CVE-2025-55679 is a vulnerability identified in Microsoft Windows 11 Version 25H2 (build 10.0.26200.0) involving improper input validation within the Windows Kernel. The weakness stems from the kernel's failure to adequately validate input data, which can be manipulated by an unauthorized local attacker to disclose sensitive information from kernel memory. This vulnerability is classified under CWE-20 (Improper Input Validation) and is related to information disclosure risks (CWE-200). The CVSS v3.1 base score is 5.1, indicating a medium severity level, with the vector string CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C. This means the attack requires local access (AV:L), has high attack complexity (AC:H), does not require privileges (PR:N) or user interaction (UI:N), and impacts confidentiality (C:H) without affecting integrity or availability. The scope remains unchanged (S:U). No known exploits have been reported in the wild, and no official patches have been released yet. The vulnerability could allow attackers with local access to extract sensitive kernel information, potentially aiding further attacks or privilege escalation attempts. Given the kernel-level nature, the flaw is critical to address promptly once mitigations or patches become available. The lack of remote exploitability and the high complexity reduce immediate risk but do not eliminate the threat in environments where local access is possible.

For European organizations, this vulnerability poses a confidentiality risk by potentially exposing sensitive kernel memory information to unauthorized local users. This could facilitate further attacks, such as privilege escalation or bypassing security controls, especially in environments with shared or multi-user systems. Critical sectors like finance, government, healthcare, and industrial control systems that rely heavily on Windows 11 25H2 could face increased risk if attackers gain local access. The impact is mitigated somewhat by the requirement for local access and high attack complexity, but insider threats or compromised endpoints could exploit this flaw. Data confidentiality breaches could lead to regulatory non-compliance under GDPR, reputational damage, and operational disruptions if attackers leverage disclosed information for subsequent attacks. The absence of known exploits reduces immediate threat levels but does not preclude targeted attacks in sensitive environments.

European organizations should implement strict local access controls, ensuring only authorized personnel can access Windows 11 25H2 systems. Employ endpoint detection and response (EDR) solutions to monitor for unusual local activity indicative of exploitation attempts. Use application whitelisting and privilege management to limit the ability of unprivileged users to execute potentially malicious code. Regularly audit and harden system configurations to reduce attack surface, including disabling unnecessary local accounts and services. Prepare for timely deployment of official patches from Microsoft once released, and test updates in controlled environments before wide rollout. Employ network segmentation to isolate critical systems and reduce the risk of lateral movement. Educate users about the risks of local compromise and enforce strong physical security controls to prevent unauthorized device access. Consider deploying kernel integrity monitoring tools to detect anomalous behavior at the kernel level.