CVE-2025-54109 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). The flaw exists within the Windows Defender Firewall Service, where improper handling of resource types leads to type confusion. This vulnerability allows an authorized local attacker—someone with existing privileges on the system—to exploit the flaw to elevate their privileges further. Specifically, the attacker can leverage this bug to gain higher system privileges than originally granted, potentially achieving SYSTEM-level access. The vulnerability does not require user interaction but does require the attacker to have some level of local access (indicated by CVSS vector AV:L and PR:H). The CVSS v3.1 base score is 6.7, categorized as medium severity, reflecting a significant impact on confidentiality, integrity, and availability (all rated high in the vector). No known exploits are currently reported in the wild, and no official patches have been linked yet. The vulnerability was reserved in mid-July 2025 and published in early September 2025, indicating recent discovery and disclosure. The technical root cause is a type confusion error, which typically arises when a program incorrectly interprets a data type, leading to unexpected behavior and potential security breaches. In this case, the Windows Defender Firewall Service incorrectly accesses resources using incompatible types, enabling privilege escalation. This vulnerability is particularly relevant for environments still running Windows 10 Version 1809, which is an older release with extended support but not the latest feature updates. Organizations relying on this version are at risk if local attackers can gain initial access, such as through compromised user accounts or insider threats.

For European organizations, the impact of CVE-2025-54109 can be significant, especially in sectors where Windows 10 Version 1809 remains in use, such as industrial control systems, legacy enterprise environments, or government agencies with strict update policies. Successful exploitation allows attackers with local access to escalate privileges, potentially leading to full system compromise. This can result in unauthorized data access, disruption of critical services, and the ability to deploy further malware or ransomware with elevated rights. Given the high confidentiality, integrity, and availability impact, sensitive data could be exposed or altered, and system stability compromised. The lack of user interaction requirement means that once local access is obtained, exploitation can be automated or executed stealthily. Although no known exploits are currently in the wild, the medium severity score and nature of the vulnerability suggest that attackers may develop exploits, increasing risk over time. European organizations with strict regulatory requirements (e.g., GDPR) must consider the potential for data breaches and operational disruptions. The threat is heightened in environments where endpoint security relies heavily on Windows Defender Firewall Service and where patching legacy systems is delayed.

To mitigate CVE-2025-54109 effectively, European organizations should: 1) Prioritize upgrading from Windows 10 Version 1809 to a more recent, supported Windows version that includes security improvements and patches. 2) Implement strict local access controls and monitoring to limit the ability of unauthorized users to gain initial access, including enforcing least privilege principles and using multi-factor authentication for local accounts. 3) Employ application whitelisting and endpoint detection and response (EDR) solutions to detect unusual privilege escalation attempts or anomalous behavior related to the Windows Defender Firewall Service. 4) Monitor system logs and security event data for signs of exploitation attempts targeting firewall services or privilege escalation patterns. 5) If upgrading is not immediately feasible, consider isolating legacy systems from critical networks and sensitive data to reduce exposure. 6) Stay alert for official patches or security advisories from Microsoft and apply them promptly once available. 7) Conduct regular security awareness training to reduce insider threats and ensure that authorized users understand the risks of privilege misuse. These steps go beyond generic advice by focusing on controlling local access vectors, monitoring specific service behavior, and managing legacy system risks.