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High, CVSS 7.5

ASP.NET Core and Visual Studio Denial of Service Vulnerability

CVE-2021-1723GHSA-242j-2gm6-5rwx

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (microsoft.aspnetcore.app.runtime.linux-arm64 5.0.2, 3.1.11; microsoft.aspnetcore.app.runtime.linux-musl-arm64 5.0.2, 3.1.11; microsoft.aspnetcore.app.runtime.osx-x64 5.0.2, 3.1.11; microsoft.aspnetcore.app.runtime.linux-arm 5.0.2, 3.1.11; microsoft.aspnetcore.app.runtime.win-x86 5.0.2, 3.1.11; 7 more packages under Affected packages), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

  • GitHub Advisory Database and maintainer security advisories on GitHub

    GitHub-reviewed advisory GHSA-242j-2gm6-5rwx lists affected ranges: NuGet microsoft.aspnetcore.server.kestrel.core >=0 =3.1.0 =5.0.0 =3.1.0 =5.0.0 =3.1.0 =5.0.0 =3.1.0 =5.0.0 <5.0.2; NuGet…

    VerifiedObserved Structured GitHub Advisory Database record (type=reviewed) from the GitHub REST API.

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS
  • CVE-2021-1723: 5.30% estimated exploitation activity in the next 30 days; percentile 92.59 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

A denial-of-service vulnerability exists in the way Kestrel parses HTTP/2 requests. The security update addresses the vulnerability by fixing the way the Kestrel parses HTTP/2 requests. Users are advised to upgrade.

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 1 · created ·

    Published from ghsa record GHSA-242j-2gm6-5rwx

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2021-1723

Advisory: ASP.NET Core and Visual Studio Denial of Service Vulnerability
IDs: CVE-2021-1723, GHSA-242j-2gm6-5rwx
Record: https://patchnext.com/advisories/cve-2021-1723 (revision 1, source checked 26 Oct 2026, 17:00 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
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 5.0.2, 3.1.11; microsoft.aspnetcore.app.runtime.linux-musl-arm64 5.0.2, 3.1.11; microsoft.aspnetcore.app.runtime.osx-x64 5.0.2, 3.1.11; microsoft.aspnetcore.app.runtime.linux-arm 5.0.2, 3.1.11; microsoft.aspnetcore.app.runtime.win-x86 5.0.2, 3.1.11; microsoft.aspnetcore.app.runtime.linux-x64 5.0.2, 3.1.11; microsoft.aspnetcore.app.runtime.linux-musl-arm 5.0.2; microsoft.aspnetcore.app.runtime.win-arm 5.0.2, 3.1.11; microsoft.aspnetcore.app.runtime.linux-musl-x64 5.0.2, 3.1.11; microsoft.aspnetcore.server.kestrel.core 2.1.25; microsoft.aspnetcore.app.runtime.win-x64 5.0.2, 3.1.11; microsoft.aspnetcore.app.runtime.win-arm64 5.0.2, 3.1.11. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet microsoft.aspnetcore.app.runtime.linux-arm64: affected >= 3.1.0, < 3.1.11; >= 5.0.0, < 5.0.2; fixed in 3.1.11, 5.0.2
- NuGet microsoft.aspnetcore.app.runtime.linux-musl-arm64: affected >= 3.1.0, < 3.1.11; >= 5.0.0, < 5.0.2; fixed in 3.1.11, 5.0.2
- NuGet microsoft.aspnetcore.app.runtime.osx-x64: affected >= 3.1.0, < 3.1.11; >= 5.0.0, < 5.0.2; fixed in 3.1.11, 5.0.2
- NuGet microsoft.aspnetcore.app.runtime.linux-arm: affected >= 3.1.0, < 3.1.11; >= 5.0.0, < 5.0.2; fixed in 3.1.11, 5.0.2
- NuGet microsoft.aspnetcore.app.runtime.win-x86: affected >= 3.1.0, < 3.1.11; >= 5.0.0, < 5.0.2; fixed in 3.1.11, 5.0.2
- NuGet microsoft.aspnetcore.app.runtime.linux-x64: affected >= 3.1.0, < 3.1.11; >= 5.0.0, < 5.0.2; fixed in 3.1.11, 5.0.2
- NuGet microsoft.aspnetcore.app.runtime.linux-musl-arm: affected >= 5.0.1, <= 5.0.1; fixed in 5.0.2
- NuGet microsoft.aspnetcore.app.runtime.win-arm: affected >= 3.1.0, < 3.1.11; >= 5.0.0, < 5.0.2; fixed in 3.1.11, 5.0.2
- NuGet microsoft.aspnetcore.app.runtime.linux-musl-x64: affected >= 3.1.0, < 3.1.11; >= 5.0.0, < 5.0.2; fixed in 3.1.11, 5.0.2
- NuGet microsoft.aspnetcore.server.kestrel.core: affected < 2.1.25; fixed in 2.1.25
- NuGet microsoft.aspnetcore.app.runtime.win-x64: affected >= 3.1.0, < 3.1.11; >= 5.0.0, < 5.0.2; fixed in 3.1.11, 5.0.2
- NuGet microsoft.aspnetcore.app.runtime.win-arm64: affected >= 3.1.0, < 3.1.11; >= 5.0.0, < 5.0.2; fixed in 3.1.11, 5.0.2

## 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.win-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.server.kestrel.core: 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.win-arm, microsoft.aspnetcore.app.runtime.linux-musl-x64, microsoft.aspnetcore.server.kestrel.core, 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://github.com/advisories/GHSA-242j-2gm6-5rwx (GitHub-reviewed advisory GHSA-242j-2gm6-5rwx lists affected ranges: NuGet microsoft.aspnetcore.server.kestrel.core >=0 =3.1.0 =5.0.0 =3.1.0 =5.0.0 =3.1.0 =5.0.0 =3.1.0 =5.0.0 <5.0.2; NuGet…)

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