CVE-2025-26645 is a high-severity vulnerability classified as a relative path traversal (CWE-23) affecting the Microsoft Windows App Client for Windows Desktop, specifically version 1.00. This vulnerability allows an unauthorized attacker to execute arbitrary code remotely over a network without requiring privileges, although user interaction is necessary. The flaw arises from improper validation of file paths within the Remote Desktop Client component, enabling attackers to manipulate file paths to access or execute files outside the intended directory structure. Exploiting this vulnerability could allow an attacker to execute malicious code with the privileges of the user running the application, potentially leading to full system compromise. The CVSS v3.1 base score is 8.8, indicating a high impact on confidentiality, integrity, and availability. The attack vector is network-based with low complexity and no privileges required, but user interaction is necessary, which slightly reduces the ease of exploitation. No known exploits are currently reported in the wild, and no patches have been linked yet, suggesting that organizations should prioritize monitoring and mitigation efforts. The vulnerability is particularly critical because Remote Desktop Client is widely used for remote access and management, making it an attractive target for attackers seeking to gain unauthorized access or persist within enterprise environments.

For European organizations, this vulnerability poses a significant risk due to the widespread use of Microsoft Windows and Remote Desktop technologies in corporate, governmental, and critical infrastructure sectors. Successful exploitation could lead to unauthorized code execution, data breaches, ransomware deployment, or lateral movement within networks. Confidentiality could be compromised by unauthorized access to sensitive data, integrity could be undermined by malicious code altering system files or configurations, and availability could be affected through denial-of-service or ransomware attacks. The requirement for user interaction may limit mass exploitation but targeted phishing or social engineering campaigns could facilitate attacks. Given the critical role of remote desktop services in enabling remote work and system administration, disruption or compromise could have severe operational and reputational consequences for European entities.

European organizations should implement a multi-layered mitigation strategy: 1) Immediately monitor for unusual Remote Desktop Client activity and network traffic anomalies that could indicate exploitation attempts. 2) Restrict Remote Desktop access using network segmentation, VPNs, and strict firewall rules to limit exposure to untrusted networks. 3) Educate users about the risks of interacting with unsolicited remote desktop connection requests or files to reduce the likelihood of successful social engineering. 4) Employ application whitelisting and endpoint protection solutions capable of detecting and blocking unauthorized code execution. 5) Regularly audit and update Remote Desktop Client software and related components, applying patches promptly once available from Microsoft. 6) Implement robust logging and incident response procedures to quickly identify and contain any exploitation attempts. 7) Consider disabling or limiting Remote Desktop Client functionality where not essential to reduce the attack surface.