KB5025221

Devices with Windows installations created from custom offline media or custom ISO image might have Microsoft Edge Legacy removed by this update, but not automatically replaced by the new Microsoft Edge. This issue is only encountered when custom offline media or ISO images are created by slipstreaming this update into the image without having first installed the standalone servicing stack update (SSU) released March 29, 2021 or later.

Note Devices that connect directly to Windows Update to receive updates are not affected. This includes devices using Windows Update for Business. Any device connecting to Windows Update should always receive the latest versions of the SSU and latest cumulative update (LCU) without any extra steps. 

To avoid this issue, be sure to first slipstream the SSU released March 29, 2021 or later into the custom offline media or ISO image before slipstreaming the LCU. To do this with the combined SSU and LCU packages now used for Windows 10, version 20H2 and Windows 10, version 2004, you will need to extract the SSU from the combined package. Use the following steps to extract the SSU:

1. Extract the cab from the msu via this command line (using the package for KB5000842 as an example): expand Windows10.0-KB5000842-x64.msu /f:Windows10.0-KB5000842-x64.cab <destination path>

2. Extract the SSU from the previously extracted cab via this command line: expand Windows10.0-KB5000842-x64.cab /f:* <destination path>

3. You will then have the SSU cab, in this example named SSU-19041.903-x64.cab. Slipstream this file into your offline image first, then the LCU.

If you have already encountered this issue by installing the OS using affected custom media, you can mitigate it by directly installing the new Microsoft Edge. If you need to broadly deploy the new Microsoft Edge for business, see Download and deploy Microsoft Edge for business.

You might have intermittent issues saving, copying, or attaching files using 32-bit apps, which are large address aware and using the CopyFile API. Windows devices are more likely to be affected by this issue when using some commercial or enterprise security software that uses extended file attributes. Microsoft Office apps, such as Microsoft Word or Microsoft Excel are only affected when using 32-bit versions and you might receive the error, "Document not saved."

This issue is unlikely to be experienced by consumers using Windows devices in their home or on non-managed commercial devices. Apps are not affected by this issue if they are 64-bit or 32-bit and NOT large address aware.

This issue is resolved in KB5027215.