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Medium, CVSS 6.5

Denial of service in .NET core

CVE-2021-1721GHSA-3gp9-h8hw-pxpw

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (microsoft.netcore.app.runtime.mono.linux-arm 5.0.3; microsoft.netcore.app.runtime.win-x86 5.0.3, 3.1.12; microsoft.netcore.app.runtime.mono.llvm.aot.linux-arm64 5.0.3; microsoft.netcore.app.host.linux-arm64 3.1.12; microsoft.netcore.app.runtime.android-x86 5.0.3; 40 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-3gp9-h8hw-pxpw lists affected ranges: NuGet microsoft.netcore.app >=2.1.0 =3.1.0 =3.1.0 =3.1.0 =3.1.0 =3.1.0 =3.1.0 <3.1.12; 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
6.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
EPSS
  • CVE-2021-1721: 3.34% estimated exploitation activity in the next 30 days; percentile 88.67 (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.

.NET Core and Visual Studio Denial of Service Vulnerability due to a vulnerability which exists when creating HTTPS web request during X509 certificate chain building.

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

    Published from ghsa record GHSA-3gp9-h8hw-pxpw

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-2021-1721

Advisory: Denial of service in .NET core
IDs: CVE-2021-1721, GHSA-3gp9-h8hw-pxpw
Record: https://patchnext.com/advisories/cve-2021-1721 (revision 1, source checked 26 Oct 2026, 16:58 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: microsoft.netcore.app.runtime.mono.linux-arm 5.0.3; microsoft.netcore.app.runtime.win-x86 5.0.3, 3.1.12; microsoft.netcore.app.runtime.mono.llvm.aot.linux-arm64 5.0.3; microsoft.netcore.app.host.linux-arm64 3.1.12; microsoft.netcore.app.runtime.android-x86 5.0.3; microsoft.netcore.app.runtime.win-arm64 5.0.3, 3.1.12; microsoft.netcore.app.host.win-x86 3.1.12; microsoft.netcore.app.host.linux-arm 3.1.12; microsoft.netcore.app.runtime.mono.linux-arm64 5.0.3; microsoft.netcore.app.runtime.ios-x86 5.0.3; microsoft.netcore.app.runtime.linux-musl-x64 5.0.3, 3.1.12; microsoft.netcore.app.host.linux-musl-arm64 3.1.12; microsoft.netcore.app.host.rhel.6-x64 3.1.12; microsoft.netcore.app.host.win-x64 3.1.12; microsoft.netcore.app.runtime.tvos-arm64 5.0.3; microsoft.netcore.app.host.osx-x64 3.1.12; microsoft.netcore.app.runtime.mono.linux-musl-x64 5.0.3; microsoft.netcore.app.host.linux-x64 3.1.12; microsoft.netcore.app.runtime.linux-arm64 5.0.3, 3.1.12; microsoft.netcore.app.runtime.mono.llvm.linux-arm64 5.0.3; microsoft.netcore.app.runtime.mono.linux-x64 5.0.3; microsoft.netcore.app.runtime.linux-arm 5.0.3, 3.1.12; microsoft.netcore.app.runtime.osx-x64 5.0.3, 3.1.12; microsoft.netcore.app.runtime.browser-wasm 5.0.3; microsoft.netcore.app.host.win-arm 3.1.12; microsoft.netcore.app.runtime.android-arm64 