The kernel driver should have parsed the update, or at a minimum it should have validated a signature, before trying to load it.
There should not have been a mechanism to bypass Microsoft’s certification.
Microsoft should never have certified and signed a kernel driver that loads code without any kind signature verification, probably not at all.
Many people say Microsoft are not at fault here, but I believe they share the blame, they are responsible when they actually certify the kernel drivers that get shipped to customers.