CVE-2025-54104 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, a critical component responsible for managing network traffic filtering and security policies on the host. The vulnerability allows an authorized local attacker—meaning the attacker must have some level of legitimate access to the system—to exploit a type confusion error to elevate their privileges. Type confusion vulnerabilities occur when a program accesses a resource or object assuming it is of one type, but it is actually of another incompatible type, leading to undefined behavior that attackers can leverage to execute arbitrary code or escalate privileges. In this case, the attacker can gain higher privileges than initially granted, potentially reaching SYSTEM-level access. The CVSS v3.1 base score is 6.7 (medium severity), reflecting that the attack vector is local (AV:L), requires low attack complexity (AC:L), and high privileges (PR:H), with no user interaction (UI:N). The impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H), indicating that successful exploitation could lead to full system compromise. No known exploits are currently reported in the wild, and no patches or mitigations have been linked yet. The vulnerability was published on September 9, 2025, with the reservation date on July 16, 2025. Given the affected product is Windows 10 Version 1809, which is an older Windows 10 release, organizations still running this version are at risk. The Windows Defender Firewall Service is a core security component, so exploitation could undermine the host's security posture significantly.

For European organizations, this vulnerability poses a significant risk especially to those still operating legacy Windows 10 Version 1809 systems, which may be common in environments with slower upgrade cycles such as industrial control systems, government agencies, or enterprises with strict change management policies. Successful exploitation can lead to local privilege escalation, allowing attackers who have already gained limited access (e.g., via phishing, insider threat, or other means) to gain full control over affected machines. This can facilitate lateral movement, deployment of ransomware, data exfiltration, or sabotage. The high impact on confidentiality, integrity, and availability means sensitive data could be compromised, system configurations altered, or critical services disrupted. Since the vulnerability affects the Windows Defender Firewall Service, it could also weaken network defenses, potentially allowing further network-based attacks. European organizations subject to strict data protection regulations like GDPR could face compliance risks and financial penalties if breaches occur due to this vulnerability. The lack of known exploits in the wild currently reduces immediate risk but does not eliminate it, as attackers may develop exploits over time.

1. Immediate mitigation should focus on upgrading affected systems to a supported and patched version of Windows 10 or later, as Windows 10 Version 1809 is out of mainstream support and unlikely to receive security updates. 2. If upgrading is not immediately feasible, organizations should implement strict access controls to limit local user privileges, ensuring that only trusted users have local access to vulnerable systems. 3. Employ application whitelisting and endpoint detection and response (EDR) solutions to monitor and block suspicious activities indicative of privilege escalation attempts. 4. Regularly audit and harden firewall configurations and Windows Defender settings to minimize attack surface. 5. Use network segmentation to isolate legacy systems and reduce the risk of lateral movement. 6. Monitor system logs and security alerts for unusual behavior related to the Windows Defender Firewall Service. 7. Prepare incident response plans specifically addressing local privilege escalation scenarios. 8. Stay updated with Microsoft security advisories for any forthcoming patches or workarounds related to this CVE.