Recent Windows Server updates cause errors in Hyper-V VMs

• Microsoft has issued a warning about its latest December Patch Tuesday updates causing errors when creating virtual machines on Hyper-V hosts.
• The existing VMs with existing network adapters do not have connection issues after installing the update and the affected platforms are Windows Server 2022 and Windows Server 2019.
• Windows engineers are currently working on the patches which will be released in an upcoming release.

Microsoft informed that the latest Windows Server updates cause failures during the creation of virtual machines on Hyper-V hosts. Apparently, the glitches only happen in Windows Server and AzStack HCI hosts managed in software-defined networking (SDN) environments with System Center Virtual Machine Manager (SCVMM).

Affects only new VMs

Microsoft says the error exists in Windows Server/AzStack HCI hosts in SDN-enabled environments that are managed using System Center Virtual Machine Manager (SCVMM). And users might receive an error in efforts to create a new Network Adapter joined to a VM network or a new Virtual Machine with a Network Adapter joined to a VM network. Windows said;

« After installing KB5021249 on Hyper-V hosts managed by Software Defined Networking (SDN) configured System Center Virtual Machine Manager (VMM), you might receive an error on workflows involving creating a new Network Adapter (also called a Network Interface Card or NIC) joined to a VM network or a new Virtual Machine (VM) with a Network Adapter joined to a VM network. »

Windows states the existing VMs with existing network adapters won’t have connection issues after installing the update. Only new network adapters created after installing KB502129 will be affected. The company named the affected servers as Windows Server 2022 and Windows Server 2019.

Workaround

The company’s engineers are working on a fix for the error and it will be included in an upcoming release. Until then, the company has developed a workaround.

Users can open an elevated PowerShell window on all SCVMM-managed Hyper-V hosts by hitting the Start button and typing “powershell” and then right-clicking or long pressing on it. They can then select “Run as Administrator” and run the following commands:

lang = (Get-WinSystemLocale).Name
C:\Windows\system32\wbem\mofcomp.exe C:\Windows\system32\wbem\$lang\VfpExt.mfl
C:\Windows\system32\wbem\mofcomp.exe C:\Windows\system32\wbem\VfpExt.mof

Additionally, the users can find a script for the workaround for large-scale deployments and a post-install script to be integrated with patching tools. The scripts are available here.