Microsoft Releases Windows 11 Security Update KB5124008, Fixes Mouse Cursor, Wallpaper, and App Crashes
Microsoft has rolled out the September 2026 monthly security update KB5124008 for Windows 11 24H2 and 25H2, bringing builds 26200.9278 and 26100.9278. The update resolves issues from an optional August update that caused custom mouse cursors to disappear and desktop wallpapers to turn black, affecting non-English systems. It also fixes crashes in Teams and Outlook on Arm devices, remote desktop audio redirection, and improves OMA-DM diagnostics.
In September 2026, Microsoft began pushing the monthly security update KB5124008 to users of Windows 11 24H2 and 25H2. After installation, the system version will be updated to Build 26200.9278 or 26100.9278. Users can obtain the update via the "Check for updates" feature in Windows Update.
The update addresses problems caused by an optional update released in late August. That optional update had caused some users to lose their custom mouse cursor styles and to see their desktop wallpaper turn black. Microsoft explained that the issue stemmed from a component modified by the update failing to load personalization settings, and that it affected only non-English systems. Because Microsoft engineers use English-language systems, the issue was not detected during internal testing. The optional update was not broadly distributed, so the impact was limited. In KB5124008, these issues have been fixed.
According to the update log, the problem where custom mouse cursor settings would not display correctly has been resolved, and the selected cursor options and colors now work as expected. The issue where desktop backgrounds and other personalization settings failed to load correctly, resulting in a black background, has also been fixed. On the security front, this update provides security improvements and addresses multiple known vulnerabilities; details are available in the MSRC-2609 log. Regarding Secure Boot, the update includes additional high-confidence device target data, so more devices will attempt to automatically update their UEFI Secure Boot certificates.
Additionally, this update fixes an issue where Teams and Outlook would close unexpectedly on Windows 11 on Arm devices, as well as a problem where remote desktop audio redirection would not play locally under certain configurations. The update also improves diagnostic logging for the Ooma-DM client to provide more information for troubleshooting device management server connection issues. The update has been distributed through the Windows Update channel and is also available from the Microsoft Update Catalog.