Today, we are releasing the December 2019 Security and Quality Rollup Updates for .NET Framework.

Security

No new security fixes. See September 2019 Security and Quality Rollup for the latest security updates.

Quality and Reliability

This release contains the following quality and reliability improvements.

ASP.NET

• ASP.NET will now emit a SameSite cookie header when HttpCookie.SameSite value is “None” to accommodate upcoming changes to SameSite cookie handling in Chrome. As part of this change, FormsAuth and SessionState cookies will also be issued with SameSite = ‘Lax’ instead of the previous default of ‘None’, though these values can be overridden in web.config. For more information, refer to Work with SameSite cookies in ASP.NET.

CLR¹

• Addresses an issue where some ClickOnce applications or applications creating the default AppDomain with a restricted permission set may observe application launch or application runtime failures, or unexpected behaviors. The observable issue was the System.AppDomainSetup.TargetFrameworkName is null, leading to any quirks enabling reverting back to .NET Framework 4.0 behaviors.

WPF²

• Addresses an issue where some Per-Monitor Aware WPF applications that host System-Aware or Unaware child-windows, and run on .NET 4.8, may occasionally encounter a crash with exceptionSystem.Collections.Generic.KeyNotFoundException.

¹ Common Language Runtime (CLR)
² Windows Presentation Foundation (WPF)

Known Issues in this update

There are no known issues with this update. This update includes improvements to resolve a known issue discussed in October Preview of Quality Rollup that occurs after applying the .NET Framework 4.8 patch. To resolve the known issue issue, install update for .NET Framework 4.8 available in this December 2019 Security and Quality Rollup.

Getting the Update

The Security and Quality Rollup is available via Windows Update, Windows Server Update Services, and Microsoft Update Catalog.

Microsoft Update Catalog

You can get the update via the Microsoft Update Catalog. For Windows 10, NET Framework 4.8 updates are available via Windows Update, Windows Server Update Services, Microsoft Update Catalog. Updates for other versions of .NET Framework are part of the Windows 10 Monthly Cumulative Update.

Note: Customers that rely on Windows Update and Windows Server Update Services will automatically receive the .NET Framework version-specific updates. Advanced system administrators can also take use of the below direct Microsoft Update Catalog download links to .NET Framework-specific updates. Before applying these updates, please ensure that you carefully review the .NET Framework version applicability, to ensure that you only install updates on systems where they apply.

The following table is for Windows 10 and Windows Server 2016+ versions.

The following table is for earlier Windows and Windows Server versions.

Previous Monthly Rollups

The last few .NET Framework Monthly updates are listed below for your convenience:
* November 2019 Preview of Quality Rollup
* October 2019 Preview of Quality Rollup
* October 2019 Security and Quality Rollup