5.0.3; microsoft.netcore.app.runtime.mono.llvm.linux-x64 5.0.3; microsoft.netcore.app.runtime.mono.llvm.aot.osx-x64 5.0.3; microsoft.netcore.app.runtime.linux-x64 5.0.3, 3.1.12; microsoft.netcore.app.runtime.android-x64 5.0.3; microsoft.netcore.app.host.win-arm64 3.1.12; microsoft.netcore.app.runtime.tvos-x64 5.0.3; microsoft.netcore.app.runtime.ios-arm 5.0.3; microsoft.netcore.app.runtime.mono.llvm.aot.linux-x64 5.0.3; microsoft.netcore.app.runtime.ios-x64 5.0.3; microsoft.netcore.app.runtime.linux-musl-arm 5.0.3; microsoft.netcore.app.runtime.mono.osx-x64 5.0.3; microsoft.netcore.app 2.1.25; microsoft.netcore.app.host.linux-musl-x64 3.1.12; microsoft.netcore.app.runtime.win-arm 5.0.3, 3.1.12; microsoft.netcore.app.runtime.mono.llvm.osx-x64 5.0.3; microsoft.netcore.app.runtime.rhel.6-x64 3.1.12; microsoft.netcore.app.runtime.linux-musl-arm64 5.0.3, 3.1.12; microsoft.netcore.app.runtime.android-arm 5.0.3; microsoft.netcore.app.runtime.win-x64 5.0.3, 3.1.12. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet microsoft.netcore.app.runtime.mono.linux-arm: affected >= 5.0.0, < 5.0.3; fixed in 5.0.3
- NuGet microsoft.netcore.app.runtime.win-x86: affected >= 3.1.0, < 3.1.12; >= 5.0.0, < 5.0.3; fixed in 3.1.12, 5.0.3
- NuGet microsoft.netcore.app.runtime.mono.llvm.aot.linux-arm64: affected >= 5.0.0, < 5.0.3; fixed in 5.0.3
- NuGet microsoft.netcore.app.host.linux-arm64: affected >= 3.1.0, < 3.1.12; fixed in 3.1.12
- NuGet microsoft.netcore.app.runtime.android-x86: affected >= 5.0.0, < 5.0.3; fixed in 5.0.3
- NuGet microsoft.netcore.app.runtime.win-arm64: affected >= 3.1.0, < 3.1.12; >= 5.0.0, < 5.0.3; fixed in 3.1.12, 5.0.3
- NuGet microsoft.netcore.app.host.win-x86: affected >= 3.1.0, < 3.1.12; fixed in 3.1.12
- NuGet microsoft.netcore.app.host.linux-arm: affected >= 3.1.0, < 3.1.12; fixed in 3.1.12
- NuGet microsoft.netcore.app.runtime.mono.linux-arm64: affected >= 5.0.0, < 5.0.3; fixed in 5.0.3
- NuGet microsoft.netcore.app.runtime.ios-x86: affected >= 5.0.0, < 5.0.3; fixed in 5.0.3
- NuGet microsoft.netcore.app.runtime.linux-musl-x64: affected >= 3.1.0, < 3.1.12; >= 5.0.0, < 5.0.3; fixed in 3.1.12, 5.0.3
- NuGet microsoft.netcore.app.host.linux-musl-arm64: affected >= 3.1.0, < 3.1.12; fixed in 3.1.12
- NuGet microsoft.netcore.app.host.rhel.6-x64: affected >= 3.1.0, < 3.1.12; fixed in 3.1.12
- NuGet microsoft.netcore.app.host.win-x64: affected >= 3.1.0, < 3.1.12; fixed in 3.1.12
- NuGet microsoft.netcore.app.runtime.tvos-arm64: affected >= 5.0.0, < 5.0.3; fixed in 5.0.3
- NuGet microsoft.netcore.app.host.osx-x64: affected >= 3.1.0, < 3.1.12; fixed in 3.1.12
- NuGet microsoft.netcore.app.runtime.mono.linux-musl-x64: affected >= 5.0.0, < 5.0.3; fixed in 5.0.3
- NuGet microsoft.netcore.app.host.linux-x64: affected >= 3.1.0, < 3.1.12; fixed in 3.1.12
