CVE-2025-54109 is a vulnerability classified under CWE-843 (Access of Resource Using Incompatible Type, or type confusion) found in the Windows Defender Firewall Service component of Microsoft Windows 10 Version 1809 (build 10.0.17763.0). The flaw allows an attacker who already has local authorized access with high privileges to exploit the type confusion to elevate their privileges further on the affected system. Type confusion vulnerabilities occur when a program accesses a resource using a type that is incompatible with the actual type of the resource, potentially leading to memory corruption or unauthorized access. In this case, the Windows Defender Firewall Service improperly handles resource types, enabling privilege escalation. The CVSS v3.1 base score is 6.7, reflecting a medium severity with attack vector local, low attack complexity, required privileges high, no user interaction, and impacts on confidentiality, integrity, and availability. No public exploits or patches are currently available, but the vulnerability is officially published and reserved since July 2025. The affected Windows 10 version 1809 is an older release but still present in some enterprise environments, especially those with slower upgrade cycles or legacy application dependencies. This vulnerability could be leveraged by attackers to gain SYSTEM-level privileges from an already authorized local account, potentially allowing full system compromise, installation of persistent malware, or disabling security controls.

For European organizations, the impact of CVE-2025-54109 can be significant in environments where Windows 10 Version 1809 is still deployed, particularly in sectors with strict regulatory requirements such as finance, healthcare, and government. Successful exploitation could lead to unauthorized privilege escalation, enabling attackers to bypass security controls, access sensitive data, modify system configurations, or disrupt availability. This could result in data breaches, operational downtime, and compliance violations under GDPR and other regulations. Since the vulnerability requires local access with high privileges, the primary risk vector is through insider threats, compromised accounts, or lateral movement after initial breach. Organizations with legacy systems or delayed patching practices are at higher risk. The lack of known exploits in the wild currently reduces immediate threat but does not eliminate future risk, especially as exploit development could emerge. The impact on confidentiality, integrity, and availability is high if exploited, making timely mitigation critical to prevent escalation from local attackers to full system compromise.

1. Prioritize upgrading affected systems from Windows 10 Version 1809 to a supported, more recent Windows 10 or Windows 11 version to eliminate exposure to this vulnerability. 2. Apply any security updates or patches Microsoft releases addressing CVE-2025-54109 as soon as they become available. 3. Restrict local administrative privileges to the minimum necessary users and accounts to reduce the pool of potential attackers who can exploit this vulnerability. 4. Implement strict access controls and monitoring on systems running Windows 10 1809, including auditing privilege escalation attempts and unusual process behavior related to the Windows Defender Firewall Service. 5. Use endpoint detection and response (EDR) solutions to detect suspicious activities indicative of privilege escalation or exploitation attempts. 6. Enforce multi-factor authentication and strong credential hygiene to reduce risk of account compromise that could lead to local access. 7. Conduct regular vulnerability assessments and penetration testing focusing on privilege escalation vectors to identify and remediate weaknesses proactively. 8. Educate IT and security teams about this vulnerability and the importance of patch management and least privilege principles.