Windows’ August optional update brought the Start menu makeover everyone asked for - plus confirmed bugs that replaced custom cursors with a giant white pointer and turned wallpapers black. Microsoft has since fixed both, and the fix arrived in the September 8 update. Uninstalling is no longer the end of the story: what you install this month matters more than what you skipped last month. Skip the August update - and install September’s, because it also patches two holes being exploited right now. There is also an October 13 deadline for 24H2 users that does not care about your patience.
Every month, Windows gets a security update on the second Tuesday. That is Patch Tuesday, and it is the update you should always install. The August 27 optional update is a different animal: it is a preview of the features coming in September, and it has become this month’s cautionary tale. Here is what happened, what to do about it, and the date you cannot skip.
What is KB5120998?
KB5120998 is the optional Windows 11 update Microsoft released on August 27, 2026. It is offered to every PC running Windows 11 24H2 or 25H2 - builds 26200.9278 on 25H2 and 26100.9278 on 24H2 - and you do not have to join any test program to see it.
It does not install itself. Optional updates sit in Windows Update with an Install button and wait for you to click. But this one is the year’s headline release: it ships a resizable Start menu, a movable taskbar, and a decluttered Search box without Bing. That is why so many people clicked it.
What is the cursor bug?
The update resets your cursor to a large, white, default pointer - the kind that looks like Windows 98 - and then refuses to save any change you make. Pick a smaller cursor or a different color, and it snaps back to the broken default. Some users report the cursor disappearing entirely or flipping color, like a white cursor turning large and black.
This is not a rumor. Microsoft updated its release notes to acknowledge it: “Microsoft has received reports indicating that mouse cursor personalization settings are being changed or reverted to certain standard settings. This occurs following installation of Windows updates released August 27, 2026 (KB5120998) and later.”
The company said it was investigating, and at the time there was no official fix. Everyone who tried uninstalling the update got their cursor back. That changed on September 8: KB5124008 fixes it, and uninstalling is no longer necessary.
What about the wallpaper?
A second major complaint: the update wipes your desktop background and replaces it with solid black. Set your wallpaper again, and it comes back black after the next restart or logout. Some people hit both bugs at once - black wallpaper and an oversized cursor on the same machine.
There is also a third, less common report of blurry fonts on some systems. Microsoft acknowledged the wallpaper issue on September 2 - noting that the wallpaper could not be restored manually in the meantime - and the September 8 update fixed it along with the cursor. Uninstalling KB5120998 resolved all three for everyone who tried it at the time.
Is it fixed now? Yes - and installing it matters this month
KB5124008, the September 8 Patch Tuesday update, fixes both the cursor bug and the wallpaper bug. After you install it, your build number reads 26100.9445 on 24H2 or 26200.9445 on 25H2. If you skipped the August preview, you get the new Start menu, taskbar, and Search features with it anyway - without the bugs.
This month, though, the reason to install it is bigger than cosmetics. KB5124008 also patches two vulnerabilities that are being actively exploited:
- CVE-2026-85880 - a heap overflow in a core Windows component that can be used to escape the browser sandbox. Microsoft describes it as affecting the Windows fleet broadly, not one product.
- CVE-2026-81963 - a flaw in the Windows Update Stack itself. It is the first Windows Update Stack vulnerability exploited in the wild since 2022.
There is no workaround for either one. Installing the update is the only fix, and it is the rare month where waiting two weeks costs you something real. That is the exception to the routine I laid out in the five-step update routine: waiting protects you from buggy updates, but it does not protect you from holes that are already being used.
Did it break every PC?
No. Plenty of people installed it with no trouble at all - Windows Latest’s own test machine was fine. The bug turned out to be scoped to non-English code components, which Microsoft pinned down on September 1, and it was fixed on September 8 in KB5124008.
That is exactly the situation where you wait. You do not know whether your PC is affected, and the cost of waiting is one week. The cost of not waiting is an oversized cursor you cannot fix without a full uninstall.
Should I have installed it?
Not at the time. Three reasons, and note that none of them apply to September’s update:
- It was optional. Skipping it cost you nothing - you were not missing security fixes, because the security fixes were in the August 11 Patch Tuesday update, which is separate and should already be installed.
- The only fix for the bugs was uninstalling, which also removed the features you wanted.
- Everything this update shipped arrived again on September 8 in KB5124008 - this time without the cursor and wallpaper bugs, and with the fixes for them included.
