CVE-2025-55340 is a vulnerability categorized under CWE-287 (Improper Authentication) affecting Microsoft Windows 11 Version 25H2 (build 10.0.26200.0). The flaw resides in the Windows Remote Desktop Protocol (RDP) implementation, where an authorized attacker with low privileges on the local system can bypass authentication controls designed to protect RDP sessions or related security features. This bypass does not require user interaction, increasing the risk of automated or stealthy exploitation. The vulnerability has a CVSS 3.1 base score of 7.0, reflecting high severity with a local attack vector (AV:L), high attack complexity (AC:H), low privileges required (PR:L), and no user interaction (UI:N). The impact includes full compromise of confidentiality, integrity, and availability (C:H/I:H/A:H), meaning an attacker could potentially gain unauthorized access to sensitive information, alter system configurations, or disrupt services. The scope is unchanged (S:U), indicating the vulnerability affects only the vulnerable component without extending to other system components. No known exploits have been reported in the wild as of the publication date (October 14, 2025), but the vulnerability was reserved in August 2025, suggesting recent discovery. The lack of available patches at the time of reporting necessitates proactive risk management. The vulnerability is particularly concerning for environments relying on RDP for remote administration or user access, as it undermines the authentication mechanisms that protect these sessions from unauthorized local users.

For European organizations, the impact of CVE-2025-55340 can be significant, especially in sectors with high reliance on Windows 11 and RDP for remote work, such as finance, government, healthcare, and critical infrastructure. Exploitation could lead to unauthorized access to sensitive data, disruption of business operations, and potential lateral movement within networks. The ability of a low-privileged local attacker to bypass authentication controls increases insider threat risks and the potential for malware or ransomware deployment. Confidentiality breaches could expose personal data protected under GDPR, leading to regulatory penalties and reputational damage. Integrity violations could compromise system configurations and data accuracy, while availability impacts could disrupt critical services. The absence of known exploits currently provides a window for mitigation, but the high severity score underscores the urgency for European organizations to assess and remediate this vulnerability promptly to avoid operational and compliance risks.

1. Monitor Microsoft security advisories closely and apply official patches immediately upon release to remediate the vulnerability. 2. Restrict local access to systems running Windows 11 Version 25H2, especially those providing RDP services, to trusted personnel only. 3. Implement strict access controls and auditing on RDP usage to detect unauthorized attempts or anomalous behavior. 4. Employ endpoint detection and response (EDR) solutions to identify potential exploitation attempts or privilege escalation activities locally. 5. Consider disabling RDP on systems where it is not strictly necessary or use alternative secure remote access methods with multi-factor authentication. 6. Harden local user accounts by enforcing least privilege principles and regularly reviewing user permissions. 7. Conduct security awareness training to inform administrators and users about the risks of local privilege misuse and the importance of physical and logical access controls. 8. Prepare incident response plans that include scenarios involving local privilege escalation and RDP-related attacks. 9. Use network segmentation to limit the spread of potential compromises originating from exploited systems. 10. Regularly update and patch all software components to reduce the attack surface and prevent exploitation of known vulnerabilities.