Microsoft’s September 2026 Patch Tuesday landed Windows 11’s biggest visible interface refresh in months alongside what several vulnerability trackers are calling the largest single-month patch count on record. If you’ve seen KB5124008 or KB5124012 waiting in Windows Update and want to know what you’re actually installing, here’s the breakdown.
Which Update Applies to You
KB5124008 covers Windows 11 24H2 and 25H2 (builds 26100.9445 and 26200.9445). KB5124012 covers Windows 11 26H1. KB5122880 covers Windows 11 23H2, and Windows 10 gets a separate cumulative update, KB5122878. Check your version under Settings > System > About before assuming which changes below apply to you: the interface changes are specific to KB5124008, while 26H1 devices on KB5124012 get the same security fixes but a different, narrower set of non-security changes.
The Interface Changes (KB5124008 Only)
- Taskbar: can now be locked to the top, left, right, or bottom of the screen, plus a smaller, more compact taskbar size option. The search box and the compact taskbar are only supported in the top and bottom positions, so moving the taskbar to a side hides the search box.
- Start menu: a size toggle between small and large, an option to hide your signed-in name and picture, and a redesigned settings page with independent show/hide controls for the Pinned, Recommended, and All sections. The “Recommended” section itself has also been renamed “Recent.”
- Search: a simplified home view, clearer labeling of where each result actually comes from (your device, the web, or the Microsoft Store), a new privacy toggle that blocks web and Store suggestions from the search box entirely, and automatic indexing of frequently used folders.
The Security Side: Why This Was a Record Month
Vulnerability trackers put this release at somewhere between roughly 964 and 997 fixed vulnerabilities depending on counting method, the largest single-month Patch Tuesday total on record. Several outlets have linked the jump to Microsoft’s expanded use of AI-assisted vulnerability discovery across its own codebase. Two of the fixed flaws were already being exploited in the wild before the patch shipped: CVE-2026-81963, a link-following flaw in the Windows Update Stack that lets a local attacker reach SYSTEM privileges, and CVE-2026-85880, a heap-based buffer overflow in the Advanced Local Procedure Call (ALPC) component that lets code running inside a low-privilege AppContainer sandbox escape it with no user interaction required. More than 100 of the total fixes are rated critical, most of them remote-code-execution flaws affecting Remote Desktop Services, Windows DNS, Office, and SQL Server.
Smaller Fixes Worth Knowing About
- Resolves a bug that could cause Microsoft Teams and Outlook to close unexpectedly on Arm64-based PCs.
- Fixes a black-desktop bug tied to personalization settings.
- Corrects audio redirection issues in Remote Desktop sessions.
- Improves how Secure Boot certificates are delivered.
Known Issues and What Not to Do
The interface rollout is staged, so don’t assume something is broken if your taskbar or Start menu doesn’t look different immediately after installing; it can take time to reach every eligible device. Don’t uninstall or block this update just because you don’t like the new taskbar or Start layout, either. You can switch the taskbar back to the bottom and restore the previous size directly in Settings, but skipping the whole update also means going without fixes for two zero-days that are already being actively exploited elsewhere, which is a worse trade-off than a UI change you can reverse in a few clicks. If you hit a specific new problem after installing, such as a game crash or driver conflict, check whether it matches a widely reported pattern before assuming it’s this update specifically. Past cumulative updates, like August’s KB5121003, have caused separate, unrelated issues that were resolved in later cumulative updates rather than needing a rollback.
How to Install It
Go to Settings > Windows Update > Check for updates. It’s also available through Windows Update for Business, WSUS, and the Microsoft Update Catalog for managed and enterprise devices, and is rolling out now through all standard channels.
Related: Windows 11 July 2026 Update (KB5101650): What’s New and How to Install It · Windows 11 25H2, 26H1, and 26H2 Explained
FAQ
What’s the difference between KB5124008 and KB5124012?
KB5124008 applies to Windows 11 24H2 and 25H2 and includes the new taskbar, Start menu, and Search changes. KB5124012 applies to Windows 11 26H1 and carries the same security fixes but a different set of non-security changes, including Start menu reliability fixes and new touchpad gesture settings, without the taskbar and Search redesign.
Does this update fix any actively exploited vulnerabilities?
Yes. It patches two zero-days already exploited in the wild: CVE-2026-81963 in the Windows Update Stack and CVE-2026-85880 in the Advanced Local Procedure Call component, both of which let an attacker escalate privileges on an affected device.
Can I move the taskbar back to the bottom after installing this update?
Yes. The new taskbar position options are user-configurable in Settings, so you can lock it back to the bottom, the previous default, at any time. You don’t need to avoid or uninstall the update to keep the old layout.
Why did September 2026 have so many patched vulnerabilities?
Multiple vulnerability trackers put the total between roughly 964 and 997 fixes, the largest single-month total on record for Patch Tuesday. Analysts have linked the jump to Microsoft’s expanded use of AI-assisted vulnerability discovery across its own codebase, which is turning up issues faster than in previous years.