CVE-2025-47991 is a high-severity use-after-free vulnerability (CWE-416) identified in the Microsoft Input Method Editor (IME) component of Windows 10 Version 1809 (build 10.0.17763.0). The vulnerability arises when the IME improperly manages memory, leading to a use-after-free condition. This flaw can be exploited by an authorized local attacker to elevate privileges on the affected system. Specifically, the attacker must have some level of local access with limited privileges (PR:L) and can leverage this vulnerability to gain higher privileges without requiring user interaction (UI:N). The vulnerability impacts confidentiality, integrity, and availability (all rated high), and the scope is changed (S:C), meaning the exploit can affect resources beyond the initially compromised component. The attack complexity is high (AC:H), indicating exploitation requires specialized conditions or knowledge. No known exploits are currently in the wild, and no patches have been linked yet, though the vulnerability is publicly disclosed as of July 8, 2025. The vulnerability is significant because the IME is a core component used for input processing, and privilege escalation can lead to full system compromise if combined with other attack vectors.

For European organizations, this vulnerability poses a substantial risk, especially for enterprises and government agencies still operating legacy Windows 10 Version 1809 systems. Successful exploitation allows attackers with limited local access—such as through compromised user accounts, insider threats, or physical access—to escalate privileges to SYSTEM or administrative levels. This could lead to unauthorized access to sensitive data, disruption of critical services, and deployment of persistent malware or ransomware. The high impact on confidentiality, integrity, and availability means that data breaches, system tampering, and denial of service are plausible consequences. Given that many European organizations have phased out older Windows versions, the impact is mitigated for those fully updated; however, sectors with slower patch cycles or legacy dependencies remain vulnerable. Additionally, the lack of known exploits in the wild currently reduces immediate risk but does not eliminate the threat of future exploitation, especially as threat actors develop proof-of-concept code.

European organizations should prioritize the following specific actions: 1) Identify and inventory all systems running Windows 10 Version 1809, focusing on critical infrastructure and high-value targets. 2) Apply any official patches or security updates from Microsoft as soon as they become available; if no patch is yet released, monitor Microsoft advisories closely. 3) Implement strict local access controls and limit administrative privileges to reduce the attack surface. 4) Employ application whitelisting and endpoint detection and response (EDR) solutions to detect anomalous privilege escalation attempts. 5) Disable or restrict the use of the IME component where feasible, especially on systems that do not require complex input methods. 6) Conduct user awareness training to prevent unauthorized local access and reinforce physical security controls. 7) Regularly audit and monitor logs for suspicious activity indicative of privilege escalation attempts. These targeted measures go beyond generic advice by focusing on legacy system identification, IME-specific controls, and proactive monitoring.