SNACK: 3-line summary
- Microsoft has confirmed that some Windows 11 devices with KB5127648 installed may be unable to re-enable Smart App Control.
- Devices where Smart App Control is already on are unaffected and remain protected.
- Microsoft offers registry and IT-managed Group Policy workarounds, while a permanent fix is still pending.
Microsoft currently lists a Smart App Control re-enabling problem affecting some devices after installation of KB5127648, the Windows 11 security update released on October 13, 2026. Devices where Smart App Control is already on are unaffected and remain protected.
Snackgirls react
AIKO: I’d like a diagnostic view that separates “protection running” from “ready to turn on.” Two states deserve two indicators.
Nea: If I found a mod tool or fan project from an unfamiliar source, I’d hesitate before opening it. I’d want to learn more about its creator first.
A greyed-out On option in Windows Security
KB5127648 applies to Windows 11 versions 24H2, 25H2 and 26H2. On some devices, the On option for Smart App Control may be greyed out. The feature blocks malicious, untrusted or potentially unwanted apps and works alongside Microsoft Defender or another antivirus.
To check the setting, open Windows Security > App & browser control > Smart App Control settings. Separately, look for KB5127648 under Settings > Windows Update > Update history. A greyed-out option alone does not establish that this update is the cause.
Two official workarounds, with precautions
Microsoft’s registry workaround involves an administrator Command Prompt, two registry override values and a restart. Before making changes, back up the registry and make sure you know how to restore it if something goes wrong. Follow the complete instructions in the official KB article.
For IT-managed devices, administrators can instead install and configure both special Group Policies listed in the KB article, set both to Enabled, then restart. One restores the ability to enable Smart App Control; the other provides troubleshooting logs. After either workaround, check the setting rather than assuming protection is on.
A permanent fix is still pending
Microsoft says it is working on a resolution for an upcoming release, with no firm fix date announced. The published steps are workarounds, not a permanent fix.
If Smart App Control is already on, leave it on; there is no need to switch it off to test for this issue. If you are uncomfortable editing the registry, ask for knowledgeable help and watch the official KB for updates. On a work PC, follow your IT department’s guidance.
Sources and checked date: October 19, 2026
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