CVE-2025-54109 is a vulnerability identified in the Windows Defender Firewall Service component of Microsoft Windows 10 Version 1809 (build 10.0.17763.0). The flaw is classified as a type confusion vulnerability (CWE-843), where the system incorrectly accesses a resource using an incompatible type. This type confusion can lead to unexpected behavior, allowing an attacker with authorized local access and high privileges to escalate their privileges further on the affected system. The vulnerability does not require user interaction and has a CVSS 3.1 base score of 6.7, indicating medium severity. The attack vector is local (AV:L), with low attack complexity (AC:L), but requires the attacker to already have high privileges (PR:H). The impact on confidentiality, integrity, and availability is rated high, meaning successful exploitation could compromise sensitive data, alter system configurations, or disrupt service availability. Currently, there are no known exploits in the wild, and no patches have been linked yet, but the vulnerability is publicly disclosed and should be addressed promptly. The flaw resides in a core security component, Windows Defender Firewall Service, which is critical for network traffic filtering and system protection, making this vulnerability significant for maintaining system security.

For European organizations, this vulnerability poses a risk primarily to systems still running Windows 10 Version 1809, which may be found in legacy environments, industrial control systems, or organizations with delayed patch management. Successful exploitation could allow attackers with local access to elevate privileges, potentially leading to full system compromise, unauthorized access to sensitive information, and disruption of firewall protections. This could impact confidentiality by exposing sensitive data, integrity by allowing unauthorized changes to system configurations or security policies, and availability by disabling or manipulating firewall services. Critical sectors such as government, finance, healthcare, and critical infrastructure in Europe could face increased risks if legacy systems remain unpatched. Additionally, organizations with remote access solutions that allow local execution of code could be indirectly affected. The lack of known exploits in the wild reduces immediate risk but does not eliminate the threat, especially as attackers may develop exploits following public disclosure.

1. Prioritize upgrading or patching Windows 10 Version 1809 systems to a supported and updated Windows version as Microsoft may release a security update addressing this vulnerability. 2. Until patches are available, restrict local administrative access to trusted personnel only, minimizing the risk of privilege escalation. 3. Employ application whitelisting and endpoint detection and response (EDR) solutions to monitor and block suspicious activities related to privilege escalation attempts. 4. Regularly audit and review user privileges and remove unnecessary high privilege accounts to reduce the attack surface. 5. Implement strict network segmentation to limit lateral movement if an attacker gains local access. 6. Monitor system and firewall logs for anomalies that could indicate exploitation attempts. 7. Educate IT staff about this vulnerability and ensure incident response plans include scenarios involving local privilege escalation. 8. Consider deploying host-based firewalls or security solutions that can provide additional layers of defense beyond the Windows Defender Firewall Service.