CVE-2025-21173: Visual Studio 2022 Privilege Escalation

CVE-2025-21173 Overview

CVE-2025-21173 is a .NET Elevation of Privilege vulnerability affecting Microsoft Visual Studio 2022 and .NET runtime versions 8.0.0 and 9.0.0 on Linux systems. This vulnerability is classified under CWE-379 (Creation of Temporary File in Directory with Insecure Permissions), which allows local attackers with limited privileges to escalate their access through improper handling of temporary files.

The vulnerability requires local access and user interaction, but once exploited, can lead to complete compromise of confidentiality, integrity, and availability on the affected system.

Critical Impact

Local attackers with low privileges can exploit insecure temporary file handling in .NET to gain elevated privileges, potentially compromising sensitive data and system integrity.

Affected Products

• Microsoft Visual Studio 2022
• Microsoft .NET 8.0.0
• Microsoft .NET 9.0.0 (on Linux)

Discovery Timeline

• January 14, 2025 - CVE-2025-21173 published to NVD
• May 6, 2025 - Last updated in NVD database

Technical Details for CVE-2025-21173

Vulnerability Analysis

This elevation of privilege vulnerability stems from how .NET creates and manages temporary files on Linux systems. The weakness relates to CWE-379, which describes scenarios where an application creates temporary files in directories that have insecure permissions. When a privileged process creates temporary files in such locations without proper access controls, a local attacker can manipulate these files to gain elevated privileges.

The vulnerability affects .NET applications running on Linux when using Visual Studio 2022 for development. The local attack vector means an attacker must have some level of access to the target system, but the low privilege requirement indicates that even standard user accounts can potentially exploit this flaw.

Root Cause

The root cause is the creation of temporary files in directories with insecure permissions (CWE-379). When .NET runtime components on Linux create temporary files without enforcing restrictive permissions, race conditions can occur where an attacker substitutes or modifies these files before the legitimate process accesses them. This can lead to privilege escalation if the original process runs with elevated privileges or handles sensitive operations.

Attack Vector

The attack requires local access to the target system with low-privilege credentials. The attacker exploits the window of opportunity between when the .NET application creates a temporary file and when it uses that file. By placing malicious content or symbolic links in predictable temporary file locations, the attacker can trick the application into executing code or accessing files with elevated privileges.

The exploitation scenario typically involves:

1. Identifying the predictable temporary file location used by .NET
2. Monitoring for file creation events
3. Racing to replace or manipulate the temporary file
4. Causing the vulnerable application to process the malicious content with elevated privileges

Detection Methods for CVE-2025-21173

Indicators of Compromise

• Unusual file operations in /tmp or other temporary directories involving .NET processes
• Symbolic link creation attempts targeting temporary files created by .NET applications
• Unexpected privilege escalation events associated with dotnet or Visual Studio processes
• File permission anomalies in temporary directories used by .NET runtime

Detection Strategies

• Monitor file system events in temporary directories for suspicious race condition patterns
• Implement audit logging for privilege escalation attempts on systems running .NET applications
• Use SentinelOne's behavioral AI to detect anomalous process privilege changes
• Review .NET application logs for unusual file access errors or permission denied messages

Monitoring Recommendations

• Enable detailed auditing on Linux systems for file creation in /tmp and application-specific temp directories
• Configure alerts for unexpected privilege escalation events involving .NET runtime processes
• Deploy endpoint detection solutions capable of identifying TOCTOU (Time-of-Check Time-of-Use) attack patterns
• Monitor for symbolic link creation activity targeting .NET temporary file paths

How to Mitigate CVE-2025-21173

Immediate Actions Required

• Apply Microsoft security updates for .NET 8.0 and 9.0 as outlined in the Microsoft Security Update Guide
• Update Visual Studio 2022 to the latest patched version
• Review and restrict permissions on temporary directories used by .NET applications
• Audit systems for signs of exploitation attempts

Patch Information

Microsoft has released security updates to address this vulnerability. Administrators should consult the Microsoft Security Update Guide for specific patch details and installation instructions. The patches ensure that .NET creates temporary files with appropriate restrictive permissions, eliminating the race condition window.

Workarounds

• Configure dedicated temporary directories with restricted permissions for .NET applications
• Use Linux-specific security controls like mount options (noexec, nosuid) on temporary filesystems
• Implement application-level sandboxing to limit the impact of potential privilege escalation
• Consider containerizing .NET applications to isolate them from the host filesystem

# Harden temporary directory permissions for .NET applications
chmod 700 /var/tmp/dotnet
chown root:root /var/tmp/dotnet

# Mount /tmp with security options (in /etc/fstab)
# tmpfs /tmp tmpfs defaults,noexec,nosuid,nodev 0 0