- NuGet microsoft.netcore.app.runtime.linux-arm64: affected >= 3.1.0, < 3.1.12; >= 5.0.0, < 5.0.3; fixed in 3.1.12, 5.0.3
- NuGet microsoft.netcore.app.runtime.mono.llvm.linux-arm64: affected >= 5.0.0, < 5.0.3; fixed in 5.0.3
- NuGet microsoft.netcore.app.runtime.mono.linux-x64: affected >= 5.0.0, < 5.0.3; fixed in 5.0.3
- NuGet microsoft.netcore.app.runtime.linux-arm: affected >= 3.1.0, < 3.1.12; >= 5.0.0, < 5.0.3; fixed in 3.1.12, 5.0.3
- NuGet microsoft.netcore.app.runtime.osx-x64: affected >= 3.1.0, < 3.1.12; >= 5.0.0, < 5.0.3; fixed in 3.1.12, 5.0.3
- NuGet microsoft.netcore.app.runtime.browser-wasm: affected >= 5.0.0, < 5.0.3; fixed in 5.0.3
- NuGet microsoft.netcore.app.host.win-arm: affected >= 3.1.0, < 3.1.12; fixed in 3.1.12
- NuGet microsoft.netcore.app.runtime.android-arm64: affected >= 5.0.0, < 5.0.3; fixed in 5.0.3
- NuGet microsoft.netcore.app.runtime.mono.llvm.linux-x64: affected >= 5.0.0, < 5.0.3; fixed in 5.0.3
- NuGet microsoft.netcore.app.runtime.mono.llvm.aot.osx-x64: affected >= 5.0.0, < 5.0.3; fixed in 5.0.3
- NuGet microsoft.netcore.app.runtime.linux-x64: affected >= 3.1.0, < 3.1.12; >= 5.0.0, < 5.0.3; fixed in 3.1.12, 5.0.3
- NuGet microsoft.netcore.app.runtime.android-x64: affected >= 5.0.0, < 5.0.3; fixed in 5.0.3
- NuGet microsoft.netcore.app.host.win-arm64: affected >= 3.1.0, < 3.1.12; fixed in 3.1.12
- NuGet microsoft.netcore.app.runtime.tvos-x64: affected >= 5.0.0, < 5.0.3; fixed in 5.0.3
- NuGet microsoft.netcore.app.runtime.ios-arm: affected >= 5.0.0, < 5.0.3; fixed in 5.0.3
- NuGet microsoft.netcore.app.runtime.mono.llvm.aot.linux-x64: affected >= 5.0.0, < 5.0.3; fixed in 5.0.3
- NuGet microsoft.netcore.app.runtime.ios-x64: affected >= 5.0.0, < 5.0.3; fixed in 5.0.3
- NuGet microsoft.netcore.app.runtime.linux-musl-arm: affected >= 5.0.0, < 5.0.3; fixed in 5.0.3
- NuGet microsoft.netcore.app.runtime.mono.osx-x64: affected >= 5.0.0, < 5.0.3; fixed in 5.0.3
- NuGet microsoft.netcore.app: affected >= 2.1.0, < 2.1.25; fixed in 2.1.25
- NuGet microsoft.netcore.app.host.linux-musl-x64: affected >= 3.1.0, < 3.1.12; fixed in 3.1.12
- NuGet microsoft.netcore.app.runtime.win-arm: affected >= 3.1.0, < 3.1.12; >= 5.0.0, < 5.0.3; fixed in 3.1.12, 5.0.3
- NuGet microsoft.netcore.app.runtime.mono.llvm.osx-x64: affected >= 5.0.0, < 5.0.3; fixed in 5.0.3
- NuGet microsoft.netcore.app.runtime.rhel.6-x64: affected >= 3.1.0, < 3.1.12; fixed in 3.1.12
- NuGet microsoft.netcore.app.runtime.linux-musl-arm64: affected >= 3.1.0, < 3.1.12; >= 5.0.0, < 5.0.3; fixed in 3.1.12, 5.0.3
- NuGet microsoft.netcore.app.runtime.android-arm: affected >= 5.0.0, < 5.0.3; fixed in 5.0.3
- NuGet microsoft.netcore.app.runtime.win-x64: affected >= 3.1.0, < 3.1.12; >= 5.0.0, < 5.0.3; fixed in 3.1.12, 5.0.3

