VT-x itself is not the main attack surface. It's all the interfaces between the inside and the outside of the VMs, for example graphics hardware emulation, netw

VT-x itself is not the main attack surface. It's all the interfaces between the inside and the outside of the VMs, for example graphics hardware emulation, network hardware emulation, etc. etc. There have been many of these bugs, on qubes/xen, and basically every other popular hypervisor. I have personally found a kernel memory disclosure vulnerability affecting xen, which I tested under qubes (it wasn't a very useful bug, but the point is, they exist and they are plentiful). Furthermore, the "blue pill" attack is not a vulnerability in VT-x itself. In fact, it does not exploit any vulnerabilities at all - it simply works off the idea that code running in ring n can hide itself from code running ring+1 (the bluepill hypervisor being ring -1).