September 16, 2020-KB4576947 Cumulative Update Preview for .NET Framework 3.5 and 4.8 for Windows 10, version 1903, Windows Server, version 1903, Windows 10, version 1909 and Windows Server, version 1909

Applies to: .NET Framework

The September 16, 2020 update for Windows 10, version 1903, Windows Server, version 1903, Windows 10, version 1909 and Windows Server, version 1909 includes cumulative reliability improvements in .NET Framework 3.5 and 4.8. We recommend that you apply this update as part of your regular maintenance routines. Before you install this update, see the Prerequisites and Restart requirement sections.

Quality and reliability improvements


WCF1

- Addressed an issue with WCF services sometimes failing to start when starting multiple services concurrently.

Winforms

- Addressed a regression introduced in .NET Framework 4.8, where Control.AccessibleName, Control.AccessibleRole, and Control.AccessibleDescription properties stopped working for the following controls:Label, GroupBox, ToolStrip, ToolStripItems, StatusStrip, StatusStripItems, PropertyGrid, ProgressBar, ComboBox, MenuStrip, MenuItems, DataGridView.

- Addressed a regression in accessible name for combo box items for data bound combo boxes. .NET Framework 4.8 started using type name instead of the value of the DisplayMember property as an accessible name, this improvement uses the DisplayMember again.

ASP.NET

- Disabled resuse of AppPathModifier in ASP.Net control output.

- HttpCookie objects in the ASP.Net request context will be created with configured defaults for cookie flags instead of .NET-style primitive defaults to match the behavior of `new HttpCookie(name)`.

SQL

- Addressed a failure that sometimes occured when a user connects to one Azure SQL database, performed an enclave based operation, and then connected to another database under the same server that has the same Attestation URL and performed an enclave operation on the second server.

CLR2

- Added a CLR config variable Thread_AssignCpuGroups (1 by default) that can be set to 0 to disable automatic CPU group assignment done by the CLR for new threads created by Thread.Start() and thread pool threads, such that an app may do its own thread-spreading.

- Addressed a rare data corruption that can occur when using new API’s such as Unsafe.ByteOffset<T> which are often used with the new Span types. The corruption could occur when a GC operation is performed while a thread is calling Unsafe.ByteOffset<T> from inside of a loop.

- Addressed an issue regarding timers with very long due times ticking down much sooner than expected when the AppContext switch "Switch.System.Threading.UseNetCoreTimer" is enabled.


1 Windows Communication Foundation (WCF)
2 Common Language Runtime (CLR)

Known issues in this security update


Symptoms
After you apply this September 16, 2020 Security and Quality Rollup for .NET Framework 4.8, some ASP.Net applications fail during precompilation. The error message that you receive will likely contain the words “Error ASPCONFIG.”

Cause
An invalid configuration state in either the “sessionState,” “anonymouseIdentification,” or “authentication/forms” sections of “System.web” configuration. This might occur during build-and-publish routines if configuration transformations leave the Web.config file in an intermediate state for precompilation.

Workaround
Customers who observe new unexpected failures or functional issues can implement an application setting by adding (or merging) the following code to the application configuration file. Setting either “true” or “false” will avoid the issue. However, we recommend that you set this value to “true” for sites that do not rely on cookieless features.

<?xml version="1.0" encoding="utf-8" ?><configuration>      <appSettings>          <add key=”aspnet:DisableAppPathModifier” value=”true” />     </appSettings></configuration>

How to obtain and install the update


Install this update

Release Channel Available Next Step
Windows Update and Microsoft Update Yes

To download and install this update, go to Settings > Update & Security > Windows Update, and then select Check for updates.

Microsoft Update Catalog Yes To get the standalone package for this update, go to the Microsoft Update Catalog website.
Windows Server Update Services (WSUS) No

You can import this update into WSUS manually. See the Microsoft Update Catalog for instructions.

File information

For a list of the files that are provided in this update, download the file information for cumulative update .

Prerequisites

To apply this update, you must have .NET Framework 3.5 or 4.8 installed.

Restart requirement

You must restart the computer after you apply this update if any affected files are being used. We recommend that you exit all .NET Framework-based applications before you apply this update.

How to obtain help and support for this update