## Suggested inspection (read-only)
- NuGet microsoft.netcore.app.runtime.mono.linux-arm: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.win-x86: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.mono.llvm.aot.linux-arm64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.host.linux-arm64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.android-x86: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.win-arm64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.host.win-x86: check the installed version with your package manager.
- NuGet microsoft.netcore.app.host.linux-arm: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.mono.linux-arm64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.ios-x86: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.linux-musl-x64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.host.linux-musl-arm64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.host.rhel.6-x64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.host.win-x64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.tvos-arm64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.host.osx-x64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.mono.linux-musl-x64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.host.linux-x64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.linux-arm64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.mono.llvm.linux-arm64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.mono.linux-x64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.linux-arm: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.osx-x64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.browser-wasm: check the installed version with your package manager.
- NuGet microsoft.netcore.app.host.win-arm: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.android-arm64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.mono.llvm.linux-x64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.mono.llvm.aot.osx-x64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.linux-x64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.android-x64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.host.win-arm64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.tvos-x64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.ios-arm: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.mono.llvm.aot.linux-x64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.ios-x64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.linux-musl-arm: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.mono.osx-x64: check the installed version with your package manager.
- NuGet microsoft.netcore.app: check the installed version with your package manager.
- NuGet microsoft.netcore.app.host.linux-musl-x64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.win-arm: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.mono.llvm.osx-x64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.rhel.6-x64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.linux-musl-arm64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.android-arm: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.win-x64: 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.netcore.app.runtime.mono.linux-arm, microsoft.netcore.app.runtime.win-x86, microsoft.netcore.app.runtime.mono.llvm.aot.linux-arm64, microsoft.netcore.app.host.linux-arm64, microsoft.netcore.app.runtime.android-x86, microsoft.netcore.app.runtime.win-arm64, microsoft.netcore.app.host.win-x86, microsoft.netcore.app.host.linux-arm, microsoft.netcore.app.runtime.mono.linux-arm64, microsoft.netcore.app.runtime.ios-x86, microsoft.netcore.app.runtime.linux-musl-x64, microsoft.netcore.app.host.linux-musl-arm64, microsoft.netcore.app.host.rhel.6-x64, microsoft.netcore.app.host.win-x64, microsoft.netcore.app.runtime.tvos-arm64, microsoft.netcore.app.host.osx-x64, microsoft.netcore.app.runtime.mono.linux-musl-x64, microsoft.netcore.app.host.linux-x64, microsoft.netcore.app.runtime.linux-arm64, microsoft.netcore.app.runtime.mono.llvm.linux-arm64, microsoft.netcore.app.runtime.mono.linux-x64, microsoft.netcore.app.runtime.linux-arm, microsoft.netcore.app.runtime.osx-x64, microsoft.netcore.app.runtime.browser-wasm, microsoft.netcore.app.host.win-arm, microsoft.netcore.app.runtime.android-arm64, microsoft.netcore.app.runtime.mono.llvm.linux-x64, microsoft.netcore.app.runtime.mono.llvm.aot.osx-x64, microsoft.netcore.app.runtime.linux-x64, microsoft.netcore.app.runtime.android-x64, microsoft.netcore.app.host.win-arm64, microsoft.netcore.app.runtime.tvos-x64, microsoft.netcore.app.runtime.ios-arm, microsoft.netcore.app.runtime.mono.llvm.aot.linux-x64, microsoft.netcore.app.runtime.ios-x64, microsoft.netcore.app.runtime.linux-musl-arm, microsoft.netcore.app.runtime.mono.osx-x64, microsoft.netcore.app, microsoft.netcore.app.host.linux-musl-x64, microsoft.netcore.app.runtime.win-arm, microsoft.netcore.app.runtime.mono.llvm.osx-x64, microsoft.netcore.app.runtime.rhel.6-x64, microsoft.netcore.app.runtime.linux-musl-arm64, microsoft.netcore.app.runtime.android-arm, microsoft.netcore.app.runtime.win-x64.
- 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-3gp9-h8hw-pxpw (GitHub-reviewed advisory GHSA-3gp9-h8hw-pxpw lists affected ranges: NuGet microsoft.netcore.app >=2.1.0 =3.1.0 =3.1.0 =3.1.0 =3.1.0 =3.1.0 =3.1.0 <3.1.12; NuGet…)

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