CVE-2026-56170: Microsoft Security Advisory CVE-2026-56170 – .NET Denial of Service Vulnerability

Microsoft is releasing this security advisory to provide information about a vulnerability in ASP.NET Core SignalR (Microsoft.AspNetCore.App.Runtime). This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.

A denial of service vulnerability exists in ASP.NET Core SignalR in .NET 8, .NET 9, and .NET 10. Stateful reconnect can be leveraged by an attacker to deny service to other users.