CVE-2026-70165 in .NET
Summary
by MITRE • 10/14/2026
Improper link resolution before file access ('link following') in .NET allows an authorized attacker to elevate privileges locally.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 10/14/2026
The vulnerability described constitutes a classic Time-of-Check-to-Time-of-Use (TOCTOU) race condition rooted in improper handling of symbolic links or hard links within the Microsoft .NET framework environment. This specific flaw, often categorized under CWE-59 Improper Link Resolution Before File Access, occurs when an application performs security checks on a file path before actually accessing it, but fails to ensure that the resource identified by that path remains unchanged during the interval between the check and the access operation. In this context, an attacker who possesses valid local authentication credentials can exploit this window of opportunity to manipulate the filesystem structure dynamically. By replacing or redirecting the target link after the initial validation but before the actual file read or write operation occurs, the attacker forces the .NET runtime to interact with a different resource than originally intended by the security logic.
From an operational perspective, this vulnerability allows for local privilege escalation because the application likely relies on path-based permissions that do not account for such dynamic redirections. For instance, if a service running under high-privilege accounts reads configuration files or sensitive data from user-writable directories without validating link integrity at the moment of access, an attacker can point those links to critical system files. This enables the unauthorized reading of confidential information or, more critically, the modification of system-critical configurations that dictate application behavior. The impact is severe as it bypasses standard operating system permission models by exploiting the logical gap in the application's file handling routine rather than breaking cryptographic protections or network boundaries directly.
This type of vulnerability aligns with MITRE ATT&CK technique T1059 Command and Scripting Interpreter, specifically when used to facilitate further exploitation steps such as script injection via modified configuration files, and relates closely to T1222 File and Directory Permissions Modification if the attacker modifies permissions on linked targets. It also reflects CWE-367 TOCTOU Race Condition, highlighting the fundamental design flaw where state changes are not atomic with respect to security checks. The root cause is typically a failure to use secure file access APIs that validate link integrity at the time of opening, such as using specific flags like O_NOFOLLOW on Unix-like systems or equivalent secure handle creation methods in Windows environments that prevent following links unless explicitly intended and verified atomically.
Mitigation strategies must focus on eliminating the race condition by ensuring atomic operations during file access. Developers should refactor code to use APIs that open files with options that disable link following, thereby forcing direct interaction with the inode or file record rather than its symbolic target. Additionally implementing strict input validation for all file paths and avoiding reliance on predictable directory structures where users have write permissions is essential. Applying vendor-provided patches that update the .NET runtime's internal file handling logic to enforce stricter security checks at the point of access, not just before it, is the primary remediation path. System administrators should also monitor for unusual symlink creation activities in directories accessed by privileged services as a defensive measure against active exploitation attempts.