CVE-2025-54915 is a vulnerability classified under CWE-843 (Access of Resource Using Incompatible Type, commonly known as 'Type Confusion') affecting Microsoft Windows 10 Version 1809 (build 10.0.17763.0). This flaw exists within the Windows Defender Firewall Service, a critical component responsible for filtering network traffic and enforcing security policies on Windows systems. The vulnerability allows an authorized local attacker—someone with existing privileges on the system—to exploit type confusion in the firewall service's handling of resources. Type confusion occurs when a program accesses a resource or object using an incorrect or incompatible data type, potentially leading to unexpected behavior such as memory corruption or privilege escalation. In this case, the attacker can leverage this flaw to elevate their privileges locally, gaining higher-level access than originally permitted. The CVSS v3.1 base score is 6.7 (medium severity), reflecting that exploitation requires local access with high privileges (PR:H), no user interaction (UI:N), and results in high impact on confidentiality, integrity, and availability (C:H/I:H/A:H). No known exploits are currently reported in the wild, and no official patches have been linked yet. However, the vulnerability's presence in a widely deployed OS version means it poses a significant risk if weaponized. Since Windows Defender Firewall is a core security component, exploitation could allow attackers to disable or bypass firewall protections, manipulate network traffic, or execute arbitrary code with elevated privileges, severely compromising system security.

For European organizations, this vulnerability presents a substantial risk, particularly for enterprises and government agencies still operating legacy Windows 10 Version 1809 systems. Successful exploitation could allow attackers with local access—such as malicious insiders or attackers who have gained initial foothold via other means—to escalate privileges and fully compromise affected machines. This could lead to unauthorized access to sensitive data, disruption of critical services, and lateral movement within corporate networks. Given the firewall service's role, attackers might disable or alter firewall rules, increasing exposure to external threats. Organizations in sectors with strict data protection requirements (e.g., finance, healthcare, public administration) could face regulatory repercussions if breaches occur. Moreover, the medium severity score and lack of known exploits suggest this vulnerability might be targeted in the near future, especially as attackers often chain privilege escalation bugs with initial access exploits. The impact is amplified in environments where Windows 10 1809 remains in use due to compatibility or upgrade delays, common in some European enterprises with legacy infrastructure.

To mitigate this vulnerability effectively, European organizations should: 1) Prioritize upgrading affected systems to a more recent, supported Windows 10 version or Windows 11, as Windows 10 Version 1809 is nearing or past end-of-support, reducing exposure to unpatched vulnerabilities. 2) Implement strict access controls to limit local administrative privileges, minimizing the pool of users who could exploit this flaw. 3) Employ application whitelisting and endpoint detection and response (EDR) solutions to detect anomalous behavior indicative of privilege escalation attempts. 4) Monitor Windows Defender Firewall service logs and system event logs for unusual activity or crashes that might signal exploitation attempts. 5) Segment networks to contain potential compromises and restrict lateral movement from affected hosts. 6) Stay alert for official patches or security advisories from Microsoft and apply them promptly once available. 7) Conduct regular vulnerability assessments and penetration testing focusing on privilege escalation vectors to identify and remediate similar weaknesses proactively.