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

Microsoft.AspNetCore.App.Runtime.linux-arm (nuget), Microsoft.AspNetCore.App.Runtime.linux-arm64 (nuget), Microsoft.AspNetCore.App.Runtime.linux-musl-arm (nuget), Microsoft.AspNetCore.App.Runtime.linux-musl-arm64 (nuget) +7 more

## Executive summary 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…

First seen: 13 Oct 2026
Last update: 13 Oct 2026, 20:37 UTC
Fixed in: Microsoft.AspNetCore.App.Runtime.linux-arm 11.0.0-rc.2
Microsoft.AspNetCore.App.Runtime.linux-arm64 11.0.0-rc.2
Microsoft.AspNetCore.App.Runtime.linux-musl-arm 11.0.0-rc.2
Microsoft.AspNetCore.App.Runtime.linux-musl-arm64 11.0.0-rc.2
Microsoft.AspNetCore.App.Runtime.linux-musl-x64 11.0.0-rc.2
Microsoft.AspNetCore.App.Runtime.linux-x64 11.0.0-rc.2
Microsoft.AspNetCore.App.Runtime.osx-arm64 11.0.0-rc.2
Microsoft.AspNetCore.App.Runtime.osx-x64 11.0.0-rc.2
Microsoft.AspNetCore.App.Runtime.win-arm64 11.0.0-rc.2
Microsoft.AspNetCore.App.Runtime.win-x64 11.0.0-rc.2
Microsoft.AspNetCore.App.Runtime.win-x86 11.0.0-rc.2
Microsoft.AspNetCore.App.Runtime.linux-arm 8.0.32
Microsoft.AspNetCore.App.Runtime.linux-arm64 8.0.32
Microsoft.AspNetCore.App.Runtime.linux-musl-arm 8.0.32
Microsoft.AspNetCore.App.Runtime.linux-musl-arm64 8.0.32
Microsoft.AspNetCore.App.Runtime.linux-musl-x64 8.0.32
Microsoft.AspNetCore.App.Runtime.linux-x64 8.0.32
Microsoft.AspNetCore.App.Runtime.osx-arm64 8.0.32
Microsoft.AspNetCore.App.Runtime.osx-x64 8.0.32
Microsoft.AspNetCore.App.Runtime.win-arm64 8.0.32
Microsoft.AspNetCore.App.Runtime.win-x64 8.0.32
Microsoft.AspNetCore.App.Runtime.win-x86 8.0.32
Microsoft.AspNetCore.App.Runtime.linux-arm 10.0.13
Microsoft.AspNetCore.App.Runtime.linux-arm64 10.0.13
Microsoft.AspNetCore.App.Runtime.linux-musl-arm 10.0.13
Microsoft.AspNetCore.App.Runtime.linux-musl-arm64 10.0.13
Microsoft.AspNetCore.App.Runtime.linux-musl-x64 10.0.13
Microsoft.AspNetCore.App.Runtime.linux-x64 10.0.13
Microsoft.AspNetCore.App.Runtime.osx-arm64 10.0.13
Microsoft.AspNetCore.App.Runtime.osx-x64 10.0.13
Microsoft.AspNetCore.App.Runtime.win-arm64 10.0.13
Microsoft.AspNetCore.App.Runtime.win-x64 10.0.13
Microsoft.AspNetCore.App.Runtime.win-x86 10.0.13
Microsoft.AspNetCore.App.Runtime.linux-arm 9.0.21
Microsoft.AspNetCore.App.Runtime.linux-arm64 9.0.21
Microsoft.AspNetCore.App.Runtime.linux-musl-arm 9.0.21
Microsoft.AspNetCore.App.Runtime.linux-musl-arm64 9.0.21
Microsoft.AspNetCore.App.Runtime.linux-musl-x64 9.0.21
Microsoft.AspNetCore.App.Runtime.linux-x64 9.0.21
Microsoft.AspNetCore.App.Runtime.osx-arm64 9.0.21
Microsoft.AspNetCore.App.Runtime.osx-x64 9.0.21
Microsoft.AspNetCore.App.Runtime.win-arm64 9.0.21
Microsoft.AspNetCore.App.Runtime.win-x64 9.0.21
Microsoft.AspNetCore.App.Runtime.win-x86 9.0.21
Identifiers: CVE-2026-70188
CVSS: 9.1
Source: GitHub advisory
On the menu as: Linux kernel

Check this repository for exposure to one security incident from pwned.coffee. Report first, change nothing until I say so.

