CVE-2025-26646
📋 TL;DR
This vulnerability allows an authorized attacker to control file names or paths in .NET, Visual Studio, and Build Tools for Visual Studio, enabling network-based spoofing attacks. It affects systems running vulnerable versions of these Microsoft development tools. Attackers must have some level of authorization to exploit this weakness.
💻 Affected Systems
- .NET
- Visual Studio
- Build Tools for Visual Studio
📦 What is this software?
.net by Microsoft
.net by Microsoft
Build Tools by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
An attacker could redirect file operations to malicious locations, potentially leading to code execution, data theft, or system compromise through spoofed components.
Likely Case
Attackers could manipulate build processes or application behavior by substituting legitimate files with malicious ones, leading to supply chain attacks or application manipulation.
If Mitigated
With proper access controls and network segmentation, impact is limited to isolated development environments with minimal production exposure.
🎯 Exploit Status
Exploitation requires authorized access and knowledge of the target environment's file structure and processes.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Microsoft Update Guide for specific patched versions
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-26646
Restart Required: Yes
Instructions:
1. Visit the Microsoft Update Guide link. 2. Identify affected products in your environment. 3. Apply the latest security updates from Windows Update or Microsoft Update Catalog. 4. Restart affected systems as required.
🔧 Temporary Workarounds
Restrict network access to development tools
windowsLimit network connectivity to Visual Studio and Build Tools to trusted networks only
Use Windows Firewall: New-NetFirewallRule -DisplayName 'Block VS Network' -Direction Inbound -Program 'C:\Program Files\Microsoft Visual Studio\...\devenv.exe' -Action Block
Implement strict file access controls
windowsApply least privilege principles to file system permissions for development directories
icacls "C:\Program Files\Microsoft Visual Studio" /inheritance:r /grant:r "BUILTIN\Administrators:(OI)(CI)F" /grant:r "NT AUTHORITY\SYSTEM:(OI)(CI)F"
🧯 If You Can't Patch
- Isolate development environments from production networks and internet access
- Implement application allowlisting to prevent unauthorized processes from interacting with development tools
🔍 How to Verify
Check if Vulnerable:
Check installed versions of .NET, Visual Studio, and Build Tools against Microsoft's advisory for vulnerable versionsCheck Version:
For .NET: dotnet --version; For Visual Studio: Check Help > About Microsoft Visual StudioVerify Fix Applied:
Verify that patched versions are installed and no vulnerable versions remain📡 Detection & Monitoring
Log Indicators:
- Unusual file access patterns in development directories
- Unexpected network connections from development tools
- Failed file operations with suspicious paths
Network Indicators:
- Network traffic to/from development tools on non-standard ports
- Suspicious file transfer patterns involving build artifacts
SIEM Query:
source="windows_security" EventID=4663 ObjectType="File" ObjectName="*visualstudio*" OR ObjectName="*.sln" OR ObjectName="*.csproj" | stats count by user, ObjectName