Problem after Windows Patch Day: Hyper-V Host no longer works

There are other issues related to patch-day Windows security updates. Users report that updates KB5009586 and KB5009624 for Windows Server 2012/R2 prevent Hyper-V host from starting. This leads to corresponding further problems. Reported on the Hyper-V difficulties after the recent patch day update.

It says that users of Microsoft’s Hyper-V should be careful when installing security updates KB5009586 (Monthly Rollup Update) and KB5009624 for Windows Server 2012/R2. Numerous affected people report that they can no longer start Hyper-V host after the security update. With that, the virtual machines are completely knocked out. VM won’t start anymore, the only error message you get is that the hypervisor is not running (“The virtual machine could not be started because the hypervisor is not running”). The reports from those affected are currently increasing rapidly, more and more users are reporting in the relevant forums and on Reddit to exchange information about the Hyper-V bug.

Uninstall updates

So far, however, there is no indication of the cause of the problem. Microsoft has not yet listed the bug as a known problem, which is not surprising given the closeness to patch day. However, it is currently not clear to what extent this is a widespread problem or whether only a few users are affected. We will now have to wait and see. Those affected report that they have uninstalled the security update as the only effective measure. Once the update is removed and the server restarted, everything works as expected again.

However, Microsoft warns against the exploitation of various vulnerabilities that – if the latest security patches are not installed – continue to make the systems vulnerable.