CVE-2026-70188: Microsoft Security Advisory CVE-2026-70188 - ASP.NET Core Security Feature Bypass 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.

Kestrel accepts newline characters in HTTP/2 request trailers and values retrieved from the dynamic HPACK table instead of treating them as malformed.

References

github.com/advisories/GHSA-fpq8-4vhr-rcxx
github.com/dotnet/announcements/issues/462
github.com/dotnet/aspnetcore/discussions/69798
github.com/dotnet/aspnetcore/security/advisories/GHSA-fpq8-4vhr-rcxx
msrc.microsoft.com/update-guide/vulnerability/CVE-2026-70188
nvd.nist.gov/vuln/detail/CVE-2026-70188

Code Behaviors & Features

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