Microsoft Security Advisory CVE-2026-118746 - .NET Security Feature Bypass Vulnerability

Executive summary

Microsoft is releasing this security advisory to provide information about a vulnerability in .NET. This advisory provides guidance on updating affected applications and components.

Unix Negotiate authentication can accept a request when required channel-binding information is missing.

Announcement

Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/498

CVSS Details

• Version: 3.1
• Severity: Medium
• Score: 6.8 (base score)
• Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N/E:U/RL:O/RC:C
• Weakness: CWE-636

Affected Platforms

• Platforms: Linux, macOS
• Architectures: Arm, Arm64, x64

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

The tables list affected .NET 11 runtime package versions and fixed versions. The issue occurs during server-side Negotiate authentication with PolicyEnforcement.Always when the client omits the channel-binding token.

.NET 11.0 - Linux runtime packages

The six Linux runtime packages at version 11.0.0-preview.7.26381.103 reject PolicyEnforcement.Always before authentication and are not affected.

.NET 11.0 - macOS runtime packages

The macOS runtime packages at versions 11.0.0-preview.7.26381.103, 11.0.0-rc.1.26425.128, 11.0.0-rc.2.26504.105, and 11.0.0-rc.3.26522.148 reject PolicyEnforcement.Always before authentication and are not affected.

Advisory FAQ

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

Applications using server-side Negotiate authentication with PolicyEnforcement.Always are affected when their runtime package version is in the platform-specific ranges above. On Linux, this includes .NET 11 previews 1 through 6 and release candidates 1 through 3. On macOS, this includes .NET 11 previews 1 through 6. Preview 7 is not affected on either platform, and macOS release candidates 1 through 3 are not affected. Self-contained applications include their own runtime; updating a machine-wide runtime does not replace it.

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

For affected Linux and macOS .NET 11 prereleases, install .NET 11.0.0 or update each independently referenced runtime package to 11.0.0. Restart applications. Rebuild and redeploy self-contained applications; updating a machine-wide runtime does not replace their embedded runtime. An SDK update alone does not update an application's standalone package references.

On macOS, PolicyEnforcement.Always remains unsupported and throws PlatformNotSupportedException. The update prevents authentication from proceeding without the required protection; it does not add Extended Protection support on macOS.

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 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/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-2026-118746

Acknowledgements

• Alejandro Pacheco
• Anonymous
• Markus Magnuson

Revisions

V1.0 (November 10, 2026): Advisory published.