CVE-2025-53808 is a type confusion vulnerability (CWE-843) found in the Windows Defender Firewall Service on Microsoft Windows 10 Version 1809 (build 10.0.17763.0). Type confusion occurs when a program accesses a resource using an incompatible data type, leading to unpredictable behavior. In this case, the flaw allows an authorized local attacker to exploit the Windows Defender Firewall Service to elevate their privileges. The vulnerability requires local access and high privileges (PR:H), but no user interaction is needed (UI:N). The attacker can leverage this flaw to gain higher system privileges, potentially allowing full control over the affected system. The CVSS v3.1 base score is 6.7, categorized as medium severity, reflecting the combination of high impact on confidentiality, integrity, and availability (all rated high), but limited by the need for local access and existing elevated privileges. No known exploits are currently reported in the wild, and no patches or mitigation links have been published yet. The vulnerability was reserved in July 2025 and published in September 2025, indicating it is a recent discovery. The affected component, Windows Defender Firewall Service, is a critical system service responsible for managing firewall rules and network traffic filtering, making exploitation potentially impactful for system security and network protection.

For European organizations, this vulnerability poses a significant risk primarily in environments where Windows 10 Version 1809 is still in use, particularly in legacy systems or specialized industrial and enterprise setups. Successful exploitation could allow attackers with local access to escalate privileges, bypass security controls, and execute arbitrary code with elevated rights. This could lead to unauthorized access to sensitive data, disruption of firewall protections, and potential lateral movement within corporate networks. Given the critical role of the firewall service in network security, exploitation could undermine perimeter defenses, increasing exposure to further attacks. Organizations in sectors with stringent data protection requirements, such as finance, healthcare, and government, could face compliance risks and operational disruptions. Although the vulnerability requires local access and existing elevated privileges, insider threats or attackers who have compromised lower-privileged accounts could leverage this flaw to deepen their foothold. The absence of known exploits currently reduces immediate risk but does not eliminate the threat, especially as attackers may develop exploits once patches become available or if the vulnerability is reverse-engineered.

European organizations should prioritize identifying and inventorying systems running Windows 10 Version 1809 to assess exposure. Since no official patches are currently available, organizations should implement compensating controls such as restricting local administrative access strictly to trusted personnel, employing robust endpoint detection and response (EDR) solutions to monitor for suspicious privilege escalation attempts, and enforcing the principle of least privilege to minimize the number of accounts with elevated rights. Network segmentation can limit the impact of compromised hosts. Additionally, organizations should prepare for rapid deployment of patches once Microsoft releases updates by establishing a tested patch management process. Regularly auditing firewall configurations and monitoring Windows Defender Firewall Service logs can help detect anomalies indicative of exploitation attempts. User training to prevent unauthorized local access and maintaining up-to-date backups are also recommended to mitigate potential damage.