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Yes—Microsoft has confirmed a Smart App Control (SAC) problem in Windows 11 update KB5127648. Released October 13, 2026, for Windows 11 versions 24H2, 25H2 and 26H2, the update can leave SAC unable to be re-enabled after it was previously turned off. In Windows Security, the switch may appear unavailable or grayed out. PCs that already had SAC enabled remain protected against this specific bug.
What KB5127648 changes
Microsoft’s KB5127648 release notes state that “some devices might be unable to turn on Smart App Control in the Windows Security app if it has been turned off.” The issue concerns the ability to restore SAC, not the protection status of systems where SAC was already enforcing.
The update applies to Windows 11 24H2, 25H2 and 26H2. Microsoft has not published an independent affected-device count or prevalence rate, so the scope among eligible PCs is unknown.
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- Open Settings.
- Select Windows Security.
- Open App & browser control.
- Select Smart App Control settings.
- Check whether SAC is Off and whether its control is grayed out or refuses to switch on.
Also check Settings > Windows Update > Update history for KB5127648. A grayed-out control has other possible causes, including policy management or SAC’s normal compatibility decisions, so the update history and the fact that SAC was previously disabled are important clues.
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Why Smart App Control matters
Microsoft Learn describes SAC as an app-execution control that combines Microsoft’s app-intelligence services with Windows code integrity. In enforcement mode, Windows allows applications recognized as safe or signed with a certificate trusted through Microsoft’s Trusted Root Program, and blocks software that does not meet those checks.
SAC is not suitable for every workflow. Some legitimate developer, corporate and specialized-software scenarios do not fit its enforcement model, and Microsoft says SAC can automatically turn itself off for those users. The October regression affects the newer ability to turn SAC back on without reinstalling Windows.
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Why this workflow existed
In April 2026, Microsoft announced that Windows 11 25H2 could let users toggle SAC from Windows Security without a reinstall. KB5127648’s regression interferes with that newer workflow. This explains why a device can be healthy in every other respect yet show an unavailable SAC switch after the update.
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Home-user workaround: registry overrides
Microsoft documents two FeatureManagement overrides. They are a temporary mitigation, not a replacement for the promised product fix. Back up the registry before changing it: open regedit, select Computer, choose File > Export, save an .reg backup, and then close Registry Editor.
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- Open Command Prompt as administrator. Search for
Command Prompt, right-click it, and choose Run as administrator. - Run the first Microsoft-documented command exactly as shown:
reg add "HKLMSYSTEMCurrentControlSetPoliciesMicrosoftFeatureManagementOverrides" /v 2883193997 /t REG_DWORD /d 1 /f - Run the second command:
reg add "HKLMSYSTEMCurrentControlSetPoliciesMicrosoftFeatureManagementOverrides" /v 2850574478 /t REG_DWORD /d 1 /f - Restart Windows.
- Return to Settings > Windows Security > App & browser control > Smart App Control settings and check whether the control can be enabled.
Do not improvise value names, change unrelated registry entries, or skip the restart. If the switch remains unavailable, restore the exported registry backup only if needed and investigate policy or compatibility causes rather than repeatedly editing the values.
Enterprise workaround: special Group Policies
For managed devices, Microsoft lists two special Group Policies in the KB5127648 article. Administrators should deploy and configure both policies: one restores the SAC toggle and the other enables logging for troubleshooting. Use the policy names and configuration details in Microsoft’s current KB article, then apply policy and restart as required by your organization’s management tooling.
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Group Policy is preferable to ad-hoc registry editing in an enterprise because it can be documented, scoped and rolled back centrally. Logging is especially useful when a device still cannot enable SAC after the restoration policy is applied.
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What is and is not affected
| Device state before KB5127648 | Expected result | Action |
|---|---|---|
| SAC already enabled | Remains protected by SAC under this specific issue | Continue normal monitoring; no workaround is required solely for this bug |
| SAC was turned off and the switch is grayed out or fails | May be unable to re-enable SAC | Use Microsoft’s two registry overrides, or the two special Group Policies for managed PCs |
| SAC was never available because of compatibility or policy conditions | Not necessarily related to KB5127648 | Check device policy, SAC eligibility and application requirements |
This distinction matters: SAC’s protection behavior and the ability to turn it back on are separate questions. The confirmed regression targets re-enabling SAC after it was disabled.
Permanent fix status
Microsoft says it is working on a resolution for a future release, but the checked KB5127648 page does not identify the release number or date. Keep the mitigation in place if it is needed, and monitor the KB5127648 release notes for Microsoft’s resolution before removing registry or policy settings.
Quick Recap
If the workaround does not work
- Confirm that KB5127648 is installed and that SAC had previously been turned off.
- Recheck the exact registry path, value names, data type and value
1; run the commands from an elevated prompt. - Restart after both commands, then recheck the Windows Security path.
- On a work-managed PC, check whether domain, MDM or local policy is overriding the setting; use the enterprise policies and logging option instead of mixing unmanaged edits.
- If SAC is still unavailable, treat compatibility or policy restrictions as a separate diagnosis and wait for Microsoft’s documented fix rather than assuming every grayed-out switch is caused by KB5127648.
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