CVE-2026-25187 is a vulnerability in Microsoft Windows 10 Version 1607 (build 14393.0) related to improper link resolution before file access, also known as 'link following,' within the Winlogon process. Winlogon is a critical Windows component responsible for handling user logins and session management. The flaw allows an authorized local attacker with limited privileges to manipulate symbolic links or junction points that Winlogon follows before accessing files. By exploiting this improper link resolution, the attacker can redirect Winlogon to access or modify files they should not have permission to, thereby escalating their privileges to higher levels, potentially SYSTEM. The vulnerability is categorized under CWE-59, which involves improper handling of symbolic links leading to unauthorized file access. The CVSS v3.1 base score is 7.8, reflecting high severity due to the impact on confidentiality, integrity, and availability, ease of exploitation with low attack complexity, and no requirement for user interaction. Although no known exploits are currently reported in the wild, the vulnerability poses a significant risk to systems still running this legacy Windows 10 version. The absence of an official patch at the time of publication means organizations must rely on interim mitigations and plan for upgrades. This vulnerability highlights the risks associated with legacy OS versions and the importance of secure handling of file system links in privileged processes.

The exploitation of CVE-2026-25187 allows a local attacker with limited privileges to escalate to higher privileges, potentially SYSTEM level, on affected Windows 10 Version 1607 systems. This can lead to full system compromise, enabling the attacker to install malware, access sensitive data, modify system configurations, or disrupt system availability. The impact extends to confidentiality, integrity, and availability of the affected systems. Organizations relying on legacy Windows 10 environments, especially in critical infrastructure, government, healthcare, and enterprise sectors, face increased risk of targeted attacks leveraging this vulnerability. The ability to escalate privileges locally can facilitate lateral movement within networks, increasing the threat surface. Although no exploits are currently known in the wild, the high severity and ease of exploitation make this a significant threat if weaponized. The lack of patches further exacerbates the risk, potentially leading to prolonged exposure.

1. Restrict local user permissions to the minimum necessary, preventing untrusted users from creating or manipulating symbolic links or junction points in sensitive directories. 2. Implement strict monitoring and alerting on file system changes, especially creation or modification of symbolic links in directories accessed by Winlogon or other privileged processes. 3. Employ application whitelisting and endpoint protection solutions capable of detecting suspicious link-following behaviors or privilege escalation attempts. 4. Where feasible, upgrade affected systems from Windows 10 Version 1607 to a supported and patched Windows version to eliminate exposure. 5. Apply any forthcoming official patches from Microsoft promptly once released. 6. Conduct regular audits of local accounts and privileges to reduce the number of users capable of local exploitation. 7. Use Group Policy or security baselines to harden system configurations related to file system access and symbolic link handling. 8. Educate system administrators about the risks of legacy OS usage and the importance of timely patching and upgrades.