Windows 11 KB5120998 Broke Your Cursor and Wallpaper — Here’s Every Fix That Works

Executive summary: Windows 11 optional update KB5120998, released on 27 August 2026, is resetting mouse pointer personalization to a plain white default and flipping desktop wallpapers to solid black on builds 26100.9278 (24H2) and 26200.9278 (25H2). Microsoft has publicly acknowledged the cursor half of the problem but has not committed to a fix date. Because this was a preview release, its code is expected to land in the mandatory 8 September 2026 Patch Tuesday cumulative update — which means the window to deal with it on your own terms is closing.

What Actually Broke in KB5120998

KB5120998 shipped as an optional, non-security “preview” update on 27 August 2026. Within 24 hours, users on Reddit, the Feedback Hub and Microsoft’s own Q&A forums began reporting a consistent cluster of cosmetic-but-maddening regressions.

• Mouse pointer personalization is wiped. Custom cursor schemes, custom colors and high-DPI pointer sets revert to an oversized plain white arrow. Re-applying the setting appears to work, then reverts again after sign-out or restart.
• Wallpaper flips to solid black. The Personalization background switches itself to “Solid color” and, for a subset of users, keeps reverting to black after every reboot even after being manually changed back.
• Accessibility settings are ignored. Users who rely on enlarged or high-contrast pointers for visibility report that the Accessibility pointer controls have no effect while the bug is active — which makes this more than a cosmetic annoyance.
• Blurry or pixelated text. A smaller number of reports describe degraded font rendering that persists after re-running ClearType tuning.

One frequently-cited report on the DISM error 0x800f0915 is circulating alongside these complaints, but that error predates KB5120998 and does not appear to be caused by it.

Which Builds Are Affected

• Windows 11 version 25H2 — OS Build 26200.9278
• Windows 11 version 24H2 — OS Build 26100.9278

Microsoft’s release notes phrase the scope as updates “released August 27, 2026 (KB5120998) and later,” so newer builds in the same servicing branch may inherit the behaviour until a corrected package ships.

What Microsoft Has Said

On 29 August 2026, Microsoft quietly amended the KB5120998 release notes to state that it “has received reports indicating that mouse cursor personalization settings are being changed or reverted to certain standard settings,” and that it is investigating. Two things are worth noting about that wording:

• It acknowledges only the cursor issue. The black-wallpaper reset — which is arguably the more visible symptom — has not been separately confirmed, despite being reported alongside it consistently.
• It offers no timeline, no root cause and no committed fix. There is no out-of-band patch and no promise of one.

Fix It Now: A Step-by-Step Tutorial

Work through these in order. Steps 1 and 2 are non-destructive and resolve the problem for many users; step 3 is the guaranteed fix but costs you the update’s new features.

Step 1 — Confirm KB5120998 Is the Culprit

1. Press Windows + I to open Settings.
2. Go to Windows Update > Update history.
3. Look for KB5120998 under quality updates. If it is not listed, your cursor or wallpaper problem has a different cause and uninstalling nothing will help.
4. Optionally verify your build: press Windows + R, type winver and press Enter. You are looking for 26100.9278 or 26200.9278.

Step 2 — Re-apply Personalization Manually

To restore your wallpaper:

1. Open Settings > Personalization > Background.
2. Change Personalize your background from “Solid color” back to Picture, Slideshow or Windows Spotlight.
3. Re-select your image, then sign out and back in to confirm the setting survives a session change.

To restore your mouse pointer (Method A — Accessibility):

1. Open Settings > Accessibility > Mouse pointer and touch.
2. Re-select your pointer style, colour and size.
3. Restart or sign out and back in to test persistence.

To restore your mouse pointer (Method B — classic Mouse Properties):

1. Press Windows + R, type main.cpl and press Enter.
2. Open the Pointers tab.
3. Pick your scheme from the Scheme dropdown, or use Browse to re-point individual cursors at your .cur or .ani files.
4. Click Apply, then OK, and restart.

Method B writes directly to the legacy cursor scheme registry values and sticks more reliably than the Settings app for users with third-party cursor packs.

Step 3 — Uninstall KB5120998

1. Open Settings > Windows Update > Update history.
2. Scroll to Related settings and click Uninstall updates.
3. Find KB5120998 in the list and click Uninstall, confirming when prompted.
4. Restart your PC.
5. Re-apply your wallpaper and cursor settings using Step 2 — the uninstall does not automatically restore what was overwritten.

Important: KB5120998 is a non-security preview update, so removing it does not strip your machine of security patches. That is not true of the 8 September cumulative update — do not uninstall that one to chase this bug.

Step 4 — Stop It Coming Back

1. Go to Settings > Windows Update.
2. Turn off “Get the latest updates as soon as they’re available.” This toggle is the single biggest reason home users end up on preview builds without realising it.
3. If you need breathing room, use Pause updates for one to five weeks.
4. Never install optional preview updates on a production machine unless you specifically need a fix they contain.

The Catch: 8 September Patch Tuesday

Preview updates are Microsoft’s dry run. The code validated in an optional “C-week” release is normally folded into the following month’s mandatory security cumulative update. That places the KB5120998 payload in the 8 September 2026 Patch Tuesday rollout, which will install on virtually every consumer Windows 11 machine.

Two outcomes are possible. Either Microsoft ships a corrected build on 8 September and the problem quietly disappears for everyone, or the regression rides along into the mandatory update and the affected population multiplies overnight. Nothing Microsoft has published so far tells us which. If you have already uninstalled KB5120998, take a moment before 8 September to export your cursor scheme and note your wallpaper path, so restoring takes 60 seconds rather than an evening.

What KB5120998 Gets Right

The update is worth having once it is stable, which is why “uninstall and forget” is not the ideal end state. It brings a genuinely useful batch of interface changes:

• Taskbar on any screen edge, finally returning a layout option Windows 11 removed at launch, plus a smaller taskbar size for cramped displays.
• Start menu sizing with Small, Large and Automatic options, and a toggle to hide your profile name and picture — a small but real privacy win for anyone who screen-shares.
• Cleaner Windows Search that labels each result by type (app, file, web, Store) and lets you switch off Bing and Microsoft Store suggestions.
• Administrator Protection begins rolling out, using just-in-time elevated privileges instead of a standing admin token. It is disabled by default for now.
• Faster File Explorer, with a noticeably quicker Home page launch.
• WMIC removal. The deprecated command-line utility is gone; WMI itself is unaffected, but any script still calling wmic will break. Audit your automation now.

Key Takeaways

• Check before you panic. If KB5120998 is not in your update history, this is not your bug.
• Try Mouse Properties (main.cpl) before uninstalling. It is the fastest non-destructive fix and works for a meaningful share of affected users.
• Uninstalling is safe here because KB5120998 carries no security payload — a rare situation you should not generalise to other updates.
• Turn off “get the latest updates as soon as they’re available.” Most people hit by this never intended to run preview code.
• Watch 8 September. Whether this becomes a footnote or a mass-scale headache is decided by that Patch Tuesday build.
• Back up your personalization. Note your wallpaper file path and cursor scheme name now; it makes every future recovery trivial.

This article reflects publicly reported information as of 4 September 2026. Microsoft’s investigation is ongoing and the guidance above may change once an official fix ships.