[German]May 2023 security updates for Windows 11 and Windows Server 2022 brought a nasty Explorer bug. Administrators can no longer query permissions for files in Explorer – the function hangs and leads to high CPU load. After I promptly addressed this issue here on the blog, Microsoft has now officially confirmed the bug.
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The Effective Access bug in Explorer
Here on the blog I've reported on May 27, 2023, in the blog post Windows: Patchday issues and fixes in May 2023 (Server 2022 effective access query, VPN) what administrators reported to me right after the May 2023 patchday. Windows Server 2022 cumulative update KB5026370 prevents Explorer from querying effective permissions. A German user described it as:
After installing the KB5026370 update, I can no longer query effective permissions via Windows Server 2022. Windows Explorer loads the CPU, but nothing happens. Has anyone else experienced this problem? Unpatched Server 2022 behaves correctly and as usual in that regard.
Another user confirms in this comment that he was able to reproduce the problem after reading a text. The bug affects Windows Server 2022 and Windows 11. Blog reader Tobias still posted a link to Microsoft's article Effective Access Query not responding on Windows Server 2022 , where I posted a backlink to my blog post with the bug description. Another user then submitted a support case to Microsoft.
Microsoft confirms the bug
In an entry Computing effective access might not show results, dated June 21, 2023, Microsoft has confirmed the bug in Windows 11 22H2 Release Health-Dashboard. There Microsoft writes:
After you install updates that were released on or after May 9, 2023, you might not be able to view effective access in the Advanced Security Settings dialog box for shared files or folders.
On affected devices, when you select the View Effective Access button, the message Computing effective access…. appears, but the results of the query might not be displayed and explorer.exe might continue to use the CPU after the Advanced Security Settings dialog box closes.
This problem occurs mainly in corporate environments (on consumer devices the feature is usually not used) and affects Windows 11 22H2 with update KB5026372, Windows 11 21H2 with update KB5026368, and Windows Server 2022 with update KB5026370 (see also).
Microsoft's developers are working on a solution and expect it to be available by the end of June 2023. Provided that someone runs into the problem, closes Explorer, but the CPU load remains high, Microsoft suggests restarting the device as a workaround. Alternatively, the affected user can be logged out (locking is not enough) to exit the shell. This should reduce the CPU load to the normal level again.
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