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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

9.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS

• CVE-2026-70188: 0.94% estimated exploitation activity in the next 30 days; percentile 60.94 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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 retrieved from the dynamic HPACK table instead of treating them as malformed. Announcement Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/462 CVSS Details - Version: 3.1 - Severity: Critical - Score: 9.1 - Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N - Weakness: CWE-444 (Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')) Affected Platforms - Platforms: Windows, Linux, macOS - Architectures: All <a name="affected-packages"</aAffected Packages The vulnerability affects Microsoft .NET projects that use an affected package version listed below. Package name |…

Published by the source

13 Oct 2026, 20:37 UTC

Last modified by the source

19 Oct 2026, 19:30 UTC

Source last checked

26 Oct 2026, 17:05 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-fpq8-4vhr-rcxx

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-fpq8-4vhr-rcxx

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# Patch Next advisory brief: CVE-2026-70188

Advisory: Microsoft Security Advisory CVE-2026-70188 - ASP.NET Core Security Feature Bypass Vulnerability
IDs: CVE-2026-70188, GHSA-fpq8-4vhr-rcxx
Record: https://patchnext.com/advisories/cve-2026-70188 (revision 2, source checked 26 Oct 2026, 17:05 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: microsoft.aspnetcore.app.runtime.linux-arm64 11.0.0-rc.2, 10.0.13, 9.0.21, 8.0.32; microsoft.aspnetcore.app.runtime.linux-musl-arm64 11.0.0-rc.2, 10.0.13, 9.0.21, 8.0.32; microsoft.aspnetcore.app.runtime.osx-x64 11.0.0-rc.2, 10.0.13, 9.0.21, 8.0.32; microsoft.aspnetcore.app.runtime.linux-arm 11.0.0-rc.2, 10.0.13, 9.0.21, 8.0.32; microsoft.aspnetcore.app.runtime.win-x86 11.0.0-rc.2, 10.0.13, 9.0.21, 8.0.32; microsoft.aspnetcore.app.runtime.linux-x64 11.0.0-rc.2, 10.0.13, 9.0.21, 8.0.32; microsoft.aspnetcore.app.runtime.linux-musl-arm 11.0.0-rc.2, 10.0.13, 9.0.21, 8.0.32; microsoft.aspnetcore.app.runtime.linux-musl-x64 11.0.0-rc.2, 10.0.13, 9.0.21, 8.0.32; microsoft.aspnetcore.app.runtime.osx-arm64 11.0.0-rc.2, 10.0.13, 9.0.21, 8.0.32; microsoft.aspnetcore.app.runtime.win-x64 11.0.0-rc.2, 10.0.13, 9.0.21, 8.0.32; microsoft.aspnetcore.app.runtime.win-arm64 11.0.0-rc.2, 10.0.13, 9.0.21, 8.0.32. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet microsoft.aspnetcore.app.runtime.linux-arm64: affected >= 11.0.0-preview.1, <= 11.0.0-rc.1; >= 8.0.0, <= 8.0.31; >= 10.0.0, <= 10.0.12; >= 9.0.0, <= 9.0.20; fixed in 11.0.0-rc.2, 10.0.13, 8.0.32, 9.0.21
- NuGet microsoft.aspnetcore.app.runtime.linux-musl-arm64: affected >= 11.0.0-preview.1, <= 11.0.0-rc.1; >= 8.0.0, <= 8.0.31; >= 10.0.0, <= 10.0.12; >= 9.0.0, <= 9.0.20; fixed in 11.0.0-rc.2, 10.0.13, 8.0.32, 9.0.21
- NuGet microsoft.aspnetcore.app.runtime.osx-x64: affected >= 11.0.0-preview.1, <= 11.0.0-rc.1; >= 8.0.0, <= 8.0.31; >= 10.0.0, <= 10.0.12; >= 9.0.0, <= 9.0.20; fixed in 11.0.0-rc.2, 10.0.13, 8.0.32, 9.0.21
- NuGet microsoft.aspnetcore.app.runtime.linux-arm: affected >= 11.0.0-preview.1, <= 11.0.0-rc.1; >= 8.0.0, <= 8.0.31; >= 10.0.0, <= 10.0.12; >= 9.0.0, <= 9.0.20; fixed in 11.0.0-rc.2, 10.0.13, 8.0.32, 9.0.21
- NuGet microsoft.aspnetcore.app.runtime.win-x86: affected >= 11.0.0-preview.1, <= 11.0.0-rc.1; >= 8.0.0, <= 8.0.31; >= 10.0.0, <= 10.0.12; >= 9.0.0, <= 9.0.20; fixed in 11.0.0-rc.2, 10.0.13, 8.0.32, 9.0.21
- NuGet microsoft.aspnetcore.app.runtime.linux-x64: affected >= 11.0.0-preview.1, <= 11.0.0-rc.1; >= 8.0.0, <= 8.0.31; >= 10.0.0, <= 10.0.12; >= 9.0.0, <= 9.0.20; fixed in 11.0.0-rc.2, 10.0.13, 8.0.32, 9.0.21
- NuGet microsoft.aspnetcore.app.runtime.linux-musl-arm: affected >= 11.0.0-preview.1, <= 11.0.0-rc.1; >= 8.0.0, <= 8.0.31; >= 10.0.0, <= 10.0.12; >= 9.0.0, <= 9.0.20; fixed in 11.0.0-rc.2, 10.0.13, 8.0.32, 9.0.21
- NuGet microsoft.aspnetcore.app.runtime.linux-musl-x64: affected >= 11.0.0-preview.1, <= 11.0.0-rc.1; >= 8.0.0, <= 8.0.31; >= 10.0.0, <= 10.0.12; >= 9.0.0, <= 9.0.20; fixed in 11.0.0-rc.2, 10.0.13, 8.0.32, 9.0.21
- NuGet microsoft.aspnetcore.app.runtime.osx-arm64: affected >= 11.0.0-preview.1, <= 11.0.0-rc.1; >= 8.0.0, <= 8.0.31; >= 10.0.0, <= 10.0.12; >= 9.0.0, <= 9.0.20; fixed in 11.0.0-rc.2, 10.0.13, 8.0.32, 9.0.21
- NuGet microsoft.aspnetcore.app.runtime.win-x64: affected >= 11.0.0-preview.1, <= 11.0.0-rc.1; >= 8.0.0, <= 8.0.31; >= 10.0.0, <= 10.0.12; >= 9.0.0, <= 9.0.20; fixed in 11.0.0-rc.2, 10.0.13, 8.0.32, 9.0.21
- NuGet microsoft.aspnetcore.app.runtime.win-arm64: affected >= 11.0.0-preview.1, <= 11.0.0-rc.1; >= 8.0.0, <= 8.0.31; >= 10.0.0, <= 10.0.12; >= 9.0.0, <= 9.0.20; fixed in 11.0.0-rc.2, 10.0.13, 8.0.32, 9.0.21

