January’s Patch Tuesday left many Windows Server admins in a very bad place: domain controllers in boot loops, unavailable ReFS volumes, and Hyper-V refusing to start.
BleepingComputer reports that admins described domain controllers on all versions of Windows  entering boot loops as the LSASS.exe process consumed all CPU resources and crashed the system, which automatically then restarted.
It also notes that, at least on Windows Server 2012 R2, the Hyper-V hypervisor will not start, which causes virtual machine launches to fail. It says other unverified reports have reported the problem on newer versions of Windows Server.
The third issue is that Windows Resilient File System (ReFS) volumes are no longer accessible or are seen as RAW (unformatted) after installing the updates. NTFS volumes are not affected.
So far, the only fix for these issues is to uninstall the entire update package, removing not only the problem fixes, but any security updates also included in it.
Microsoft says it is aware of the issues and is investigating.
Update: BleepingComputer now reports that the company has pulled the updates; they are KB5009624 for Windows Server 2012 R2, KB5009557 for Windows Server 2019, and KB5009555 for Windows Server 2022.
We will update this story when further information is available.
