Windows 11 Update KB5127648 Can Stop You Turning On Smart App Control: The Workaround
Machines that already have the feature on are unaffected, and Microsoft has given no date for a permanent fix.
Microsoft has confirmed a bug in its October Windows 11 security update that stops some users from switching on Smart App Control. The update, KB5127648, was released on October 13, and the problem was reported on October 16 by Windows Report and BleepingComputer, with gHacks following on October 17.
What the update broke
Smart App Control is the Windows 11 feature that blocks untrusted or unsigned applications. After installing KB5127648, some devices where the feature was turned off show its toggle in Windows Security greyed out, so it cannot be enabled. Microsoft says PCs where Smart App Control was already on are not affected and "remain protected." It has not said how many devices are affected.
| KB5127648 (October 13, 2026) | Build |
|---|---|
| Windows 11 24H2 | 26100.9711 |
| Windows 11 25H2 | 26200.9711 |
| Windows 11 26H2 | 26300.9711 |
Build numbers are from Microsoft's KB5127648 support page. To check whether you have it, open Settings, Windows Update, Update history.
The workarounds
Microsoft says it is working on a resolution for an upcoming release, and you do not need to uninstall the update.
For individual users (administrator rights and a restart needed):
1. Back up the registry or create a restore point first; a wrong registry edit can cause problems.
2. Open Command Prompt as administrator and run the two commands Microsoft lists in the KB advisory. They add two DWORD values, 2883193997 and 2850574478, set to 1, under HKLM\SYSTEM\CurrentControlSet\Policies\Microsoft\FeatureManagement\Overrides.
3. Restart, then open Windows Security, App & browser control, Smart App Control settings, and turn it on.
Copy the exact commands from Microsoft's page rather than a blog. On work or school PCs, organisation policies may override the change, so ask your IT team. Most home users may prefer to wait for Microsoft's fix.
For IT administrators: install the two Group Policy packages "KB5074105 261015_19222 Feature Preview" and "KB5074105 261015_19221 Feature Preview", set both to Enabled and restart. The first re-enables Smart App Control; the second turns on troubleshooting logging (BetaNews).
What Microsoft has not said
There is no date for a permanent fix, and Microsoft has not said whether it will come as a separate update or in a monthly release. Nothing in the reporting suggests the bug exposes devices to new risk by itself; it only prevents the feature being enabled. An unverified reader comment on gHacks claims that turning Smart App Control off now shows a warning that it cannot be re-enabled without a PC reset; that has not been confirmed.
Advice for now
If Smart App Control is on, leave it on. Do not skip KB5127648 over this bug, since its security fixes still matter. Businesses should test on a pilot group before wide deployment.
What to watch next
A formal entry on Microsoft's Release Health page, a fix timeline, and the next monthly security release.
