Windows 11 KB5120998 Can Reset Desktop Backgrounds to Black — What IT Admins Need to Know

A Windows preview update released on 27 August 2026 is causing desktop backgrounds to show as solid black on some Windows 11 24H2 and 25H2 devices. Microsoft confirmed the issue on 2 September 2026. The symptom looks identical to a user manually setting a solid black background — but that is not what happened. The issue is deeper than the wallpaper setting itself: some Windows Desktop settings fail to load correctly on affected devices (Microsoft does not name a specific service), and trying to fix it from inside Settings does not work because the same load failure repeats the moment you try.

Microsoft fixed this in KB5124008 (8 September 2026). The correct action is simply to install that update or any later cumulative update. Identifying which devices took KB5120998 is still useful for confirming your exposure, but uninstalling the preview is no longer the recommended remedy.

The problem: what KB5120998 is actually doing

KB5120998 is the August 27, 2026 Windows 11 preview update for the 24H2 release (OS Build 26100.9278). Preview updates — sometimes called “optional” or “non-security preview” updates — ship at the end of each calendar month and contain the fixes slated for the following month's mandatory security release. Organisations that want early access to fixes often deploy them to validate compatibility before the full rollout. This time, one of those fixes introduced a regression.

On affected devices, after installing KB5120998, Windows Desktop settings stop loading correctly. The result is that the background reverts to a solid black colour. Microsoft's own confirmed description is direct: “some Windows Desktop settings fail to load, resulting in desktop backgrounds displaying as a solid black color.” The same problem can also affect slideshow backgrounds and contrast themes — any desktop setting that goes through the same settings-loading path.

It is important to know what kind of update this is. KB5120998 is a preview update, not the mandatory August 2026 security update. The monthly security update (released on Patch Tuesday, the second Tuesday of each month) is a separate KB number and is not known to have this problem. Devices that only install security updates and have not opted in to preview updates are not affected.

Why it happens: a settings load failure, not a wallpaper preference

The reason this problem cannot be fixed from inside Settings is subtle, and it matters for understanding why “just go change the wallpaper” is not a solution.

Windows Desktop settings — the wallpaper, the slideshow, the accent colour, the contrast theme — are not stored in a single file that Windows reads and applies at login. They are loaded on demand through a settings subsystem. When that subsystem encounters an error, it does not silently use whatever value was last written; it falls back to a hard-coded default, which for the background is solid black.

When a user opens Settings and selects a new wallpaper, Windows writes the new value and then immediately tries to load it through the same subsystem that is already broken. The write succeeds — the preference is saved — but the load fails, and the black default is used again. From the user's perspective, their change simply did not take. From Windows' perspective, the new value is sitting there correctly, but the code path that would actually apply it is where the regression lives.

Microsoft's confirmed statement is direct: “On affected devices, attempting to manually restore customized settings does not work. This is because the issue prevents the correct loading of settings, regardless of their value.”

The same update is also causing mouse cursor customisations to reset on non-English Windows installations — a separate symptom from the same root cause pattern. If devices are showing both a black background and cursor resets, KB5120998 is the single source of both.

How to verify: find affected devices before users call the helpdesk

The first thing to establish is which devices in the fleet actually have KB5120998 installed. Not every Windows 11 device will have it — only those that either manually checked for updates in the last week of August, or those where a policy explicitly pushes preview updates.

Run this in PowerShell to check a single device:

Get-HotFix -Id KB5120998

Source        Description      HotFixID   InstalledBy          InstalledOn
------        -----------      --------   -----------          -----------
DESKTOP-ABC   Update           KB5120998  NT AUTHORITY\SYSTEM  27/08/2026 00:00:00

If the command returns output like the above, the update is installed. If the update is absent, Get-HotFix -Id throws a terminating “Cannot find the requested hotfix” error rather than returning silently — wrap it in try/catch or use -ErrorAction SilentlyContinue when scripting. Note too that Get-HotFix reads Win32_QuickFixEngineering, which only reports CBS-supplied updates, so a negative result is not conclusive proof of absence.

At fleet scale, use the OS build number to identify affected devices. Devices on OS Build 26100.9278 received KB5120998. In Intune, navigate to Devices › All devices and filter by OS version, or run a device query. Any device reporting build 26100.9278 is in scope.

