CVE-2025-26645 is a relative path traversal vulnerability identified in Microsoft Windows App Client for Windows Desktop version 1.00. This vulnerability arises from improper validation of file paths, allowing an attacker to manipulate relative paths to access or overwrite arbitrary files on the target system. Exploiting this flaw enables remote, unauthenticated attackers to execute arbitrary code over the network, potentially leading to full system compromise. The attack vector is network-based (AV:N), requires no privileges (PR:N), but does require user interaction (UI:R), such as convincing a user to connect to a malicious remote desktop server or open a crafted resource. The vulnerability affects confidentiality, integrity, and availability (all rated high), as attackers can execute code, access sensitive data, or disrupt system operations. Although no public exploits have been reported yet, the vulnerability is publicly disclosed and rated with a CVSS 3.1 score of 8.8, indicating a high risk. The vulnerability is categorized under CWE-23 (Relative Path Traversal), which typically involves bypassing file system restrictions to access unauthorized files, and CWE-284 (Improper Access Control), highlighting insufficient security checks. The lack of available patches at the time of disclosure increases the urgency for mitigation. This vulnerability is particularly concerning for environments relying on remote desktop technologies, as it can be exploited remotely without authentication, increasing the attack surface significantly.

For European organizations, the impact of CVE-2025-26645 is substantial. Many enterprises, government agencies, and critical infrastructure operators in Europe rely heavily on Microsoft Windows environments and remote desktop solutions for daily operations and remote work. Exploitation could lead to unauthorized access to sensitive data, disruption of business processes, and potential lateral movement within networks. Confidentiality breaches could expose personal data protected under GDPR, leading to regulatory penalties and reputational damage. Integrity and availability impacts could disrupt critical services, especially in sectors like finance, healthcare, and public administration. The requirement for user interaction somewhat limits automated exploitation but does not eliminate risk, as social engineering or phishing could facilitate attacks. The absence of known exploits currently provides a window for proactive defense, but the high CVSS score and network attack vector necessitate urgent attention to prevent future exploitation. Organizations with remote desktop clients exposed to untrusted networks are particularly vulnerable.

1. Monitor Microsoft security advisories closely and apply official patches immediately once released for Windows App Client for Windows Desktop version 1.00. 2. Until patches are available, restrict network access to remote desktop clients using network segmentation, firewalls, and VPNs to limit exposure to untrusted networks. 3. Implement strict file system permissions to minimize the impact of path traversal by limiting write and execute permissions on critical directories. 4. Educate users about the risks of connecting to untrusted remote desktop servers and implement multi-factor authentication to reduce the risk of social engineering exploitation. 5. Employ endpoint detection and response (EDR) solutions to monitor for suspicious file access patterns and anomalous process executions indicative of exploitation attempts. 6. Regularly audit remote desktop configurations and disable unnecessary features or protocols that could be leveraged in attacks. 7. Use application whitelisting to prevent unauthorized code execution resulting from exploitation. 8. Maintain comprehensive backups and incident response plans to recover quickly from potential compromises.