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April 13, 2021—KB5001337 (OS Build 18363.1500)

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None **NEW 4/13/21** **IMPORTANT **Windows 10, version 1909 will reach end of service on May 11, 2021 for devices running the Home, Pro, Pro for Workstation, Nano Container, and Server SAC editions. After May 11, 2021, these devices will no longer receive monthly security and quality updates that contain protection from the latest security threats. To continue receiving security and quality updates, Microsoft recommends updating to the latest version of Windows 10.We will continue to service the following editions: Enterprise, Education, and IoT Enterprise. **NEW 4/13/21 REMINDER **Microsoft removed the Microsoft Edge Legacy desktop application that is out of support in March 2021. In this April 13, 2021 release, we will install the new Microsoft Edge. For more information, see [New Microsoft Edge to replace Microsoft Edge Legacy with April’s Windows 10 Update Tuesday release](<https://aka.ms/EdgeLegacyEOS>). **2/16/21** **IMPORTANT **As part of the end of support for Adobe Flash, KB4577586 is now available as an optional update from Windows Update (WU) and Windows Server Update Services (WSUS). Installing KB4577586 will remove Adobe Flash Player permanently from your Windows device. Once installed, you cannot uninstall KB4577586. For more details about Microsoft’s plans, see [Update on Adobe Flash Player End of Support](<https://blogs.windows.com/msedgedev/2020/09/04/update-adobe-flash-end-support>). **12/8/20 REMINDER **Windows 10, version 1903 reached end of servicing on December 8, 2020. To continue receiving security and quality updates, Microsoft recommends that you update to the latest version of Windows 10. If you want to update to Windows 10, version 1909, you must use the Enablement Package KB4517245 (EKB). Using the EKB makes updating faster and easier and requires a single restart. For more information, see [Windows 10, version 1909 delivery options](<https://techcommunity.microsoft.com/t5/windows-it-pro-blog/windows-10-version-1909-delivery-options/ba-p/1002660>). **11/19/20** For information about Windows update terminology, see the article about the [types of Windows updates](<https://docs.microsoft.com/en-us/troubleshoot/windows-client/deployment/standard-terminology-software-updates>) and the [monthly quality update types](<https://techcommunity.microsoft.com/t5/windows-it-pro-blog/windows-10-update-servicing-cadence/ba-p/222376>). To view other notes and messages, see the Windows 10, version 1909 update history home page.**Note **Follow [@WindowsUpdate](<https://twitter.com/windowsupdate>) to find out when new content is published to the release information dashboard. **Note **This release also contains updates for Microsoft HoloLens (OS Build 18363.1108) released April 13, 2021. Microsoft will release an update directly to the Windows Update Client to improve Windows Update reliability on Microsoft HoloLens that have not updated to this most recent OS Build. ## Highlights * Updates to improve security when Windows performs basic operations. * Updates to improve security when using input devices such as a mouse, keyboard, or pen. ## Improvements and fixes This security update includes quality improvements. Key changes include: * Addresses an issue in which a principal in a trusted MIT realm fails to obtain a Kerberos service ticket from Active Directory domain controllers (DC). This occurs on devices that installed Windows Updates that contain CVE-2020-17049 protections and configured PerfromTicketSignature to 1 or higher. These updates were released between November 10, 2020 and December 8, 2020. Ticket acquisition also fails with the error, “KRB_GENERIC_ERROR”, if callers submit a PAC-less Ticket Granting Ticket (TGT) as an evidence ticket without providing the USER_NO_AUTH_DATA_REQUIRED flag. * Addresses an issue with security vulnerabilities identified by a security researcher. Because of these security vulnerabilities, this and all future Windows updates will no longer contain the [RemoteFX vGPU](<https://docs.microsoft.com/en-us/windows-server/virtualization/hyper-v/deploy/deploy-graphics-devices-using-remotefx-vgpu>) feature. For more information about the vulnerability and its removal, see [CVE-2020-1036](<https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2020-1036>) and [KB4570006](<https://support.microsoft.com/en-us/topic/update-to-disable-and-remove-the-remotefx-vgpu-component-in-windows-bbdf1531-7188-2bf4-0de6-641de79f09d2>). Secure vGPU alternatives are available using [Discrete Device