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 to elevate privileges by exploiting the mismatch in expected data types, potentially gaining higher system privileges than originally granted. The vulnerability requires local access with high privileges (PR:H) but does not require user interaction (UI:N). The CVSS v3.1 base score is 6.7, indicating a medium severity level, with high impact on confidentiality, integrity, and availability (C:H/I:H/A:H). The attack vector is local (AV:L), meaning the attacker must have some level of access to the system already. No known exploits are currently reported in the wild, and no patches or mitigation links have been published yet. The vulnerability was reserved in mid-July 2025 and published in early September 2025, indicating recent discovery and disclosure. Given the affected product is Windows 10 Version 1809, which is an older release, the vulnerability primarily impacts systems that have not been updated to newer Windows versions or have extended support agreements. The type confusion flaw in a critical security component like the firewall service poses a significant risk as it could allow privilege escalation, enabling attackers to bypass security controls and potentially execute arbitrary code or manipulate firewall rules to facilitate further attacks.

For European organizations, this vulnerability presents a moderate risk primarily to legacy systems still running Windows 10 Version 1809. Privilege escalation vulnerabilities in security-critical components such as the Windows Defender Firewall Service can lead to unauthorized access to sensitive data, disruption of network security policies, and potential lateral movement within corporate networks. This could compromise confidentiality, integrity, and availability of critical systems. Organizations in sectors with strict regulatory requirements (e.g., finance, healthcare, government) may face compliance risks if such vulnerabilities are exploited. Additionally, the lack of a patch increases the window of exposure, especially in environments where upgrading the OS is delayed due to operational constraints. Although exploitation requires local access with high privileges, insider threats or attackers who have already compromised lower-privileged accounts could leverage this vulnerability to escalate privileges and gain full control over affected systems. This could facilitate deployment of ransomware, data exfiltration, or sabotage of network defenses. The absence of known exploits in the wild currently reduces immediate risk but does not eliminate it, as attackers may develop exploits over time.

1. Prioritize upgrading affected systems from Windows 10 Version 1809 to a more recent, supported Windows version where this vulnerability is not present or has been patched. 2. Implement strict access controls and monitoring to limit local administrative privileges and detect anomalous privilege escalation attempts. 3. Use endpoint detection and response (EDR) solutions to monitor Windows Defender Firewall Service behavior and alert on suspicious activity. 4. Apply principle of least privilege rigorously to reduce the number of users with high privileges on local machines. 5. Segment networks to limit lateral movement opportunities if an attacker gains local access. 6. Maintain up-to-date backups and incident response plans to mitigate impact in case of exploitation. 7. Monitor official Microsoft security advisories for the release of patches or workarounds and apply them promptly once available. 8. Conduct regular vulnerability assessments focusing on legacy systems to identify and remediate similar risks proactively.