CVE-2021-26423 .NET Core and Visual Studio Denial of Service Vulnerability
High 7.5
Published
Updated
Check this codebase for CVE-2021-26423 and fix it if it is affected.
What it is: CVE-2021-26423 is a high-severity denial of service vulnerability in Microsoft .Net, published on 12 Aug 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-26423 in the wild and no public exploit code.
Affected packages and fixed versions:
- Microsoft.NETCore.App.Runtime.linux-arm (NuGet): affected from 3.1.0; fixed in 3.1.18
- Microsoft.NETCore.App.Runtime.linux-arm (NuGet): affected from 3.1.0; fixed in 3.1.18
- Microsoft.NETCore.App.Runtime.linux-arm (NuGet): affected from 5.0.0; fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.linux-arm (NuGet): affected from 5.0.0; fixed in 5.0.9
- dotnet (Bitnami): affected from 5.0.0; fixed in 5.0.9
- dotnet-sdk (Bitnami): affected from 5.0.0; fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.Mono.LLVM.AOT.linux-arm64 (NuGet): affected from 5.0.0; fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.Mono.LLVM.AOT.linux-arm64 (NuGet): affected from 5.0.0; fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.Mono.LLVM.AOT.linux-x64 (NuGet): affected from 5.0.0; fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.Mono.LLVM.AOT.linux-x64 (NuGet): affected from 5.0.0; fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.Mono.LLVM.AOT.osx-x64 (NuGet): affected from 5.0.0; fixed in 5.0.9
- Microsoft.NETCore.App.Runtime.Mono.LLVM.AOT.osx-x64 (NuGet): affected from 5.0.0; fixed in 5.0.9
Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.
Reference: https://insights.sbomify.com/CVE-2021-26423/ (Markdown: https://insights.sbomify.com/CVE-2021-26423/index.md)
Attackers can cause a denial of service in .NET Core and Visual Studio environments, requiring users to apply vendor patches.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2021-26423?
CVE-2021-26423 is a high-severity denial of service vulnerability in Microsoft .Net, published on 12 Aug 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
.NET Core and Visual Studio Denial of Service Vulnerability
Which versions are affected by CVE-2021-26423?
40 open source packages ship an affected version, including Microsoft.NETCore.App.Runtime.linux-arm, dotnet and dotnet-sdk. It affects 5 products.
| Package | Affected | Fixed in |
|---|---|---|
Microsoft.NETCore.App.Runtime.linux-arm NuGet | From 3.1.0 | 3.1.18 |
Microsoft.NETCore.App.Runtime.linux-arm NuGet | From 3.1.0 | 3.1.18 |
Microsoft.NETCore.App.Runtime.linux-arm NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.linux-arm NuGet | From 5.0.0 | 5.0.9 |
dotnet Bitnami | From 5.0.0 | 5.0.9 |
dotnet-sdk Bitnami | From 5.0.0 | 5.0.9 |
34 more packages
Microsoft.NETCore.App.Runtime.Mono.LLVM.AOT.linux-arm64 NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.Mono.LLVM.AOT.linux-arm64 NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.Mono.LLVM.AOT.linux-x64 NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.Mono.LLVM.AOT.linux-x64 NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.Mono.LLVM.AOT.osx-x64 NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.Mono.LLVM.AOT.osx-x64 NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.Mono.LLVM.linux-arm64 NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.Mono.LLVM.linux-arm64 NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.Mono.LLVM.linux-x64 NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.Mono.LLVM.linux-x64 NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.Mono.LLVM.osx-x64 NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.Mono.LLVM.osx-x64 NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.Mono.linux-arm NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.Mono.linux-arm NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.Mono.linux-arm64 NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.Mono.linux-arm64 NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.Mono.linux-musl-x64 NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.Mono.linux-musl-x64 NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.Mono.linux-x64 NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.Mono.linux-x64 NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.Mono.osx-x64 NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.Mono.osx-x64 NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.linux-arm64 NuGet | From 3.1.0 | 3.1.18 |
Microsoft.NETCore.App.Runtime.linux-arm64 NuGet | From 3.1.0 | 3.1.18 |
Microsoft.NETCore.App.Runtime.linux-arm64 NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.linux-arm64 NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.linux-musl-arm NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.linux-musl-arm NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.linux-musl-arm64 NuGet | From 3.1.0 | 3.1.18 |
Microsoft.NETCore.App.Runtime.linux-musl-arm64 NuGet | From 3.1.0 | 3.1.18 |
Microsoft.NETCore.App.Runtime.linux-musl-arm64 NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.linux-musl-arm64 NuGet | From 5.0.0 | 5.0.9 |
Microsoft.NETCore.App.Runtime.linux-musl-x64 NuGet | From 3.1.0 | 3.1.18 |
Microsoft.NETCore.App.Runtime.linux-musl-x64 NuGet | From 3.1.0 | 3.1.18 |
Products include Microsoft .Net, Microsoft .Net Core, Microsoft Powershell Core, Microsoft Visual Studio 2017, Microsoft Visual Studio 2019.
How do I fix CVE-2021-26423?
Upgrade Microsoft.NETCore.App.Runtime.linux-arm to a fixed version for your release line: 3.1.18 or 5.0.9.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2021-26423 being exploited?
There is no known exploitation of CVE-2021-26423 in the wild and no public exploit code.
Other vulnerabilities in Microsoft .Net
- CVE-2024-43498 .NET and Visual Studio Remote Code Execution Vulnerability
- CVE-2024-0057 NET, .NET Framework, and Visual Studio Security Feature Bypass Vulnerability
- CVE-2026-96957 .NET Security Feature Bypass Vulnerability
- CVE-2026-69439 .NET and Visual Studio Elevation of Privilege Vulnerability
- CVE-2026-71328 .NET and Visual Studio Remote Code Execution Vulnerability
Sources
Also known as BIT-dotnet-2021-26423, BIT-dotnet-sdk-2021-26423, GHSA-rh58-r7jh-xhx3.