This is the same two-week rule from the safe update routine: when an update lands, you do not have to be the first person to install it. Waiting lets other people find the problems so you do not have to.
I already installed it. How do I uninstall it?
If your cursor or wallpaper broke, uninstall the update:
- Open Settings
- Go to Windows Update
- Click Update history
- Click Uninstall updates
- Select KB5120998
- Click Uninstall, then restart
At the time, that was the only fix that worked. People tried resetting the registry, running DISM, and switching cursor schemes - none of it stuck. Uninstalling was the one move that fixed the cursor and wallpaper for everyone who tried it. If you are still hitting the bug today, you do not need to uninstall: install KB5124008, which is the official fix and keeps the features.
Yes, uninstalling removes the new Start menu, taskbar, and Search features too. That was the right trade at the time. The features came back with the September 8 update, KB5124008, which carries the cursor and wallpaper fixes as well - so the clean path now is to install that, not to stay on the older build. Microsoft may also have pulled the bad update back from your PC in the meantime through a Known Issue Rollback, its behind-the-scenes way of undoing an update without you doing anything.
This is not the first time this year that uninstalling was the answer. The July update broke Dell PCs so badly that Microsoft shipped an emergency out-of-band fix - I wrote up what to do when an update breaks your computer. The rollback step is the same every time.
What if I installed it and everything looks fine?
You can keep it and enjoy the new features. Or you can uninstall it, though that is no longer necessary - the September update supersedes it either way. Both are defensible. What matters now is installing KB5124008, which fixes the bugs if you have them and patches the two exploited holes whether you do or not.
The deadline you cannot skip: October 13
Here is the part of this story that is not going away in September. Windows 11 24H2 - the version most home PCs are running - reaches end of updates on October 13, 2026, for Home and Pro editions. After that date, 24H2 stops receiving monthly security updates, fixes for known issues, and time zone updates. The version does not stop working. It just stops being protected, and the gap grows every month.
That date comes from Microsoft’s own lifecycle page, and it changes the math of “wait two weeks before every update.” Waiting works when the version you run still gets updates. Waiting forever does not work when your version has a stop date. You need to be on 25H2 (or newer) before October 13.
Check which version you are on: press Win + R, type winver, and press Enter. If the window says 24H2, you have a deadline. If it says 25H2 or later, you are already on the supported path.
Here is the good news: for most home PCs, 25H2 installs itself. Microsoft pushes it automatically to unmanaged machines, and it arrives as an enablement package - a small switch that turns on features already sitting on your disk, not a full reinstall. If you have been pausing updates or deferring the feature update, this is the reason to let it through: the automatic upgrade is the thing that keeps you supported past October 13.
I wrote the full prep checklist for the 25H2 arrival - Windows 11 25H2 Is Installing Itself - What to Check Before It Lands. The three checks: back up your files, read the known-issues page, update your drivers. It takes about half an hour, and it is the difference between arriving at the deadline prepared and arriving at it surprised.
What to do now
- Install KB5124008, this month’s Patch Tuesday update. This is the month the two-week wait does not apply: two of the holes it patches are already being exploited, and there is no workaround for either.
- If your cursor or wallpaper is still broken, KB5124008 fixes both. You no longer need to uninstall anything.
- If KB5120998 is still sitting uninstalled in your update list, leave it. It is superseded, and there is no reason to install it now.
- Check your version with winver. If you are on 24H2, read the 25H2 prep checklist and let the feature update through before October 13.
- Once you are patched, the safe update routine applies again - wait a few days after Patch Tuesday, then check the release health page before you install. It is the same routine I laid out in Windows’ August Update Is Out - The Five-Step Routine.
The August optional update was a skip. September’s is not. Install KB5124008, check your version, and let 25H2 through on your schedule - before the October 13 deadline picks the schedule for you.
Sources
- Microsoft KB5124008 - the September 8 update that fixed both bugs
- Microsoft Security Update Guide - the two zero-days patched in the same update
- Microsoft KB5120998 - the August 27 optional update
- Microsoft Windows release health - official known-issues page, including the cursor acknowledgment
- Windows 11 Home and Pro lifecycle - 24H2 end of updates October 13, 2026
- Windows Latest - skip this update - first reporting on the cursor and wallpaper bugs
- Windows Latest - Microsoft’s acknowledgment
- 9to5Windows - what to do about KB5120998
Want more practical tech guides like this one? They land in your inbox every week. Sign up for the newsletter - no spam, unsubscribe anytime.