Microsoft fixes Smart App Control broken by October Windows update

Microsoft has resolved a known issue that prevented some users from activating the Smart App Control security feature after installing the October 2026 KB5127648 Windows 11 security update.

Smart App Control uses Microsoft's code integrity features and app intelligence services, and it works alongside SmartScreen and Microsoft Defender to block potentially harmful apps or binaries.

As the company explained when it acknowledged the issue last month, the Smart App Control option is grayed out and cannot be toggled on affected devices running Windows 11 24H2 and later.

"After installing this update, some devices might be unable to turn on Smart App Control in the Windows Security app if it has been turned off. On affected devices, the option to turn on Smart App Control might be grayed out," Microsoft said in the KB5127648 advisory. "Devices where Smart App Control is already turned on are not affected and remain protected."