GHSA-8prm-248r-h957: Microsoft Security Advisory CVE-2026-47300 – .NET Elevation of Privilege Vulnerability

Executive summary Microsoft is releasing this security advisory to provide information about a vulnerability in ASP.NET Core Negotiate Authentication (Microsoft.AspNetCore.Authentication.Negotiate). This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability. An elevation of privilege vulnerability exists in the ASP.NET Core Negotiate authentication handler in .NET 8, .NET 9, and .NET 10 due to improper validation. Announcement Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/TBD CVSS Details - Version: 3.1 - Severity: High - Score: 8.8 - Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H - Weakness: CWE-303 (Incorrect Implementation of Authentication Algorithm) Affected Platforms - Platforms: All - Architectures: All Mitigation Factors Your ASP.NET Core app is only affected if it uses Negotiate authentication and LDAP to retrieve role information. <a name="affected-packages"></a>Affected Packages The vulnerability affects any Microsoft .NET project if it uses any of affected package versions listed below <a name=".NET 10.0"></a>.NET 10.0 Package name | Affected version | Patched version ------------ | ---------------- | ------------------------- Microsoft.AspNetCore.Authentication.Negotiate | >= 10.0.0, <= 10.0.9 | 10.0.10 <a name=".NET 9.0"></a>.NET 9.0 Package name | Affected version | Patched version ------------ | ---------------- | ------------------------- Microsoft.AspNetCore.Authentication.Negotiate | >= 9.0.0, <= 9.0.17 | 9.0.18 <a name=".NET 8.0"></a>.NET 8.0 Package name | Affected version | Patched version ------------ | ---------------- | ------------------------- Microsoft.AspNetCore.Authentication.Negotiate | >= 8.0.0, <= 8.0.28 | 8.0.29 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