CVE-2025-26646

External control of file name or path in .NET, Visual Studio, and Build Tools for Visual Studio allows an authorized attacker to perform spoofing over a network.

Microsoft Security Advisory CVE-2025-26646: .NET Spoofing Vulnerability

<a name="executive-summary"></a>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.

Announcement

Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/356

<a name="mitigation-factors"></a>Mitigation factors

Projects which do not utilize the DownloadFile build task are not susceptible to this vulnerability.

<a name="affected-software"></a>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 or .NET 8.0.312 SDK, .NET 8.0.408 or .NET 8.0.409 SDK or earlier.

<a name="affected-packages"></a>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<br />>=16.0.461, <= 16.11.0<br />>= 17.0.0, <= 17.8.3<br/>>= 17.9.5, <= 17.10.4<br />17.11.4<br />17.12.6 <br />17.13.9 | 15.9.30<br />16.11.6<br />17.8.29<br/>17.10.29<br />17.12.36<br />17.13.26 <br />17.14.8

Advisory FAQ

<a name="how-affected"></a>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.

<a name="how-fix"></a>How do I fix the issue?

1. 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.
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 the appropriate SDK: .NET 9.0.300 for Visual Studio 2022 v17.14, .NET 9.0.204 for v17.13, or .NET 9.0.106 for 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 8.0.410 for Visual…

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK 9.0.106 and .NET Runtime 9.0.5.Security Fix(es):

• dotnet: .NET and Visual Studio Spoofing Vulnerability (CVE-2025-26646)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK 8.0.116 and .NET Runtime 8.0.16.Security Fix(es):

• dotnet: .NET and Visual Studio Spoofing Vulnerability (CVE-2025-26646)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK 8.0.116 and .NET Runtime 8.0.16.Security Fix(es):

• dotnet: .NET and Visual Studio Spoofing Vulnerability (CVE-2025-26646)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK 8.0.116 and .NET Runtime 8.0.16.Security Fix(es):

• dotnet: .NET and Visual Studio Spoofing Vulnerability (CVE-2025-26646)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK 9.0.106 and .NET Runtime 9.0.5.Security Fix(es):

• dotnet: .NET and Visual Studio Spoofing Vulnerability (CVE-2025-26646)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Root has patched CVE-2025-26646 in the Microsoft.Build.Tasks.Core package for Root:NuGet. Multiple fixed versions available.

External control of file name or path in .NET, Visual Studio, and Build Tools for Visual Studio allows an authorized attacker to perform spoofing over a network.

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK 9.0.106 and .NET Runtime 9.0.5.Security Fix(es):

• dotnet: .NET and Visual Studio Spoofing Vulnerability (CVE-2025-26646)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK 8.0.116 and .NET Runtime 8.0.16.Security Fix(es):

• dotnet: .NET and Visual Studio Spoofing Vulnerability (CVE-2025-26646)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK 8.0.116 and .NET Runtime 8.0.16.Security Fix(es):

• dotnet: .NET and Visual Studio Spoofing Vulnerability (CVE-2025-26646)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK 8.0.116 and .NET Runtime 8.0.16.Security Fix(es):

• dotnet: .NET and Visual Studio Spoofing Vulnerability (CVE-2025-26646)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK 9.0.106 and .NET Runtime 9.0.5.Security Fix(es):

• dotnet: .NET and Visual Studio Spoofing Vulnerability (CVE-2025-26646)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK 9.0.106 and .NET Runtime 9.0.5.Security Fix(es):

• dotnet: .NET and Visual Studio Spoofing Vulnerability (CVE-2025-26646)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

External control of file name or path in .NET, Visual Studio, and Build Tools for Visual Studio allows an authorized attacker to perform spoofing over a network.

External control of file name or path in .NET, Visual Studio, and Build Tools for Visual Studio allows an authorized attacker to perform spoofing over a network.

It was discovered that .NET did not properly handle file names and paths under certain conditions. An attacker could possibly use this issue to perform spoofing over a network.