CVE-2026-83520: .NET WindowsDesktop.App.Runtime XAML deserialization RCE

CVE-2026-83520 · Severity: high · CVSS 8.8 · Published 2026-10-13

Microsoft .NET's Windows Desktop runtime, which powers graphical applications built with WPF, contains a flaw in how it processes XAML markup that can allow remote code execution. An attacker can craft a malicious XAML file or navigate a user to a malicious website that triggers unsafe deserialization, leading to complete compromise of the affected application and system.

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

Quick answers

Is CVE-2026-83520 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-83520 being exploited in the wild.
How severe is CVE-2026-83520?
High severity, with a CVSS score of 8.8, published 13 October 2026.
Which products and versions are affected?
Microsoft .NET WindowsDesktop.App.Runtime 8.0.0 through 8.0.31, 9.0.0 through 9.0.20, 10.0.0 through 10.0.12, 11.0.0-preview.1 through 11.0.0-rc.1; Microsoft.WindowsDesktop.App.Runtime.win-arm64 (NuGet) >= 11.0.0-preview.1, <= 11.0.0-rc.1, ECOSYSTEM:introduced=11.0.0-preview.1,fixed=11.0.0-rc.2; Microsoft.WindowsDesktop.App.Runtime.win-x64 (NuGet) >= 11.0.0-preview.1, <= 11.0.0-rc.1, ECOSYSTEM:introduced=11.0.0-preview.1,fixed=11.0.0-rc.2; Microsoft.WindowsDesktop.App.Runtime.win-x86 (NuGet) >= 11.0.0-preview.1, <= 11.0.0-rc.1, ECOSYSTEM:introduced=11.0.0-preview.1,fixed=11.0.0-rc.2.
Is there a fix for CVE-2026-83520?
Yes. Microsoft.WindowsDesktop.App.Runtime.win-arm64 (NuGet): upgrade to 11.0.0-rc.2 or later; Microsoft.WindowsDesktop.App.Runtime.win-x64 (NuGet): upgrade to 11.0.0-rc.2 or later; Microsoft.WindowsDesktop.App.Runtime.win-x86 (NuGet): upgrade to 11.0.0-rc.2 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-83520 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-83520?
Check whether you run Microsoft .NET WindowsDesktop.App.Runtime, Microsoft.WindowsDesktop.App.Runtime.win-arm64 (NuGet), Microsoft.WindowsDesktop.App.Runtime.win-x64 (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.WindowsDesktop.App.Runtime.win-arm64 (NuGet): upgrade to 11.0.0-rc.2 or later
    dotnet add package Microsoft.WindowsDesktop.App.Runtime.win-arm64 --version 11.0.0-rc.2
  • Microsoft.WindowsDesktop.App.Runtime.win-x64 (NuGet): upgrade to 11.0.0-rc.2 or later
    dotnet add package Microsoft.WindowsDesktop.App.Runtime.win-x64 --version 11.0.0-rc.2
  • Microsoft.WindowsDesktop.App.Runtime.win-x86 (NuGet): upgrade to 11.0.0-rc.2 or later
    dotnet add package Microsoft.WindowsDesktop.App.Runtime.win-x86 --version 11.0.0-rc.2

Technical details

The vulnerability stems from deserialization of untrusted XAML and XPS data (CWE-502), where unsafe URI fetching, unrestricted hyperlink navigation, and unprotected TrueType font loading can be exploited. An attacker with network access can deliver a malicious XAML file or craft a navigation action requiring only user interaction (clicking a link). The fixes restrict URI fetching, add XAML nesting-depth limits, enable font protection, and prevent caching of untrusted DNS decisions.

Affected products

  • Microsoft .NET WindowsDesktop.App.Runtime 8.0.0 through 8.0.31, 9.0.0 through 9.0.20, 10.0.0 through 10.0.12, 11.0.0-preview.1 through 11.0.0-rc.1

Identifiers

  • CVE-2026-83520
  • GHSA-4w5f-7jp2-w48g

Timeline

  • 2026-10-13: disclosed

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