January 3, 2018—KB4056891 (OS Build 15063.850)

Improvements and fixes

This update includes quality improvements. No new operating system features are being introduced in this update. Key changes include:

Security updates to Internet Explorer, Microsoft Scripting Engine, Microsoft Edge, Windows Graphics, Windows Kernel, Windows Subsystem for Linux, and the Windows SMB Server.

If you installed earlier updates, only the new fixes contained in this package will be downloaded and installed on your device.

For more information about the resolved security vulnerabilities, see the Security Update Guide.

Known issues in this update

Symptom	Workaround
When calling CoInitializeSecurity, the call will fail if passing RPC_C_IMP_LEVEL_NONE under certain conditions. When calling CoInitializeSecurity, the call may fail when passing RPC_C_AUTHN_LEVEL_NONE as the authentication level. The error returned on failure is STATUS_BAD_IMPERSONATION_LEVEL.	This issue is resolved in KB4057144.
Because of an issue that affects some versions of antivirus software, this fix applies only to computers on which the antivirus ISV updated the ALLOW REGKEY.	This issue is resolved in KB4088782.
Microsoft has reports of some customers on a small subset of older AMD processors getting into an unbootable state after installing this KB. To prevent this issue, Microsoft will temporarily pause Windows OS updates to devices with impacted AMD processors at this time.	This issue is resolved in KB 4057144.
After installing this update, some users may experience issues logging into some websites when using third-party account credentials in Microsoft Edge.	This issue is resolved in KB4074592.

How to get this update

This update will be downloaded and installed automatically from Windows Update. To get the standalone package for this update, go to the Microsoft Update Catalog website.

File information

For a list of the files that are provided in this update, download the file information for cumulative update 4056891.