## Microsoft Security Advisory CVE-2026-70188 - ASP.NET Core Security Feature Bypass Vulnerability
Severity: critical. Patch status: patched.
Affected: Microsoft.AspNetCore.App.Runtime.linux-arm (nuget), Microsoft.AspNetCore.App.Runtime.linux-arm64 (nuget), Microsoft.AspNetCore.App.Runtime.linux-musl-arm (nuget), Microsoft.AspNetCore.App.Runtime.linux-musl-arm64 (nuget) +7 more
Fixed in: Microsoft.AspNetCore.App.Runtime.linux-arm 11.0.0-rc.2, Microsoft.AspNetCore.App.Runtime.linux-arm64 11.0.0-rc.2, Microsoft.AspNetCore.App.Runtime.linux-musl-arm 11.0.0-rc.2, Microsoft.AspNetCore.App.Runtime.linux-musl-arm64 11.0.0-rc.2, Microsoft.AspNetCore.App.Runtime.linux-musl-x64 11.0.0-rc.2, Microsoft.AspNetCore.App.Runtime.linux-x64 11.0.0-rc.2, Microsoft.AspNetCore.App.Runtime.osx-arm64 11.0.0-rc.2, Microsoft.AspNetCore.App.Runtime.osx-x64 11.0.0-rc.2, Microsoft.AspNetCore.App.Runtime.win-arm64 11.0.0-rc.2, Microsoft.AspNetCore.App.Runtime.win-x64 11.0.0-rc.2, Microsoft.AspNetCore.App.Runtime.win-x86 11.0.0-rc.2, Microsoft.AspNetCore.App.Runtime.linux-arm 8.0.32, Microsoft.AspNetCore.App.Runtime.linux-arm64 8.0.32, Microsoft.AspNetCore.App.Runtime.linux-musl-arm 8.0.32, Microsoft.AspNetCore.App.Runtime.linux-musl-arm64 8.0.32, Microsoft.AspNetCore.App.Runtime.linux-musl-x64 8.0.32, Microsoft.AspNetCore.App.Runtime.linux-x64 8.0.32, Microsoft.AspNetCore.App.Runtime.osx-arm64 8.0.32, Microsoft.AspNetCore.App.Runtime.osx-x64 8.0.32, Microsoft.AspNetCore.App.Runtime.win-arm64 8.0.32, Microsoft.AspNetCore.App.Runtime.win-x64 8.0.32, Microsoft.AspNetCore.App.Runtime.win-x86 8.0.32, Microsoft.AspNetCore.App.Runtime.linux-arm 10.0.13, Microsoft.AspNetCore.App.Runtime.linux-arm64 10.0.13, Microsoft.AspNetCore.App.Runtime.linux-musl-arm 10.0.13, Microsoft.AspNetCore.App.Runtime.linux-musl-arm64 10.0.13, Microsoft.AspNetCore.App.Runtime.linux-musl-x64 10.0.13, Microsoft.AspNetCore.App.Runtime.linux-x64 10.0.13, Microsoft.AspNetCore.App.Runtime.osx-arm64 10.0.13, Microsoft.AspNetCore.App.Runtime.osx-x64 10.0.13, Microsoft.AspNetCore.App.Runtime.win-arm64 10.0.13, Microsoft.AspNetCore.App.Runtime.win-x64 10.0.13, Microsoft.AspNetCore.App.Runtime.win-x86 10.0.13, Microsoft.AspNetCore.App.Runtime.linux-arm 9.0.21, Microsoft.AspNetCore.App.Runtime.linux-arm64 9.0.21, Microsoft.AspNetCore.App.Runtime.linux-musl-arm 9.0.21, Microsoft.AspNetCore.App.Runtime.linux-musl-arm64 9.0.21, Microsoft.AspNetCore.App.Runtime.linux-musl-x64 9.0.21, Microsoft.AspNetCore.App.Runtime.linux-x64 9.0.21, Microsoft.AspNetCore.App.Runtime.osx-arm64 9.0.21, Microsoft.AspNetCore.App.Runtime.osx-x64 9.0.21, Microsoft.AspNetCore.App.Runtime.win-arm64 9.0.21, Microsoft.AspNetCore.App.Runtime.win-x64 9.0.21, Microsoft.AspNetCore.App.Runtime.win-x86 9.0.21
Ids: CVE-2026-70188

