CVE-2025-26646 is a high-severity vulnerability identified in Microsoft .NET 8.0, specifically categorized under CWE-73: External Control of File Name or Path. This vulnerability arises when an attacker with authorized access can externally influence file names or paths used by the .NET runtime, Visual Studio, or Build Tools for Visual Studio. By manipulating these file paths, the attacker can perform spoofing attacks over a network, potentially redirecting file operations to malicious or unintended locations. The vulnerability requires low attack complexity and privileges (PR:L), but does require user interaction (UI:R). The scope is unchanged (S:U), meaning the impact is confined to the vulnerable component. The CVSS 3.1 base score is 8.0, reflecting high impact on confidentiality, integrity, and availability (C:H/I:H/A:H). The vulnerability can lead to unauthorized disclosure, modification, or deletion of files, which could compromise application behavior, leak sensitive data, or disrupt services. Although no known exploits are currently in the wild, the presence of this vulnerability in a widely used development framework and tools indicates a significant risk, especially in environments where .NET 8.0 is deployed. The lack of available patches at the time of publication increases the urgency for mitigation.

For European organizations, this vulnerability poses a substantial risk due to the widespread adoption of Microsoft .NET technologies in enterprise applications, government systems, and critical infrastructure. Exploitation could lead to data breaches involving personal data protected under GDPR, resulting in regulatory penalties and reputational damage. The ability to spoof file paths may allow attackers to inject malicious code or manipulate application logic, potentially disrupting business operations or enabling further lateral movement within networks. Organizations relying on Visual Studio and Build Tools for software development and deployment may face compromised build processes, risking the integrity of software supply chains. The high impact on confidentiality, integrity, and availability underscores the threat to sensitive sectors such as finance, healthcare, and public administration across Europe.

European organizations should implement immediate compensating controls while awaiting official patches. These include: 1) Restricting access to .NET 8.0 environments and build tools to trusted personnel only, minimizing the risk of authorized attacker exploitation. 2) Implementing strict input validation and sanitization on any user-controllable file path inputs within applications using .NET 8.0 to prevent path manipulation. 3) Employing application whitelisting and file integrity monitoring to detect unauthorized changes to critical files or build artifacts. 4) Utilizing network segmentation to isolate development and build environments from production and sensitive data stores. 5) Monitoring logs for unusual file access patterns or spoofing attempts indicative of exploitation. 6) Preparing for rapid patch deployment once Microsoft releases updates by establishing robust patch management processes. Additionally, conducting security code reviews and penetration testing focused on file path handling can help identify and remediate vulnerable code paths.