CVE-2026-70194

Improper certificate validation in .NET Framework allows an unauthorized attacker to bypass a security feature over a network.

Improper certificate validation in .NET Framework allows an unauthorized attacker to bypass a security feature over a network.

Executive summary

Microsoft is releasing this security advisory to provide information about a vulnerability in System.Net.Security. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.

.NET 11 post-handshake TLS client authentication can fail to verify the client certificate, allowing mutual-authentication requirements to be bypassed.

Announcement

Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/464

CVSS Details

• Version: 3.1

• Severity: Moderate

• Score: 6.5

• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

• Weakness: CWE-295 (Improper Certificate Validation)

Affected Platforms

• Platforms: Linux, macOS
• Architectures: All

<a name="affected-packages"></a>Affected Packages

The vulnerability affects Microsoft .NET projects that use an affected package version listed below.

Package name | Affected version | Patched version ------------ | ---------------- | --------------- Microsoft.NETCore.App.Runtime.linux-arm | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.linux-arm64 | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.linux-musl-arm | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.linux-musl-arm64 | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.linux-musl-x64 | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.linux-x64 | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.osx-arm64 | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.osx-x64 | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2

Advisory FAQ

<a name="how-affected"></a>How do I know if I am affected?

If using a package listed in 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. 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.

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 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 a supported version of .NET, please report it to the Microsoft Security Response Center (MSRC) via the MSRC Researcher Portal. Further information can be found in the MSRC Report an Issue FAQ.

Security reports made through MSRC may qualify for the Microsoft .NET Bounty. Details of the Microsoft .NET Bounty Program including terms and…

Improper certificate validation in .NET Framework allows an unauthorized attacker to bypass a security feature over a network.

Executive summary

Microsoft is releasing this security advisory to provide information about a vulnerability in System.Net.Security. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.

.NET 11 post-handshake TLS client authentication can fail to verify the client certificate, allowing mutual-authentication requirements to be bypassed.

Announcement

Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/464

CVSS Details

• Version: 3.1

• Severity: Moderate

• Score: 6.5

• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

• Weakness: CWE-295 (Improper Certificate Validation)

Affected Platforms

• Platforms: Linux, macOS
• Architectures: All

<a name="affected-packages"></a>Affected Packages

The vulnerability affects Microsoft .NET projects that use an affected package version listed below.

Package name | Affected version | Patched version ------------ | ---------------- | --------------- Microsoft.NETCore.App.Runtime.linux-arm | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.linux-arm64 | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.linux-musl-arm | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.linux-musl-arm64 | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.linux-musl-x64 | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.linux-x64 | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.osx-arm64 | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.osx-x64 | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2

Advisory FAQ

<a name="how-affected"></a>How do I know if I am affected?

If using a package listed in 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. 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.

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 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 a supported version of .NET, please report it to the Microsoft Security Response Center (MSRC) via the MSRC Researcher Portal. Further information can be found in the MSRC Report an Issue FAQ.

Security reports made through MSRC may qualify for the Microsoft .NET Bounty. Details of the Microsoft .NET Bounty Program including terms and…

Improper certificate validation in .NET Framework allows an unauthorized attacker to bypass a security feature over a network.

Multiple security issues were discovered in .NET and this update includes new upstream .NET versions to fix these issues.

.NET 8 has been updated to 8.0.32 in Ubuntu 22.04 LTS and Ubuntu 24.04 LTS. .NET 10 has been updated to 10.0.13 in Ubuntu 24.04 LTS, Ubuntu 26.04 LTS and Ubuntu 26.10. .NET 11 has been updated to 11.0.0~rc2 in Ubuntu 26.10.

In addition to security fixes, the updated packages contain bug fixes, new features, and possibly incompatible changes.