## Executive summary 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…

## Steps
1. Search every lockfile and manifest (package-lock.json, yarn.lock, pnpm-lock.yaml, requirements*.txt, poetry.lock, uv.lock, composer.lock, go.sum, Cargo.lock, Gemfile.lock) for `Microsoft.AspNetCore.App.Runtime.linux-arm`, `Microsoft.AspNetCore.App.Runtime.linux-arm64`, `Microsoft.AspNetCore.App.Runtime.linux-musl-arm`, `Microsoft.AspNetCore.App.Runtime.linux-musl-arm64`, `Microsoft.AspNetCore.App.Runtime.linux-musl-x64`, `Microsoft.AspNetCore.App.Runtime.linux-x64`, `Microsoft.AspNetCore.App.Runtime.osx-arm64`, `Microsoft.AspNetCore.App.Runtime.osx-x64`, `Microsoft.AspNetCore.App.Runtime.win-arm64`, `Microsoft.AspNetCore.App.Runtime.win-x64`, `Microsoft.AspNetCore.App.Runtime.win-x86`. For each hit, compare the installed version with the fix on the same major line: Microsoft.AspNetCore.App.Runtime.linux-arm 11.0.0-rc.2, Microsoft.AspNetCore.App.Runtime.linux-arm64 11.0.0-rc.2, Microsoft.AspNetCore.App.Runtime.linux-musl-arm 11.0.0-rc.2, Microsoft.AspNetCore.App.Runtime.linux-musl-arm64 11.0.0-rc.2, Microsoft.AspNetCore.App.Runtime.linux-musl-x64 11.0.0-rc.2, Microsoft.AspNetCore.App.Runtime.linux-x64 11.0.0-rc.2, Microsoft.AspNetCore.App.Runtime.osx-arm64 11.0.0-rc.2, Microsoft.AspNetCore.App.Runtime.osx-x64 11.0.0-rc.2, Microsoft.AspNetCore.App.Runtime.win-arm64 11.0.0-rc.2, Microsoft.AspNetCore.App.Runtime.win-x64 11.0.0-rc.2, Microsoft.AspNetCore.App.Runtime.win-x86 11.0.0-rc.2, Microsoft.AspNetCore.App.Runtime.linux-arm 8.0.32, Microsoft.AspNetCore.App.Runtime.linux-arm64 8.0.32, Microsoft.AspNetCore.App.Runtime.linux-musl-arm 8.0.32, Microsoft.AspNetCore.App.Runtime.linux-musl-arm64 8.0.32, Microsoft.AspNetCore.App.Runtime.linux-musl-x64 8.0.32, Microsoft.AspNetCore.App.Runtime.linux-x64 8.0.32, Microsoft.AspNetCore.App.Runtime.osx-arm64 8.0.32, Microsoft.AspNetCore.App.Runtime.osx-x64 8.0.32, Microsoft.AspNetCore.App.Runtime.win-arm64 8.0.32, Microsoft.AspNetCore.App.Runtime.win-x64 8.0.32, Microsoft.AspNetCore.App.Runtime.win-x86 8.0.32, Microsoft.AspNetCore.App.Runtime.linux-arm 10.0.13, Microsoft.AspNetCore.App.Runtime.linux-arm64 10.0.13, Microsoft.AspNetCore.App.Runtime.linux-musl-arm 10.0.13, Microsoft.AspNetCore.App.Runtime.linux-musl-arm64 10.0.13, Microsoft.AspNetCore.App.Runtime.linux-musl-x64 10.0.13, Microsoft.AspNetCore.App.Runtime.linux-x64 10.0.13, Microsoft.AspNetCore.App.Runtime.osx-arm64 10.0.13, Microsoft.AspNetCore.App.Runtime.osx-x64 10.0.13, Microsoft.AspNetCore.App.Runtime.win-arm64 10.0.13, Microsoft.AspNetCore.App.Runtime.win-x64 10.0.13, Microsoft.AspNetCore.App.Runtime.win-x86 10.0.13, Microsoft.AspNetCore.App.Runtime.linux-arm 9.0.21, Microsoft.AspNetCore.App.Runtime.linux-arm64 9.0.21, Microsoft.AspNetCore.App.Runtime.linux-musl-arm 9.0.21, Microsoft.AspNetCore.App.Runtime.linux-musl-arm64 9.0.21, Microsoft.AspNetCore.App.Runtime.linux-musl-x64 9.0.21, Microsoft.AspNetCore.App.Runtime.linux-x64 9.0.21, Microsoft.AspNetCore.App.Runtime.osx-arm64 9.0.21, Microsoft.AspNetCore.App.Runtime.osx-x64 9.0.21, Microsoft.AspNetCore.App.Runtime.win-arm64 9.0.21, Microsoft.AspNetCore.App.Runtime.win-x64 9.0.21, Microsoft.AspNetCore.App.Runtime.win-x86 9.0.21. If it's lower, give the exact upgrade command for the package manager this repo uses.
2. This touches infrastructure (linux). Look in terraform, ansible, cloud-init, Dockerfiles and docs for the product and version we run. If it isn't in the repo, say so and list what a human should check on the box.

## Report
A table: file, product or package, version in use, affected yes/no, exact fix. Then anything a human has to check outside the repo.

If you have the pwned.coffee MCP server (https://pwned.coffee/mcp), call lookup_cve("CVE-2026-70188") for the latest, and check_repo with this repo's lockfiles, Dockerfiles and workflows for a full receipt.
Sources: https://github.com/advisories/GHSA-fpq8-4vhr-rcxx https://github.com/dotnet/announcements/issues/462 https://github.com/dotnet/aspnetcore/discussions/69798 https://github.com/dotnet/aspnetcore/security/advisories/GHSA-fpq8-4vhr-rcxx https://nvd.nist.gov/vuln/detail/CVE-2026-70188
https://pwned.coffee/i/microsoft-security-advisory-cve-2026-70188-asp-net-core-security-feature

Sources

Totalone very hot coffee