CVE-2025-21373 is a vulnerability identified in Microsoft Windows 10 Version 1809 (build 10.0.17763.0) related to improper link resolution before file access, classified under CWE-59 ('Link Following'). This vulnerability arises when Windows Installer improperly handles symbolic links or junction points before accessing files, allowing an attacker with limited privileges to manipulate the link target. By exploiting this flaw, an attacker can cause the system to execute or modify files with elevated privileges, effectively escalating their rights on the system. The vulnerability does not require user interaction but does require local access and some level of privileges (low privileges). The CVSS 3.1 base score is 7.8, reflecting high impact on confidentiality, integrity, and availability, with low attack complexity and privileges required. No public exploits are known yet, but the vulnerability's nature makes it a candidate for future exploitation, especially in environments where Windows 10 Version 1809 is still in use. The absence of patch links suggests that a fix may be pending or in development. This vulnerability is particularly concerning because Windows Installer is a core component used widely for software installation and maintenance, and exploitation could lead to full system compromise.

For European organizations, the impact of CVE-2025-21373 can be significant. Many enterprises and public sector entities still operate legacy Windows 10 Version 1809 systems due to compatibility or operational constraints. Exploitation could allow attackers to elevate privileges locally, bypassing security controls and gaining administrative access. This can lead to unauthorized data access, system manipulation, deployment of malware or ransomware, and disruption of critical services. Confidentiality breaches could expose sensitive personal or business data, violating GDPR and other data protection regulations. Integrity and availability impacts could disrupt business operations, especially in sectors like finance, healthcare, and critical infrastructure. The lack of known exploits currently provides a window for proactive mitigation, but the vulnerability's characteristics make it attractive for attackers targeting legacy systems.

Organizations should prioritize upgrading affected systems to a supported and patched Windows version as soon as patches become available from Microsoft. Until patches are released, restrict local access to systems running Windows 10 Version 1809, especially limiting access to untrusted users or processes. Employ application whitelisting and endpoint detection and response (EDR) solutions to monitor and block suspicious Windows Installer activities, such as unexpected installation or modification attempts. Review and harden permissions on directories and symbolic links to prevent unauthorized link manipulation. Conduct regular audits of installed software and system configurations to detect anomalies. Additionally, implement network segmentation to isolate legacy systems and reduce the attack surface. Educate IT staff about this vulnerability to ensure rapid response once patches are released.