## Suggested inspection (read-only)
- NuGet microsoft.aspnetcore.app.runtime.linux-arm64: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.linux-musl-arm64: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.osx-x64: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.linux-arm: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.win-x86: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.linux-x64: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.linux-musl-arm: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.linux-musl-x64: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.osx-arm64: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.win-x64: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.win-arm64: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on microsoft.aspnetcore.app.runtime.linux-arm64, microsoft.aspnetcore.app.runtime.linux-musl-arm64, microsoft.aspnetcore.app.runtime.osx-x64, microsoft.aspnetcore.app.runtime.linux-arm, microsoft.aspnetcore.app.runtime.win-x86, microsoft.aspnetcore.app.runtime.linux-x64, microsoft.aspnetcore.app.runtime.linux-musl-arm, microsoft.aspnetcore.app.runtime.linux-musl-x64, microsoft.aspnetcore.app.runtime.osx-arm64, microsoft.aspnetcore.app.runtime.win-x64, microsoft.aspnetcore.app.runtime.win-arm64.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-fpq8-4vhr-rcxx (OSV record GHSA-fpq8-4vhr-rcxx lists affected ranges: NuGet microsoft.aspnetcore.app.runtime.linux-arm >=11.0.0-preview.1 =8.0.0 =10.0.0 =9.0.0 =11.0.0-preview.1 =8.0.0 =10.0.0 =9.0.0 =11.0.0-preview.1 =8.0.0…)
- Verified: https://github.com/advisories/GHSA-fpq8-4vhr-rcxx (GitHub-reviewed advisory GHSA-fpq8-4vhr-rcxx lists affected ranges: NuGet microsoft.aspnetcore.app.runtime.linux-arm >=11.0.0-preview.1 =8.0.0 =10.0.0 =9.0.0 =11.0.0-preview.1 =8.0.0 =10.0.0 =9.0.0 =11.0.0-preview.1 =8.0.0 =10.0.0 =9.0.0 <=9.0.20; NuGet…)

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