Windows 10: New bug hits popular built-in security features

Windows Sandbox and Windows Defender Application Guard fail to open on Windows 10 version 1903 and newer.

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Microsoft says it is working on a fix for an error that prevents Windows Sandbox and Windows Defender Application Guard from opening. 

The issue affects Windows 10 versions 1903, 1909, and 2004. When failing to open, the bug triggers the error message 'ERROR_VSMB_SAVED_STATE_FILE_NOT_FOUND (0xC0370400)' or 'E_PATHNOTFOUND (0x80070003)'.

Windows Sandbox is a relatively new feature of Windows 10 Pro and Enterprise editions since version 1903 that lets users launch a virtual machine with a basic version of Windows 10 to run potentially suspicious software without the risk of it affecting the main Windows 10 installation. 

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The feature has proved popular with IT pros because of its ability to safely run potentially risky executables in a container, and Microsoft included several improvements to Windows Sandbox in Windows 10 version 2004.   

Windows Defender Application Guard (WDAG) is also a relative newcomer in Windows 10 Pro and Enterprise editions that admins can use to create a list of trusted websites and local resources. 

WDAG comes into play when users access a URL outside that list. It launches Microsoft Edge in a Hyper-V container to keep the browser isolated from the operating system. Microsoft released WDAG extensions for Chrome and Firefox last year.   

"To mitigate this issue after receiving one of the above error messages, you will need to restart your device," Microsoft explains in a support note

Microsoft plans on addressing the bug in an upcoming release of Windows 10. However it hasn't said when the fix is expected to arrive. 

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The company hasn't listed the issue on its Windows release health dashboard for any of the affected versions, which may be because there is a simple workaround.

As Bleeping Computer notes, a similar issue affected Windows Sandbox on Windows 10 Insider previews last year after users installed the KB4497936 update.