Microsoft Security Advisory CVE-2025-21171 | .NET Remote Code Execution Vulnerability # Microsoft Security Advisory CVE-2025-21171 | .NET Remote Code Execution Vulnerability ## Executive summary Microsoft is releasing this security advisory to provide information about a vulnerability in .NET 9.0. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability. An attacker could exploit this vulnerability by sending a specially crafted request to the vulnerable web server. ## Announcement Announcement for this issue can be found at https://github.com/dotnet/runtime/issues/111423 ## Mitigation factors Microsoft has not identified any mitigating factors for this vulnerability. ## Affected software * Any .NET 9.0 application running on .NET 9.0.0 or earlier. ## Affected Packages The vulnerability affects any Microsoft .NET project if it uses any of affected packages versions listed below ### .NET 9 Package name | Affected version | Patched version ------------ | ---------------- | ------------------------- [Microsoft.NetCore.App.Runtime.linux-arm](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-arm) | >= 9.0.0, < 9.0.1 | 9.0.1 [Microsoft.NetCore.App.Runtime.linux-arm64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-arm64) | >= 9.0.0, < 9.0.1 | 9.0.1 [Microsoft.NetCore.App.Runtime.linux-musl-arm](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-musl-arm) | >= 9.0.0, < 9.0.1 | 9.0.1 [Microsoft.NetCore.App.Runtime.linux-musl-arm64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-musl-arm64) | >= 9.0.0, < 9.0.1 | 9.0.1 [Microsoft.NetCore.App.Runtime.linux-musl-x64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-musl-x64) | >= 9.0.0, < 9.0.1 | 9.0.1 [Microsoft.NetCore.App.Runtime.linux-x64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-x64) | >= 9.0.0, < 9.0.1 | 9.0.1 [Microsoft.NetCore.App.Runtime.osx-arm64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.osx-arm64) | >= 9.0.0, < 9.0.1 | 9.0.1 [Microsoft.NetCore.App.Runtime.osx-x64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.osx-x64) | >= 9.0.0, < 9.0.1 | 9.0.1 [Microsoft.NetCore.App.Runtime.win-arm](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.win-arm) | >= 9.0.0, < 9.0.1 | 9.0.1 [Microsoft.NetCore.App.Runtime.win-arm64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.win-arm64) | >= 9.0.0, < 9.0.1 | 9.0.1 [Microsoft.NetCore.App.Runtime.win-x64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.win-x64) | >= 9.0.0, < 9.0.1 | 9.0.1 [Microsoft.NetCore.App.Runtime.win-x86](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.win-x86) | >= 9.0.0, < 9.0.1 | 9.0.1 ## Advisory FAQ ### How do I know if I am affected? If you have a runtime or SDK with a version listed, or an affected package listed in [affected software](#affected-packages) or [affected packages](#affected-software), you're exposed to the vulnerability. ### How do I fix the issue? 1. To fix the issue please install the latest version of .NET 9.0. If you have installed one or more .NET SDKs through Visual Studio, Visual Studio will prompt you to update Visual Studio, which will also update your .NET SDKs. 2. If your application references the vulnerable package, update the package reference to the patched version. * You can list the versions you have installed by running the `dotnet --info` command. You will see output like the following; ``` .NET SDK: Version: 9.0.100 Commit: 59db016f11 Workload version: 9.0.100-manifests.3068a692 MSBuild version: 17.12.7+5b8665660 Runtime Environment: OS Name: Mac OS X OS Version: 15.2 OS Platform: Darwin RID: osx-arm64 Base Path: /usr/local/share/dotnet/sdk/9.0.100/ .NET workloads installed: There are no installed workloads to display. Configured to use loose manifests when installing new manifests. Host: Version: 9.0.0 Architecture: arm64 Commit: 9d5a6a9aa4 .NET SDKs installed: 9.0.100 [/usr/local/share/dotnet/sdk] .NET runtimes installed: Microsoft.AspNetCore.App 9.0.0 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App] Microsoft.NETCore.App 9.0.0 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App] Other architectures found: x64 [/usr/local/share/dotnet] registered at [/etc/dotnet/install_location_x64] Environment variables: Not set global.json file: Not found Learn more: https://aka.ms/dotnet/info Download .NET: https://aka.ms/dotnet/download ``` * If you're using .NET 9.0, you should download and install .NET 9.0 Runtime or .NET 9.0.100 SDK (for Visual Studio 2022 v17.12 latest Preview) from https://dotnet.microsoft.com/download/dotnet-core/9.0. Once you have installed the updated runtime or SDK, restart your apps for the update to take effect. Additionally, if you've deployed [self-contained applications](https://docs.microsoft.com/dotnet/core/deploying/#self-contained-deployments-scd) targeting any of the impacted versions, these applications are also vulnerable and must be recompiled and redeployed. ## Other Information ### Reporting Security Issues If you have found a potential security issue in .NET 9.0 please email details to secure@microsoft.com. Reports may qualify for the Microsoft .NET Core & .NET 5 Bounty. Details of the Microsoft .NET Bounty Program including terms and conditions are at . ### Support You can ask questions about this issue on GitHub in the .NET GitHub organization. The main repos are located at https://github.com/dotnet/runtime. The Announcements repo (https://github.com/dotnet/Announcements) will contain this bulletin as an issue and will include a link to a discussion issue. You can ask questions in the linked discussion issue. ### Disclaimer The information provided in this advisory is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply. ### External Links [CVE-2025-21171]( https://www.cve.org/CVERecord?id=CVE-2025-21171) ### Revisions V1.0 (January 14, 2024): Advisory published.