Should you update to KB5129194?
No: install KB5127646 instead. KB5129194 is a security update Microsoft released on 14 Sep 2026 for Windows PCs. It fixes 2 security flaws, 1 rated critical and 1 important by Microsoft.[1] None of them is known to be used in attacks.
It has since been replaced by KB5127646, released 13 Oct 2026, which includes all of its fixes. If you’re on an older version, install that instead.
Should you update?
No: install KB5127646 instead. KB5127646 came out on 13 Oct 2026 and includes every fix in KB5129194, so there’s no reason to stop at this one. Software Update offers the newest version your device can run.
Is KB5129194 still safe?
Not any more. KB5127646 fixes 997 security flaws that KB5129194 doesn’t, and each became public the day its fix shipped. Installing it is safe: get it only from Start → Settings → Windows Update, never from a link in an email, text or pop-up.
What it fixes
Microsoft lists 2 security flaws, 1 rated critical and 1 important by Microsoft.[1] The 2 critical and important ones are:
| Flaw | Severity | What Microsoft calls it |
|---|---|---|
CVE-2026-85921 | Critical | Windows Secure Kernel Mode Elevation of Privilege Vulnerability |
CVE-2026-62721 | Important | Windows User-Mode Power Service (UMPS) Elevation of Privilege Vulnerability |
How to update, and how long it takes
Usually 15 to 60 minutes in all, with one or two restarts. You can keep working while it downloads.
- Save your work first.Windows restarts to finish the update, once or twice.
- Open Start → Settings → Windows Update.Select Check for updates. Windows downloads the month’s cumulative update; it includes every earlier fix.
- Restart when it asks.Select Restart now, or schedule it for tonight. Until it restarts, the fixes aren’t in place.
- Leave automatic updates on.In the same place, under Advanced options, turn on “Get me up to date” so restarts don’t wait for days.
To check it worked: Press Windows key + R, type winver and press Enter: it shows the OS build. It should say 28000.3231 or later.
Older devices
The same day, Microsoft released KB5129195 (1 security flaw) for devices that stay on an older version. Each fixes the same holes where they apply.
KB5124012 vs KB5129194
KB5124012, released 8 Sep 2026, fixed 637 security flaws, one already used in attacks. KB5129194 fixes 2 security flaws and includes the fixes before it, so going straight to KB5129194 gets you both.
- Before: KB5124012, 8 Sep 2026, 637 security flaws
- After: KB5127646, 13 Oct 2026, 997 security flaws
- Windows updates, every release and the latest version
- Updates, the latest version of everything HARD tracks
References
- ^ Microsoft. “KB5129194, out-of-band update”, 14 Sep 2026.