CVE-2026-69805 in Visual Studio
Summary
by MITRE • 09/09/2026
External control of file name or path in .NET allows an unauthorized attacker to elevate privileges over a network.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability described constitutes a critical security flaw within the Microsoft .NET framework, specifically categorized under External Control of File Name or Path. This type of issue arises when software constructs a file system path using input that is influenced by an external actor without sufficiently validating or sanitizing that input. In this specific instance, the attack vector is network-based, meaning an attacker can exploit this weakness remotely over a local area network or even across the internet if exposed services are present. The core technical flaw lies in the application's failure to properly constrain file paths derived from user-supplied data, allowing for path traversal sequences such as dot-dot-slash (.. /) characters to be injected into the request parameters.
When an attacker successfully injects these malicious path components, they can manipulate the intended destination of a file operation performed by the .NET application. This manipulation often leads to unauthorized access to sensitive files located outside the expected directory structure or allows for the creation and overwriting of arbitrary files within directories where the application process has write permissions. The severity of this vulnerability is significantly amplified because it facilitates privilege escalation. By controlling which files are read, written, or deleted, an attacker can potentially compromise configuration files, inject malicious code into executable locations, or overwrite critical system resources that dictate how the application behaves.
The operational impact of exploiting this flaw extends beyond simple data leakage. If the .NET application runs with elevated privileges, such as those associated with a service account or administrator rights on the host machine, the attacker inherits these permissions through the compromised process context. This allows for complete control over the underlying operating system. The attacker could install backdoors, modify authentication mechanisms to bypass security controls, or pivot further into other systems within the network infrastructure. In enterprise environments where .NET applications are frequently used as web services or API endpoints, this vulnerability represents a high-risk entry point that can lead to full system compromise and widespread data exfiltration.
From an industry standard perspective, this vulnerability aligns with CWE-22: Improper Limitation of a Pathname to a Restricted Directory, commonly known as path traversal. It also maps to the MITRE ATT&CK framework under techniques related to Command and Scripting Interpreter or File Manipulation, specifically T1059 if scripts are involved in the exploitation chain, or more broadly under Initial Access and Persistence tactics depending on how the attacker leverages the file system control for long-term access. The lack of input validation is a classic example of CWE-20: Improper Input Validation, which serves as the root cause enabling the path manipulation.
Mitigation strategies must focus on strict input validation and secure coding practices within the .NET environment. Developers should implement allow-listing techniques where only known safe characters or specific file names are accepted, rather than relying on block lists for dangerous patterns like ".. /". Additionally, using canonicalization functions provided by the framework to resolve paths before processing can help detect traversal attempts early in the request lifecycle. It is also crucial to enforce principle of least privilege by ensuring that .NET applications run with minimal necessary permissions, thereby limiting the potential damage even if an attacker succeeds in manipulating file operations. Regular security audits and static code analysis tools configured to detect path manipulation vulnerabilities are essential for maintaining a robust defense posture against this class of threats.