CVE-2026-66822: Insertion of sensitive information into sent data in .NET allows an unauthorized attacker to disclose information over a network.

CVE-2026-66822 · Severity: medium · CVSS 5.9 · Published 2026-10-13

.NET is a runtime framework that executes applications written in C# and other .NET languages on Windows, Linux, and macOS. The SocketsHttpHandler component can leak basic proxy authentication credentials to a destination server when following HTTP redirects, allowing an attacker who controls an intermediate proxy or redirect chain to capture plaintext credentials. An attacker would need to position themselves in the network path or control a redirect target to exploit this.

Technologies: Microsoft .Net, 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), Microsoft.NetCore.App.Runtime.win-arm64 (NuGet), Microsoft.NetCore.App.Runtime.win-x64 (NuGet), Microsoft.NetCore.App.Runtime.win-x86 (NuGet). Vendors: Microsoft, NuGet.

Quick answers

Is CVE-2026-66822 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-66822 being exploited in the wild.
How severe is CVE-2026-66822?
Medium severity, with a CVSS score of 5.9, published 13 October 2026.
Which products and versions are affected?
Microsoft .Net 8.0.0-8.0.31, 9.0.0-9.0.20, 10.0.0-10.0.12, 11.0.0-preview.1 to 11.0.0-rc.1; Microsoft.NetCore.App.Runtime.linux-arm (NuGet) >= 9.0.0, <= 9.0.20, ECOSYSTEM:introduced=9.0.0,fixed=9.0.21; Microsoft.NetCore.App.Runtime.linux-arm64 (NuGet) >= 9.0.0, <= 9.0.20, ECOSYSTEM:introduced=9.0.0,fixed=9.0.21; Microsoft.NetCore.App.Runtime.linux-musl-arm (NuGet) >= 9.0.0, <= 9.0.20, ECOSYSTEM:introduced=9.0.0,fixed=9.0.21; and 8 more.
Is there a fix for CVE-2026-66822?
Yes. Microsoft.NetCore.App.Runtime.linux-arm (NuGet): upgrade to 9.0.21 or later; Microsoft.NetCore.App.Runtime.linux-arm64 (NuGet): upgrade to 9.0.21 or later; Microsoft.NetCore.App.Runtime.linux-musl-arm (NuGet): upgrade to 9.0.21 or later; Microsoft.NetCore.App.Runtime.linux-musl-arm64 (NuGet): upgrade to 9.0.21 or later; Microsoft.NetCore.App.Runtime.linux-musl-x64 (NuGet): upgrade to 9.0.21 or later; Microsoft.NetCore.App.Runtime.linux-x64 (NuGet): upgrade to 9.0.21 or later; Microsoft.NetCore.App.Runtime.osx-arm64 (NuGet): upgrade to 9.0.21 or later; Microsoft.NetCore.App.Runtime.osx-x64 (NuGet): upgrade to 9.0.21 or later; Microsoft.NetCore.App.Runtime.win-arm64 (NuGet): upgrade to 9.0.21 or later; Microsoft.NetCore.App.Runtime.win-x64 (NuGet): upgrade to 9.0.21 or later; Microsoft.NetCore.App.Runtime.win-x86 (NuGet): upgrade to 9.0.21 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-66822 attacked?
It is attacked over the network.
Am I affected by CVE-2026-66822?
Check whether you run Microsoft .Net, Microsoft.NetCore.App.Runtime.linux-arm (NuGet), Microsoft.NetCore.App.Runtime.linux-arm64 (NuGet) 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 9.0.21 or later
    dotnet add package Microsoft.NetCore.App.Runtime.linux-arm --version 9.0.21
  • Microsoft.NetCore.App.Runtime.linux-arm64 (NuGet): upgrade to 9.0.21 or later
    dotnet add package Microsoft.NetCore.App.Runtime.linux-arm64 --version 9.0.21
  • Microsoft.NetCore.App.Runtime.linux-musl-arm (NuGet): upgrade to 9.0.21 or later
    dotnet add package Microsoft.NetCore.App.Runtime.linux-musl-arm --version 9.0.21
  • Microsoft.NetCore.App.Runtime.linux-musl-arm64 (NuGet): upgrade to 9.0.21 or later
    dotnet add package Microsoft.NetCore.App.Runtime.linux-musl-arm64 --version 9.0.21
  • Microsoft.NetCore.App.Runtime.linux-musl-x64 (NuGet): upgrade to 9.0.21 or later
    dotnet add package Microsoft.NetCore.App.Runtime.linux-musl-x64 --version 9.0.21
  • Microsoft.NetCore.App.Runtime.linux-x64 (NuGet): upgrade to 9.0.21 or later
    dotnet add package Microsoft.NetCore.App.Runtime.linux-x64 --version 9.0.21
  • Microsoft.NetCore.App.Runtime.osx-arm64 (NuGet): upgrade to 9.0.21 or later
    dotnet add package Microsoft.NetCore.App.Runtime.osx-arm64 --version 9.0.21
  • Microsoft.NetCore.App.Runtime.osx-x64 (NuGet): upgrade to 9.0.21 or later
    dotnet add package Microsoft.NetCore.App.Runtime.osx-x64 --version 9.0.21
  • Microsoft.NetCore.App.Runtime.win-arm64 (NuGet): upgrade to 9.0.21 or later
    dotnet add package Microsoft.NetCore.App.Runtime.win-arm64 --version 9.0.21
  • Microsoft.NetCore.App.Runtime.win-x64 (NuGet): upgrade to 9.0.21 or later
    dotnet add package Microsoft.NetCore.App.Runtime.win-x64 --version 9.0.21
  • Microsoft.NetCore.App.Runtime.win-x86 (NuGet): upgrade to 9.0.21 or later
    dotnet add package Microsoft.NetCore.App.Runtime.win-x86 --version 9.0.21

Technical details

The vulnerability is an information disclosure (CWE-201) in System.Net.Http where SocketsHttpHandler retains the Proxy-Authorization header across HTTP redirects. An attacker positioned to control an intermediate HTTP redirect response can trick an application into sending proxy credentials to an attacker-controlled destination server. The attack requires network access to intercept or inject a redirect but no user interaction or prior authentication.

Affected products

  • Microsoft .NET 8.0.0-8.0.31, 9.0.0-9.0.20, 10.0.0-10.0.12, 11.0.0-preview.1 to 11.0.0-rc.1

Identifiers

  • CVE-2026-66822
  • GHSA-wxxw-5cvc-53j7

Timeline

  • 2026-10-13: disclosed

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