IMPORTANT Windows 8.1 and Windows Server 2012 R2 have reached the end of mainstream support and are now in extended support. Starting in July 2020, there will no longer be optional, non-security releases (known as "C" releases) for this operating system. Operating systems in extended support have only cumulative monthly security updates (known as the "B" or Update Tuesday release).
For more information about the various types of Windows updates, such as critical, security, driver, service packs, and so on, please see the following article. To view other notes and messages, see the Windows 8.1 and Windows Server 2012 R2 update history home page.
This security update includes quality improvements. Key changes include:
For more information about the resolved security vulnerabilities, please refer to the new Security Update Guide website.
Certain operations, such as rename , that you perform on files or folders that are on a Cluster Shared Volume (CSV) may fail with the error, “STATUS_BAD_IMPERSONATION_LEVEL (0xC00000A5)”. This occurs when you perform the operation on a CSV owner node from a process that doesn’t have administrator privilege.| Do one of the following:
Microsoft is working on a resolution and will provide an update in an upcoming
After installing this update on domain controllers (DCs) and read-only domain controllers (RODCs) in your environment, you might encounter Kerberos authentication and ticket renewal issues. This is caused by an issue in how CVE-2020-17049 was addressed in these updates.For specific symptoms and behaviors related to this issue, please see the Windows release health page. Note This issue only affects Windows Servers, Windows 10 devices and applications in enterprise environments.| This issue is resolved in KB4594439.
Before installing this update We strongly recommend that you install the latest servicing stack update (SSU) for your operating system before you install the latest Rollup. SSUs improve the reliability of the update process to mitigate potential issues while installing the Rollup and applying Microsoft security fixes. For general information about SSUs, see Servicing stack updates and Servicing Stack Updates (SSU): Frequently Asked Questions.If you use Windows Update, the latest SSU (KB4566425) will be offered to you automatically. To get the standalone package for the latest SSU, search for it in the Microsoft Update Catalog.
REMINDER If you are using Security-only updates, you will also need to install all previous Security-only updates and the latest cumulative update for Internet Explorer (KB4586768).
Install this update Release Channel| Available| Next Step
Windows Update and Microsoft Update| No| See the other options below.
Microsoft Update Catalog| Yes| To get the standalone package for this update, go to the Microsoft Update Catalog website.
Windows Server Update Services (WSUS)| Yes| This update will automatically sync with WSUS if you configure Products and Classifications as follows: Product : Windows 8.1, Windows Server 2012 R2, Windows Embedded 8.1 Industry Enterprise, Windows Embedded 8.1 Industry Pro Classification : Security Updates
File information For a list of the files that are provided in this update, download the file information for update 4586823.