CVE-2026-70186: Microsoft Security Advisory CVE-2026-70186 - ASP.NET Core Denial of Service Vulnerability

October 13, 2026 (updated October 19, 2026)

Microsoft is releasing this security advisory to provide information about a vulnerability in Microsoft.AspNetCore.Server.Kestrel.Core. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.

An unauthenticated remote attacker can send crafted HTTP/3 reset or abort sequences that deadlock Kestrel connection handling. Repeated requests can cause excessive blocked-thread creation and exhaust server resources, resulting in denial of service.

References

Code Behaviors & Features

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