Should you update to KB5123273?
No: install KB5127648 instead. KB5123273 is a security update Microsoft released on 11 Aug 2026 for Windows PCs. It fixes 1 security flaw, 0 rated critical and 1 important by Microsoft.[1] None of them is known to be used in attacks.
It has since been replaced by KB5121003, released 11 Aug 2026, which includes all of its fixes. If you’re on an older version, install that instead.
Should you update?
No: install KB5127648 instead. KB5127648 came out on 13 Oct 2026 and includes every fix in KB5123273, so there’s no reason to stop at this one. Software Update offers the newest version your device can run.
Is KB5123273 still safe?
Not any more. The 4 updates since, up to KB5127648, fix 1,829 security flaws that KB5123273 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 1 security flaw, 0 rated critical and 1 important by Microsoft.[1] The critical or important one is:
| Flaw | Severity | What Microsoft calls it |
|---|---|---|
CVE-2026-6726 | Important | MITRE: CVE-2026-6726 TPM 2.0 Improper Object Slot Reuse |
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 26100.9168 or 26200.9168 or later.
Older devices
The same day, Microsoft released KB5121000 (183 security flaws), KB5120240 (160 security flaws) and KB5120249 (150 security flaws) for devices that stay on an older version. Each fixes the same holes where they apply.
KB5101650 vs KB5123273
KB5101650, released 14 Jul 2026, fixed 373 security flaws. KB5123273 fixes 1 security flaw and includes the fixes before it, so going straight to KB5123273 gets you both.
- Before: KB5101650, 14 Jul 2026, 373 security flaws
- After: KB5121003, 11 Aug 2026, 182 security flaws
- Windows updates, every release and the latest version
- Updates, the latest version of everything HARD tracks
References
- ^ Microsoft. “KB5123273”, 11 Aug 2026.