CVE-2025-21173

Overview

.NET is a free, open-source, cross-platform framework for building modern apps and powerful cloud services. It consists of a runtime and a developer platform SDK made up of tools, programming languages, and libraries for building many different types of applications. 

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A vulnerability (CVE-2025-21173) exists in the .NET SDK as a result of insecure temp file usage on Linux that allows local system privilege escalation by attackers. 

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Per CWE-379: Creation of Temporary File in Directory with Insecure Permissions, is when a product creates a temporary file in a directory whose permissions allow unintended actors to determine the file's existence or otherwise access that file.

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This issue affects Linux installations of .NET.

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Additionally, if you've deployed self-contained applications targeting any of the impacted versions, these applications are also vulnerable and must be recompiled and redeployed.

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Details

Module Info

• Product: 

• Any .NET 6.0 application running on Linux installations of .NET 6.0.36 or earlier.
• Any .NET 8.0 application running on Linux installations of .NET 8.0.11 or earlier.
• Any .NET 9.0 application running on Linux installations of .NET 9.0.0 or earlier.

• Affected packages: 
  
  • Microsoft.NetCore.App.Runtime.linux-arm
  • Microsoft.NetCore.App.Runtime.linux-arm64
  • Microsoft.NetCore.App.Runtime.linux-musl-arm
  • Microsoft.NetCore.App.Runtime.linux-musl-arm64
  • Microsoft.NetCore.App.Runtime.linux-musl-x64
  • Microsoft.NetCore.App.Runtime.linux-x64
• Affected versions: 
  
  • >= 6.0.0 <= 6.0.36
  • >= 8.0.0 <= 8.0.11
  • <= 9.0.0
• GitHub repository: https://github.com/dotnet/sdk   
• Published packages: Download .NET (Linux, macOS, and Windows)
• Package manager: 
  
  • Nuget
  • Windows Installer
  • Docker
• Fixed in: .NET - Never-Ending Support (NES) | HeroDevs v6.1.0

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Vulnerability Info

This High-severity vulnerability is found in the .NET SDK. This only affects .NET on Linux operating systems. An attacker could exploit this vulnerability by writing a specially crafted file in the security context of the local system.

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Mitigation

.NET 6.x is End-of-Life and will not receive any updates to address this issue. For more information see .NET and .NET Core official support policy.

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Users of the affected components should apply one of the following mitigations:

• Upgrade affected applications to one of:
  
  • .NET >= 8.0.12
  • .NET >= 9.0.1
• Leverage a commercial support partner like HeroDevs for post-EOL security support.

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Credits

• Daniel Plaisted with Microsoft
• Noah Gilson with Microsoft