CVE-2025-26678 is a vulnerability classified under CWE-284 (Improper Access Control) found in Microsoft Windows 10 Version 1809, specifically targeting Windows Defender Application Control (WDAC). WDAC is a security feature designed to enforce application whitelisting policies, preventing unauthorized or malicious code execution. This vulnerability allows an attacker with local access but no privileges (no authentication required) to bypass WDAC protections, effectively undermining the integrity and security posture of the system. The attacker does not require user interaction, making exploitation more straightforward once local access is obtained. The CVSS 3.1 base score of 8.4 reflects the high impact on confidentiality, integrity, and availability, combined with low attack complexity and no privileges required. Although no public exploits are known yet, the vulnerability's nature suggests that attackers could leverage it to run unauthorized code, escalate privileges, or disable security controls. The affected version is Windows 10 1809 (build 10.0.17763.0), which is an older release but still in use in some environments. No patches or mitigations have been officially released at the time of publication, increasing the urgency for defensive measures.

For European organizations, this vulnerability poses a significant risk, especially for those relying on Windows 10 Version 1809 in operational environments where WDAC is deployed to enforce strict application control policies. Successful exploitation could lead to unauthorized code execution, data breaches, and disruption of critical services. The compromise of WDAC undermines a key security layer, potentially allowing malware or insider threats to bypass application whitelisting. This is particularly concerning for sectors such as finance, healthcare, government, and critical infrastructure, where data confidentiality and system integrity are paramount. The local attack vector means that physical or remote local access to machines is required, which could be feasible in environments with shared workstations or insufficient endpoint security. The lack of user interaction and privileges needed makes this vulnerability easier to exploit once access is gained, increasing the threat level. Given the widespread use of Windows 10 in Europe, the potential impact is broad, affecting both private and public sector entities.

1. Restrict local access to systems running Windows 10 Version 1809, enforcing strict physical and logical access controls. 2. Implement robust endpoint detection and response (EDR) solutions to monitor for unusual activity indicative of WDAC bypass attempts. 3. Enforce network segmentation to limit lateral movement if local access is compromised. 4. Prioritize upgrading affected systems to newer, supported Windows versions where this vulnerability is patched or does not exist. 5. Apply principle of least privilege to user accounts to reduce the risk of local exploitation. 6. Monitor Windows event logs and WDAC logs for anomalies or unauthorized policy changes. 7. Prepare incident response plans specifically addressing potential WDAC bypass scenarios. 8. Stay alert for official patches or updates from Microsoft and apply them promptly once available.