Microsoft Security Advisory CVE-2025-26646: .NET Spoofing Vulnerability
Executive summary
Microsoft is releasing this security advisory to provide information about a vulnerability in .NET 9.0.xxx and .NET 8.0.xxx SDK. This advisory also provides guidance on what developers can do to update their applications to address this vulnerability.
A vulnerability exists in .NET SDK or MSBuild applications where external control of file name or path allows an unauthorized attacked to perform spoofing over a network.
Discussion
Discussion for this issue can be found at dotnet/msbuild#11846
Mitigation factors
Projects which do not utilize the DownloadFile build task are not susceptible to this vulnerability.
Affected software
- Any installation of .NET 9.0.105 SDK, .NET 9.0.203 SDK or earlier.
- Any installation of .NET 8.0.115 SDK, .NET 8.0.311 SDK, .NET 8.0.408 SDK or earlier.
Affected Packages
The vulnerability affects any Microsoft .NET Core project if it uses any of affected packages versions listed below
| Package name |
Affected version |
Patched version |
| Microsoft.Build.Tasks.Core |
>= 15.8.166, <=15.9.20
>=16.0.461, <= 16.11.0
>= 17.0.0, <= 17.8.3
>= 17.9.5, <= 17.10.4
17.11.4
17.12.6
17.13.9 |
15.9.30
16.11.6
17.8.29
17.10.29
17.12.36
17.13.26
17.14.8 |
Advisory FAQ
How do I know if I am affected?
If you have a .NET SDK with a version listed, or an affected package listed in affected software or affected packages, you're exposed to the vulnerability.
How do I fix the issue?
- To fix the issue please install the latest version of .NET 9.0 SDK or .NET 8.0 SDK. 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.
- 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
Once you have installed the updated SDK, restart your apps for the update to take effect.
Other Information
Reporting Security Issues
If you have found a potential security issue in .NET 8.0 or .NET 9.0, please email details to [email protected]. Reports may qualify for the Microsoft .NET Core & .NET 5 Bounty. Details of the Microsoft .NET Bounty Program including terms and conditions are at https://aka.ms/corebounty.
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/aspnetcore. 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.
References
Microsoft Security Advisory CVE-2025-26646: .NET Spoofing Vulnerability
Executive summary
Microsoft is releasing this security advisory to provide information about a vulnerability in .NET 9.0.xxx and .NET 8.0.xxx SDK. This advisory also provides guidance on what developers can do to update their applications to address this vulnerability.
A vulnerability exists in .NET SDK or MSBuild applications where external control of file name or path allows an unauthorized attacked to perform spoofing over a network.
Discussion
Discussion for this issue can be found at dotnet/msbuild#11846
Mitigation factors
Projects which do not utilize the DownloadFile build task are not susceptible to this vulnerability.
Affected software
Affected Packages
The vulnerability affects any Microsoft .NET Core project if it uses any of affected packages versions listed below
>=16.0.461, <= 16.11.0
>= 17.0.0, <= 17.8.3
>= 17.9.5, <= 17.10.4
17.11.4
17.12.6
17.13.9
16.11.6
17.8.29
17.10.29
17.12.36
17.13.26
17.14.8
Advisory FAQ
How do I know if I am affected?
If you have a .NET SDK with a version listed, or an affected package listed in affected software or affected packages, you're exposed to the vulnerability.
How do I fix the issue?
dotnet --infocommand. You will see output like the following;If you're using .NET 9.0, you should download and install the appropriate SDK:
.NET 9.0.300for Visual Studio 2022 v17.14,.NET 9.0.204for v17.13, or.NET 9.0.106for v17.12. Download from https://dotnet.microsoft.com/download/dotnet-core/9.0.If you're using .NET 8.0, you should download and install the appropriate SDK:
.NET 8.0.409for Visual Studio 2022 v17.11,.NET 8.0.312for v17.10, or.NET 8.0.116for v17.8. Download from https://dotnet.microsoft.com/download/dotnet-core/8.0.Once you have installed the updated SDK, restart your apps for the update to take effect.
Other Information
Reporting Security Issues
If you have found a potential security issue in .NET 8.0 or .NET 9.0, please email details to [email protected]. Reports may qualify for the Microsoft .NET Core & .NET 5 Bounty. Details of the Microsoft .NET Bounty Program including terms and conditions are at https://aka.ms/corebounty.
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/aspnetcore. 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.
References