Assignment (DDA)](<https://docs.microsoft.com/en-us/windows-server/virtualization/hyper-v/deploy/deploying-graphics-devices-using-dda>) in Windows Server LTSC releases (Windows Server 2016 and Windows Server 2019) and Windows Server SAC releases (Windows Server, version 1803 and later versions). * Addresses a potential elevation of privilege vulnerability in the way Azure Active Directory web sign-in allows arbitrary browsing from the third-party endpoints used for federated authentication. For more information, see [CVE-2021-27092](<https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-27092>) and [Policy CSP - Authentication](<https://docs.microsoft.com/en-us/windows/client-management/mdm/policy-csp-authentication#authentication-enablewebsignin>). * Addresses an issue that causes Windows Back up using File History to stop working for a few users. This issue occurs after installing the February 9, 2021 update. The error message is, “Failed to start the backup of user links (error 8007005)”. * Security updates to Windows App Platform and Frameworks, Windows Apps, Windows Input and Composition, Windows Office Media, Windows Fundamentals, Windows Cryptography, the Windows AI Platform, Windows Hybrid Cloud Networking, the Windows Kernel, Windows Virtualization, and Windows Media. 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, please refer to the new [Security Update Guide](<https://msrc.microsoft.com/update-guide>) website. **Windows Update Improvements**Microsoft has released an update directly to the Windows Update client to improve reliability. Any device running Windows 10 configured to receive updates automatically from Windows Update, including Enterprise and Pro editions, will be offered the latest Windows 10 feature update based on device compatibility and Windows Update for Business deferral policy. This doesn't apply to long-term servicing editions. ## Known issues in this update **Symptom**| **Workaround** ---|--- Scroll bar controls might appear blank on the screen and not function after installing this update. This issue affects 32-bit applications running on 64-bit Windows 10 (WOW64) that create scroll bars using a [superclass](<https://docs.microsoft.com/en-us/windows/win32/winmsg/about-window-procedures#window-procedure-superclassing>) of the **USER32.DLL SCROLLBAR** window class. This issue also affects **HScrollBar** and **VScrollBar** controls that are used in Visual Basic 6 applications and the classes derived from **[System.Windows.Forms.ScrollBar](<https://docs.microsoft.com/en-us/dotnet/api/system.windows.forms.scrollbar?view=net-5.0>)** that are used in .NET Windows Forms applications. A memory usage increase of up to 4 GB might occur in 64-bit applications when you create a scroll bar control.Scroll bars you create using the **SCROLLBAR** window class or using the WS_HSCROLL and WS_VSCROLL window styles function normally. Applications that use the scroll bar control that is implemented in **COMCTL32.DLL** version 6 are not affected. This includes .NET Windows Forms applications that call **Application.EnableVisualStyles()**.| This issue is resolved in KB5003169. ## How to get this update **Before installing this update**Prerequisite:You **must **install the April 13, 2021 servicing stack update (SSU) (KB5001406) or later before installing the latest cumulative update (LCU). SSUs improve the reliability of the update process to mitigate potential issues while installing the LCU and applying Microsoft security fixes. For general information about SSUs, see [Servicing stack updates](<https://docs.microsoft.com/en-us/windows/deployment/update/servicing-stack-updates>) and Servicing Stack Updates (SSU): Frequently Asked Questions.**Install this update****Release Channel**| **Available**| **Next Step** ---|---|--- Windows Update and Microsoft Update| Yes| None. This update will be downloaded and installed automatically from Windows Update. Microsoft Update Catalog| Yes| To get the standalone package for this update, go to the [Microsoft Update Catalog](<https://www.catalog.update.microsoft.com/Search.aspx?q=KB5001337>) website. Windows Server Update Services (WSUS)| Yes| This update will automatically sync with WSUS if you configure **Products and Classifications** as follows:**Product**: Windows 10, version 1903 and later**Classification**: Security Updates **File information**For a list of the files that are provided in this update, download the [file information for cumulative update 5001337](<https://download.microsoft.com/download/e/1/0/e10a6884-2e7a-4d80-ac2f-884c39a2a1b2/5001337.csv>).


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