CVE-2026-62899: Microsoft .NET security feature bypass in System.Net.HttpListener

CVE-2026-62899 · Severity: medium · CVSS 5.9 · Published 2026-08-11

A security vulnerability exists in the Microsoft .NET component used for handling web requests (HttpListener) on Linux and macOS. This flaw could allow an unauthorized attacker to bypass security protections by sending specially crafted web traffic. If exploited, this could lead to unauthorized access to sensitive information or the ability to circumvent intended security controls within the application.

Technologies: Apple macOS, Linux Kernel, Microsoft .Net, Microsoft Visual Studio 2022, Microsoft Visual Studio 2026, Microsoft Windows, Microsoft.NetCore.App.Runtime.linux-arm (NuGet), Microsoft.NetCore.App.Runtime.linux-arm64 (NuGet), Microsoft.NetCore.App.Runtime.linux-musl-arm (NuGet), Microsoft.NetCore.App.Runtime.linux-musl-arm64 (NuGet), Microsoft.NetCore.App.Runtime.linux-musl-x64 (NuGet), Microsoft.NetCore.App.Runtime.linux-x64 (NuGet), Microsoft.NetCore.App.Runtime.osx-arm64 (NuGet), Microsoft.NetCore.App.Runtime.osx-x64 (NuGet). Vendors: Apple, Linux, Microsoft, NuGet.

Quick answers

Is CVE-2026-62899 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-62899 being exploited in the wild.
How severe is CVE-2026-62899?
Medium severity, with a CVSS score of 5.9, published 11 August 2026.
Which products and versions are affected?
Microsoft.NetCore.App.Runtime.linux-arm (NuGet) ECOSYSTEM:introduced=10.0.0,fixed=10.0.11; Microsoft.NetCore.App.Runtime.linux-arm64 (NuGet) ECOSYSTEM:introduced=10.0.0,fixed=10.0.11; Microsoft.NetCore.App.Runtime.linux-musl-arm (NuGet) ECOSYSTEM:introduced=10.0.0,fixed=10.0.11; Microsoft.NetCore.App.Runtime.linux-musl-arm64 (NuGet) ECOSYSTEM:introduced=10.0.0,fixed=10.0.11; and 4 more.
Is there a fix for CVE-2026-62899?
Yes. Microsoft.NetCore.App.Runtime.linux-arm (NuGet): upgrade to 10.0.11 or later; Microsoft.NetCore.App.Runtime.linux-arm64 (NuGet): upgrade to 10.0.11 or later; Microsoft.NetCore.App.Runtime.linux-musl-arm (NuGet): upgrade to 10.0.11 or later; Microsoft.NetCore.App.Runtime.linux-musl-arm64 (NuGet): upgrade to 10.0.11 or later; Microsoft.NetCore.App.Runtime.linux-musl-x64 (NuGet): upgrade to 10.0.11 or later; Microsoft.NetCore.App.Runtime.linux-x64 (NuGet): upgrade to 10.0.11 or later; Microsoft.NetCore.App.Runtime.osx-arm64 (NuGet): upgrade to 10.0.11 or later; Microsoft.NetCore.App.Runtime.osx-x64 (NuGet): upgrade to 10.0.11 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-62899 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-62899?
Check whether you run Apple macOS, Linux Kernel, Microsoft .Net or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • Microsoft.NetCore.App.Runtime.linux-arm (NuGet): upgrade to 10.0.11 or later
    dotnet add package Microsoft.NetCore.App.Runtime.linux-arm --version 10.0.11
  • Microsoft.NetCore.App.Runtime.linux-arm64 (NuGet): upgrade to 10.0.11 or later
    dotnet add package Microsoft.NetCore.App.Runtime.linux-arm64 --version 10.0.11
  • Microsoft.NetCore.App.Runtime.linux-musl-arm (NuGet): upgrade to 10.0.11 or later
    dotnet add package Microsoft.NetCore.App.Runtime.linux-musl-arm --version 10.0.11
  • Microsoft.NetCore.App.Runtime.linux-musl-arm64 (NuGet): upgrade to 10.0.11 or later
    dotnet add package Microsoft.NetCore.App.Runtime.linux-musl-arm64 --version 10.0.11
  • Microsoft.NetCore.App.Runtime.linux-musl-x64 (NuGet): upgrade to 10.0.11 or later
    dotnet add package Microsoft.NetCore.App.Runtime.linux-musl-x64 --version 10.0.11
  • Microsoft.NetCore.App.Runtime.linux-x64 (NuGet): upgrade to 10.0.11 or later
    dotnet add package Microsoft.NetCore.App.Runtime.linux-x64 --version 10.0.11
  • Microsoft.NetCore.App.Runtime.osx-arm64 (NuGet): upgrade to 10.0.11 or later
    dotnet add package Microsoft.NetCore.App.Runtime.osx-arm64 --version 10.0.11
  • Microsoft.NetCore.App.Runtime.osx-x64 (NuGet): upgrade to 10.0.11 or later
    dotnet add package Microsoft.NetCore.App.Runtime.osx-x64 --version 10.0.11

Technical details

A vulnerability classified as HTTP Request/Response Smuggling (CWE-444) exists in the System.Net.HttpListener component of Microsoft .NET when running on Linux and macOS. The root cause is an inconsistent interpretation of HTTP requests, which allows an unauthenticated attacker to bypass security features over the network. Exploitation requires a specific environment configuration (high attack complexity) but can result in a loss of confidentiality. Patches are available in .NET versions 8.0.30, 9.0.19, and 10.0.11. Developers using self-contained deployments must recompile and redeploy their applications to apply the fix.

Affected products

  • Microsoft .NET 8.0.0 - 8.0.29, 9.0.0 - 9.0.18, 10.0.0 - 10.0.10

Identifiers

  • CVE-2026-62899
  • GHSA-r6mh-95jw-g7qg

Timeline

  • 2026-08-11: advisory: Advisory published by Microsoft and GitHub
  • 2026-08-11: patched

References

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