CVE-2025-26678 is a high-severity vulnerability affecting Microsoft Windows 10 Version 1809 (build 10.0.17763.0). The flaw resides in Windows Defender Application Control (WDAC), a security feature designed to restrict unauthorized applications from executing on a system. Specifically, this vulnerability is classified under CWE-284, indicating improper access control. An unauthorized attacker with local access can exploit this vulnerability to bypass WDAC protections without requiring any privileges or user interaction. This bypass could allow execution of malicious code or unauthorized applications that WDAC would normally block, potentially leading to full compromise of the affected system. The CVSS v3.1 base score is 8.4, reflecting high impact on confidentiality, integrity, and availability, with low attack complexity and no privileges or user interaction required. Although no known exploits are currently reported in the wild, the vulnerability's nature and severity suggest it could be leveraged for local privilege escalation or persistence by adversaries who have gained initial access. The vulnerability was publicly disclosed on April 8, 2025, with no patch links currently available, indicating that mitigation options may be limited until an official update is released by Microsoft. Organizations running Windows 10 Version 1809 should be aware of this risk, especially in environments where local access controls are weak or where WDAC is a critical component of endpoint security strategy.

For European organizations, the impact of CVE-2025-26678 could be significant, particularly in sectors that rely heavily on Windows 10 Version 1809 and use WDAC as part of their defense-in-depth strategy. Successful exploitation allows attackers to bypass application control policies, potentially enabling execution of unauthorized or malicious software. This can lead to data breaches, ransomware deployment, or disruption of critical services. Confidentiality, integrity, and availability of sensitive data and systems could be severely compromised. The vulnerability is especially concerning for organizations with shared or multi-user systems, such as public sector offices, healthcare institutions, and manufacturing plants, where local access might be easier to obtain. The lack of required privileges or user interaction lowers the barrier for exploitation once local access is achieved, increasing the risk of lateral movement and persistence within networks. Additionally, the absence of known exploits in the wild currently provides a window for proactive mitigation, but also means organizations must be vigilant for emerging threats leveraging this vulnerability.

Given the absence of an official patch at the time of disclosure, European organizations should implement layered mitigation strategies. First, restrict local access to systems running Windows 10 Version 1809 by enforcing strict physical security and limiting user permissions to the minimum necessary. Employ endpoint detection and response (EDR) tools to monitor for unusual process execution or attempts to bypass WDAC policies. Consider disabling or tightening WDAC policies temporarily if feasible, or applying additional application whitelisting controls through alternative security solutions. Network segmentation can limit the impact of compromised endpoints. Organizations should prioritize upgrading affected systems to newer, supported Windows versions where this vulnerability is not present or patched. Regularly review and audit local user accounts and access rights to minimize the attack surface. Finally, maintain up-to-date backups and incident response plans to quickly recover from potential exploitation.