Microsoft said that its October 2026 security update for Windows 11 (KB5127648, released October 13) may cause a problem with Smart App Control. This is a Windows feature that blocks untrusted apps. Microsoft said some devices might be unable to turn it on in the Windows Security app if it was switched off. On those devices, the option may be grayed out. The update covers Windows 11 versions 24H2, 25H2 and 26H2. Microsoft also said devices that already have the feature on are not affected and stay protected.
Microsoft did not say how many devices are affected or what causes the fault. It did not give a date for a fix. It said it is working on a resolution and will share an update in an upcoming release. For now, Microsoft listed two workarounds. Users can add two registry values and restart. IT administrators of managed devices can install and enable two special Group Policies. Microsoft said both policies are needed. The first turns the feature on, and the second keeps logging available for troubleshooting.
Teams that manage Windows 11 fleets should check whether any devices have Smart App Control switched off before they roll out this update. Those devices may not be able to turn it back on until the workaround is applied or Microsoft ships a fix. The same update is also the last one for Windows 11 24H2 Home and Pro, according to Microsoft.