Microsoft Defender Won't Open on Windows 11 – Error 0xC0000005 (MicrosoftSecurityApp.exe)

Ignacio Gobantes Carrasco 0 Reputation points
2026-11-10T00:51:41.4766667+00:00

Hello everyone,

I'm experiencing a persistent issue with the Microsoft Defender app included with my Microsoft 365 subscription, running on Windows 11, version 26H2.

Initially, the application displayed an error when I tried to sign in with my Microsoft account. Shortly afterward, it stopped launching altogether. Now, whenever I try to open Microsoft Defender from the Start menu or Microsoft Store, absolutely nothing happens. No window appears, and no error message is displayed.

Errors recorded in Windows Event Viewer:

  • Faulting application: MicrosoftSecurityApp.exe

Application version: 1.2.2608.18002

Exception code: 0xC0000005 (Access Violation)

Event ID 1000: Application Error

Event ID 1026: .NET Runtime – Unhandled Exception

Troubleshooting steps I have already tried:

Uninstalled and reinstalled Microsoft Defender from the Microsoft Store.

Reset the application using PowerShell (Reset-AppxPackage).

Re-registered the application package using Add-AppxPackage.

Ran DISM /Online /Cleanup-Image /RestoreHealth and sfc /scannow. Both completed successfully, and SFC reported no integrity violations.

Performed a clean boot of Windows, temporarily disabling third-party services and startup applications.

Created a new Windows user account and attempted to launch Microsoft Defender from that account. The application still would not open.

Initiated a Windows 11 repair installation through Windows Update. The computer subsequently restarted, but the issue persisted. I have not been able to confirm whether the repair installation completed successfully.

Verified through PowerShell that the Microsoft Defender application package is installed and reports a status of Ok.

Microsoft Defender Antivirus status:

I also ran Get-MpComputerStatus in PowerShell and confirmed the following:

AntivirusEnabled: True

RealTimeProtectionEnabled: True

Therefore, the built-in Microsoft Defender Antivirus engine and real-time protection are working correctly. The issue appears to affect only the separate Microsoft Defender app included with Microsoft 365.

My questions are:

Has anyone experienced this specific 0xC0000005 access violation involving MicrosoftSecurityApp.exe?

Is there a known compatibility issue, dependency problem, or application-specific fix that could explain this behavior?

Most importantly, is there a way to resolve the issue without performing a full Windows reinstall or losing my installed applications, personal files, and settings?

I would particularly appreciate suggestions beyond the troubleshooting steps listed above, as none of them has resolved the problem.

I can provide Event Viewer screenshots and additional diagnostic information if needed.

Thank you in advance for your help.

Microsoft 365 and Office | Microsoft 365 Defender | For home | Windows
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  1. Xavier-D 14,530 Reputation points Microsoft External Staff Moderator
    2026-11-11T01:57:08.6866667+00:00

    Hello Ignacio Gobantes Carrasco,

    Thank you for providing such a detailed description and for listing everything you have already tried.

    Since Microsoft Defender Antivirus and real-time protection are still enabled, your device’s underlying antivirus protection appears to be operating. The crash seems to affect the separate Microsoft Defender app and its interface.

    You have already completed the usual repair steps, including testing another Windows account, so I would not recommend repeating them.

    Could you please confirm the following?

    • Your complete Windows version and OS build, shown under Settings > System > About
    • Whether the device is enrolled in the Windows Insider Program
    • Whether another antivirus or security application is currently installed, or was installed previously
    • In Event Viewer, the Faulting module name and Faulting module path from the MicrosoftSecurityApp.exe Event ID 1000 entry

    Because the same crash occurs in a newly created Windows account and continues after reinstalling the app, this may require investigation of the application crash rather than additional account-level troubleshooting.

    Please also report the crash through Feedback Hub > Apps > Microsoft Defender, include error code 0xC0000005, and attach the relevant Event Viewer details. If the device is not running an Insider build, you may also contact Microsoft Support so they can help collect and examine the crash diagnostics.

    Please do not post any dump files publicly, as they can contain system or account information.

    Feel free reply back to this post and update me on this issue, I'll be happy to help.

    Was this answer helpful?

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