KB5127648 — Microsoft’s October 2026 Windows 11 security update, breaks Smart App Control on some devices running Windows 11 version 24H2 or later. The feature, which blocks untrusted apps using Microsoft’s app intelligence and code integrity checks, becomes grayed out and non-toggable if it was previously turned off. Devices where Smart App Control was already enabled remain unaffected and stay protected. No fix is available yet. Microsoft has published registry and Group Policy workarounds for IT administrators only. The issue does not affect end users who never disabled the feature. It also does not impact Windows 11 versions earlier than 24H2. The problem appears alongside two other confirmed post-update bugs: Remote Desktop failures for non-admin users when ‘Administrator protection’ is on, and lingering Always On VPN issues tied to September’s updates. A separate black-screen and Explorer crash bug. First seen after August’s rollouts, has now been resolved. Microsoft says the KB5127648 advisory has been updated with the Smart App Control note. Registry instructions require command-line execution and a reboot. Group Policy fixes demand configuration under Computer Configuration > Administrative Templates > {Group Policy name} > Windows 11, version 24H2, 25H2. Then setting both policies to Enabled and restarting. The workaround applies only to enterprise-managed devices. There is no public-facing toggle, patch or consumer fix announced. Windows 11 users searching for 'windows 11' and encountering this issue will find no in-app recovery path, only administrative intervention. Microsoft has not stated when a permanent fix will ship.