CVE-2025-29966 is a high-severity heap-based buffer overflow vulnerability identified in the Microsoft Windows App Client for Windows Desktop, specifically version 1.00. This vulnerability is classified under CWE-122, indicating that improper handling of memory buffers on the heap can lead to memory corruption. The flaw exists in the Windows Remote Desktop component, which allows remote network access to Windows desktops. An unauthorized attacker can exploit this vulnerability over the network without requiring prior authentication, though user interaction is needed (as indicated by the CVSS vector UI:R). Successful exploitation enables the attacker to execute arbitrary code remotely with high impact on confidentiality, integrity, and availability. The vulnerability has a CVSS v3.1 base score of 8.8, reflecting its critical nature due to ease of network exploitation (AV:N), low attack complexity (AC:L), no privileges required (PR:N), and the potential for complete system compromise (C:H/I:H/A:H). Although no public exploits are known in the wild yet, the vulnerability’s characteristics make it a significant risk, especially in environments where Windows Remote Desktop is exposed to untrusted networks. The lack of available patches at the time of disclosure increases the urgency for mitigation and monitoring. Given the widespread use of Windows in enterprise environments, this vulnerability poses a serious threat to organizations relying on Remote Desktop services for remote access and management.

For European organizations, the impact of CVE-2025-29966 can be substantial. Many enterprises, government agencies, and critical infrastructure operators in Europe use Windows Remote Desktop for remote administration and teleworking, especially post-pandemic where remote work is prevalent. Exploitation could lead to unauthorized access to sensitive data, disruption of business operations, and potential lateral movement within networks. The confidentiality breach could expose personal data protected under GDPR, leading to regulatory penalties and reputational damage. Integrity and availability impacts could disrupt critical services, including financial systems, healthcare, and public administration. The fact that exploitation does not require authentication increases the risk of widespread attacks, including ransomware deployment or espionage campaigns targeting European entities. The absence of known exploits currently provides a window for proactive defense, but the high CVSS score and network attack vector suggest attackers may develop exploits rapidly.

Specific mitigation steps for European organizations include: 1) Immediate review and restriction of Remote Desktop exposure to the internet by implementing network-level firewalls and VPNs to limit access only to trusted users and networks. 2) Employ multi-factor authentication (MFA) on all Remote Desktop access points to add an additional security layer despite the vulnerability not requiring authentication. 3) Monitor network traffic for unusual Remote Desktop connection attempts and anomalous behavior indicative of exploitation attempts. 4) Apply strict endpoint protection and behavior-based detection tools that can identify exploitation attempts targeting heap overflows. 5) Disable or uninstall the Windows App Client for Windows Desktop version 1.00 if it is not essential, or isolate it in segmented network zones. 6) Stay alert for official patches or updates from Microsoft and plan for rapid deployment once available. 7) Conduct internal security awareness training to reduce risky user interactions that might trigger exploitation. 8) Implement robust backup and recovery procedures to mitigate potential ransomware or data loss scenarios resulting from exploitation.