CVE-2025-55340 is a vulnerability classified under CWE-287 (Improper Authentication) found in Microsoft Windows 11 Version 25H2, specifically version 10.0.26200.0. The flaw resides in the Windows Remote Desktop Protocol (RDP) component, where an authorized attacker with local access and low privileges can bypass certain security features. This bypass does not require user interaction but does require the attacker to have some level of authenticated local access, making the attack vector local with high attack complexity. The vulnerability affects the confidentiality, integrity, and availability of the system by potentially allowing unauthorized access or privilege escalation through the RDP service. The CVSS v3.1 score is 7.0 (high), reflecting the significant impact but limited attack vector and complexity. No public exploits are known at this time, and no patches have been linked yet, though the vulnerability was published on October 14, 2025. The improper authentication issue could allow attackers to circumvent security controls designed to protect RDP sessions, potentially leading to unauthorized data access or system control. This vulnerability is particularly concerning for environments relying heavily on RDP for remote management or remote work scenarios.

For European organizations, this vulnerability poses a significant risk due to the widespread use of Windows 11 25H2 in enterprise environments and the common reliance on RDP for remote access and administration. Exploitation could lead to unauthorized access to sensitive corporate resources, data breaches, or disruption of critical services. The local access requirement limits remote exploitation but insider threats or compromised local accounts could leverage this flaw to escalate privileges or bypass security controls. This could impact confidentiality by exposing sensitive information, integrity by allowing unauthorized changes, and availability by disrupting remote access services. Organizations in sectors such as finance, government, healthcare, and critical infrastructure, which often use RDP for remote management, could face operational and reputational damage if exploited. The lack of known exploits provides a window for proactive mitigation, but the high severity score indicates that the threat should be taken seriously.

1. Apply official patches from Microsoft immediately once they become available to address CVE-2025-55340. 2. Until patches are released, restrict local access to systems running Windows 11 25H2, especially those exposing RDP services. 3. Implement strict access controls and monitoring on accounts with local access privileges to detect suspicious activities. 4. Use network segmentation to limit the exposure of RDP-enabled systems and reduce the attack surface. 5. Employ multi-factor authentication (MFA) for all remote access methods to add an additional security layer. 6. Regularly audit and review local user accounts and permissions to minimize the number of users with local access. 7. Monitor security logs for unusual RDP authentication attempts or bypass indicators. 8. Educate IT staff and users about the risks of local privilege misuse and enforce the principle of least privilege. 9. Consider disabling RDP on systems where it is not essential to reduce potential attack vectors. 10. Maintain up-to-date endpoint protection and intrusion detection systems to identify exploitation attempts early.