare, government, and critical infrastructure, face heightened risks. The compromise of such systems could result in data breaches, operational downtime, and regulatory non-compliance under GDPR due to loss of data confidentiality and integrity. Additionally, the local attack vector means insider threats or attackers who gain initial foothold through other means can leverage this vulnerability to deepen their access. The absence of patches increases the window of exposure, emphasizing the need for proactive mitigation.

Given the lack of official patches, European organizations should prioritize upgrading affected systems to a supported and fully patched version of Windows, such as Windows 10 21H2 or later, or Windows 11. Where immediate upgrade is not feasible, organizations should implement strict access controls to limit local user privileges and reduce the number of users with local login rights. Employ application whitelisting and endpoint detection and response (EDR) solutions to monitor for suspicious kernel-level activities indicative of exploitation attempts. Regularly audit and harden system configurations to minimize attack surface. Network segmentation can help contain potential compromises. Additionally, maintain up-to-date backups and incident response plans to mitigate impact if exploitation occurs. Organizations should monitor Microsoft security advisories closely for forthcoming patches and apply them immediately upon release.