The fix: uninstall KB5120998 or wait for the patch

This is resolved. Microsoft’s release-health entry “Desktop background settings are lost or reset on some devices” is marked Resolved, KB5124008 as of 8 September 2026. Install KB5124008 or later and the personalization settings load normally again. The options below remain only for devices that genuinely cannot take the September security update yet:

Option 1 — Do nothing and wait (low-risk environments)

If KB5120998 was not deployed to your fleet intentionally, and the number of affected devices is small, the simplest path is to wait for Microsoft's fix. The issue is cosmetic from a productivity standpoint — users can still work normally, all applications run correctly, and the September 2026 security update (when it ships) should include the fix.

Option 2 — Uninstall KB5120998

If the number of affected devices is large, or if user complaints warrant action, uninstalling KB5120998 removes the root cause immediately. On the next login after the uninstall and restart, desktop background settings load normally again.

To uninstall on a single device:

# NOTE: wusa.exe /uninstall cannot remove a combined SSU+LCU cumulative
# update - that has been unsupported since 2021. It fails rather than
# uninstalling. Use DISM against the LCU package identity instead:

Get-WindowsPackage -Online | Where-Object { $_.PackageName -like '*5120998*' }

DISM /online /Remove-Package /PackageName:<LCU package identity from above>

# The servicing stack update (SSU) component cannot be removed at all.
# Restart separately when ready
Restart-Computer

The wusa.exe command runs silently and completes on restart. Do not pass /forcerestart without warning the user — it shuts Windows down immediately with no save prompt.

To uninstall via Settings, navigate to Settings › Windows Update › Update history › Uninstall updates. Find “2026-08 Preview of Cumulative Update for Windows 11 Version 24H2 (KB5120998)” in the list and select Uninstall. A restart is required.

At fleet scale through Intune: Intune does not support a direct “uninstall this specific update” policy. For fleet-scale removal, the options are:

1. Script deployment via Intune — deploy a DISM-based removal script targeting affected devices (wusa.exe /uninstall does not work on cumulative updates), with a separate restart scheduled via Intune's restart notification policies.
2. Windows Update ring configuration — if the preview update was pushed through a Windows Update ring, pause that ring immediately so no additional devices receive it. Already-affected devices still need the uninstall command.
3. Configuration Manager — if you manage updates through ConfigMgr, decline KB5120998 in the Software Update Point to prevent further deployments, and create a deployment to uninstall it on already-affected devices using a script package.

Option 3 — Block future deployment of preview updates

If this is the first time preview updates reached production devices unintentionally, configure the right Windows Update policies now. These prevent optional preview updates from being offered to managed devices.

CSP / OMA-URI:

• Path: ./Device/Vendor/MSFT/Policy/Config/Update/AllowOptionalContent
• Data type: Integer
• Value: 0 (blocks optional/preview updates)

Group Policy path: Computer Configuration › Administrative Templates › Windows Components › Windows Update › Manage updates offered from Windows Server Update Services › Allow Optional Updates — set to Disabled.

Proof it worked

After uninstalling KB5120998 and restarting, confirm the update is no longer present:

Get-HotFix -Id KB5120998

# If nothing is returned, the update is no longer installed.
# Also check the OS build has dropped back from 26100.9278:

(Get-ItemProperty "HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion").CurrentBuildNumber
(Get-ItemProperty "HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion").UBR

A “Cannot find the requested hotfix” error from Get-HotFix indicates the update is gone (it throws rather than returning an empty result). The UBR (Update Build Revision) value should be lower than 9278 on the same build 26100.

On the device, open Settings › Personalization › Background. The setting should now load normally and changes should apply immediately without reverting to black. If the user had a custom wallpaper set before the issue started, they will need to re-apply it — the setting was saved but not loading; after the fix it should appear, but if it still shows black they simply need to pick their wallpaper again from Settings.

References

• Windows 11, version 24H2 known issues and notifications — Microsoft's release health dashboard. The desktop background entry is in the September 2026 section, status: Confirmed. This is the authoritative source for current issue status and when the fix ships.
• KB5120998 — 2026-08 Preview of Cumulative Update for Windows 11 Version 24H2 — the Windows Update catalog entry for the affected update, with full changelog, installation details, and the link to uninstall instructions.
• Policy CSP — Update/AllowOptionalContent — the Intune CSP reference for blocking optional and preview Windows updates from being offered to managed devices.