CVE-2026-47303: Microsoft Security Advisory CVE-2026-47303 – .NET Elevation of Privilege Vulnerability

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 parsing.