February 27, 2020-KB4537572 Cumulative Update for .NET Framework 3.5 and 4.8 for Windows 10 Version 1903 and Windows Server 1903 RTM and Windows 10, version 1909 and Windows Server, version 1909

CLR¹

- Addresses an issue with rare crashes or deadlocks that could occur if a GC occurs while another thread is running NGen'ed code which makes the initial call into a static method within the same module where one or more parameter types involve type-forwarded value types.

- Addresses rare crashes that could occur if Server GC is enabled and a GC occurs while another thread is running NGen'ed code which is making the initial call into NGen'ed code in a 2nd module where one or more parameter types involve valuetypes defined in a 3rd module.

- Addresses an issue with a crash that could occur in some configurations involving either hot-added CPUs or multi-group machines where per-group CPU count is not consistent across all groups.

- Addresses an issue with a rare crash that can occur during the first call that native code makes into the managed portion of a mixed-mode DLL.

Workflow

- Addresses an accessibility issue where text inside a Windows Workflow Foundation Visual Basic Editor would use the wrong colors in high contrast themes.

Winforms

- Addresses an issue with interaction between WPF user control and hosting WinForms app when processing keyboard input.

- Addresses an issue getting accessible objects for PropertyGridView ComboBox property items - adding the verification for item existence and validity.

- Addresses an issue with WinForms ComboBox control reinitialization in AD FS MMC UI.

WCF²

- Addresses an issue when using the WCFNetTcp binding. If a client stops responding during the connection handshake, sometimes a service will use the binding receive timeout instead of the open timeout. This update ensures that the correct open timeout is used during the entire handshake.