CVE-2025-26636 is a medium-severity vulnerability identified in Microsoft Windows Server 2025, specifically affecting the Server Core installation version 10.0.26100.0. The vulnerability arises from processor optimization processes that remove or modify security-critical code within the Windows Kernel. This alteration can inadvertently expose sensitive information to an attacker who has authorized local access to the system. The vulnerability is categorized under CWE-1037, which relates to the removal or modification of security-critical code due to processor optimizations. Exploitation does not require user interaction but does require the attacker to have local privileges (PR:L), indicating that the attacker must already have some level of access to the system. The attack vector is local (AV:L), and the vulnerability impacts confidentiality (C:H) without affecting integrity or availability. The CVSS v3.1 base score is 5.5, reflecting a medium severity level. No known exploits are currently reported in the wild, and no patches have been linked yet. The vulnerability could allow an authorized local attacker to disclose sensitive information by leveraging the altered kernel code paths caused by processor optimizations, potentially leading to information leakage that could be used for further attacks or privilege escalation.

For European organizations, this vulnerability poses a risk primarily to environments running Windows Server 2025 Server Core installations, which are often used in data centers and cloud infrastructure due to their minimal footprint and reduced attack surface. The information disclosure could compromise sensitive data, including system configurations, credentials, or other protected information stored or processed by the kernel. This could facilitate subsequent attacks such as privilege escalation or lateral movement within networks. Given the local access requirement, the threat is more significant in environments where multiple users have access to server systems or where attackers could gain initial footholds through other means (e.g., phishing or compromised credentials). The impact on confidentiality is high, but since integrity and availability are not affected, the immediate operational disruption risk is lower. However, the potential for information leakage could undermine compliance with European data protection regulations such as GDPR, especially if personal or sensitive data is exposed. Organizations relying on Windows Server 2025 for critical infrastructure or hosting sensitive applications should consider this vulnerability seriously.

To mitigate this vulnerability, European organizations should: 1) Restrict local access to Windows Server 2025 Server Core installations strictly to trusted and authorized personnel only, minimizing the risk of an attacker gaining the required local privileges. 2) Implement robust monitoring and auditing of local access and kernel-level activities to detect any anomalous behavior that could indicate exploitation attempts. 3) Apply the principle of least privilege rigorously, ensuring that users and services operate with minimal necessary permissions to limit the potential impact of local exploits. 4) Stay vigilant for official patches or updates from Microsoft addressing this vulnerability and prioritize their deployment as soon as they become available. 5) Consider deploying additional endpoint protection solutions capable of detecting unusual kernel modifications or information disclosure attempts. 6) Review and harden system configurations to reduce the attack surface, including disabling unnecessary services and features on Server Core installations. 7) Conduct regular security assessments and penetration testing focused on local privilege escalation and information disclosure vectors to identify and remediate potential weaknesses proactively.