December 8, 2020—KB4592438 (OS Builds 19041.685 and 19042.685)

**NEW 12/8/20
IMPORTANT **Adobe Flash Player will go out of support on December 31, 2020. For more information, see Adobe Flash end of support on December 31, 2020. Flash content will be blocked from running in Flash Player beginning January 12, 2021. For more information, see Adobe Flash Player EOL General Information Page.

11/17/20
For information about Windows update terminology, see the article about the types of Windows updates and the monthly quality update types. To view other notes and messages, see the Windows 10, version 2004 update history home page.NoteFollow @WindowsUpdate to find out when new content is published to the release information dashboard.

11/10/20
IMPORTANT Because of minimal operations during the holidays and the upcoming Western new year, there won’t be a preview release (known as a “C” release) for the month of December 2020. Normal monthly servicing for both B and C releases will resume in January 2021.

Highlights

• Updates to improve security when using Microsoft Edge Legacy.
• Updates to improve security when using Microsoft Office products.

Improvements and fixes

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Windows 10, version 20H2

This security update includes quality improvements. Key changes include:

• This build includes all the improvements from Windows 10, version 2004.
• No additional issues were documented for this release.

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Windows 10, version 2004

NoteThis release also contains updates for Microsoft HoloLens (OS Build 19041.1131) released December 8, 2020. 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.

This security update includes quality improvements. Key changes include:

• Addresses an issue that might cause system and user certificates to be lost when updating a device from Windows 10, versions 1809 or later to a later version of Windows 10.
• Security updates to Microsoft Edge Legacy, the Microsoft Graphics Component, Windows Media, Windows Fundamentals, and Windows Virtualization.
  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 website.

Windows Update ImprovementsMicrosoft 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
When using the Microsoft Japanese Input Method Editor (IME) to enter Kanji characters in an app that automatically allows the input of Furigana characters, you might not get the correct Furigana characters. You might need to enter the Furigana characters manually.Note The affected apps are using theImmGetCompositionString() function.	This issue is resolved in KB5005101.
A small number of devices that have installed this update have reported that when running chkdsk /f, their file system might get damaged and the device might not boot.** **	This issue is resolved and should now be prevented automatically on non-managed devices. Please note that it can take up to 24 hours for the resolution to propagate to non-managed devices. Restarting your device might help the resolution apply to your device faster. For enterprise-managed devices that have installed this update and encountered this issue, it can be resolved by installing and configuring a special Group Policy. To find out more about using Group Policies, see Group Policy Overview.To mitigate this issue on devices which have already encountered this issue and are unable to start up, use the following steps:

1. The device should automatically start up into the Recovery Console after failing to start up a few times.
2. Select Advanced options.
3. Select Command Prompt from the list of actions.
4. Once Command Prompt opens, type:chkdsk /f 5. Allowchkdskto complete the scan, this can take a little while. Once it has completed, type:exit 6. The device should now start up as expected. If it restarts intoRecovery Console, selectExit and continue to Windows 10.NoteAfter completing these steps, the device might automatically runchkdsk again on restart. It should start up as expected once it has completed.

How to get this update

Before installing this updateMicrosoft strongly recommends you install the latest servicing stack update (SSU) for your operating system 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 and Servicing Stack Updates (SSU): Frequently Asked Questions.If you are using Windows Update, the latest SSU (KB4593175) will be offered to you automatically. To get the standalone package for the latest SSU, search for it in the Microsoft Update Catalog.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 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 laterClassification: Security Updates File informationFor a list of the files that are provided in this update, download the file information for cumulative update 4592438.Note Some files erroneously have “Not applicable” in the “File version” column of the CSV file. This might lead to false positives or false negatives when using some third-party scan detection tools to validate the build.