This CIO article too addresses such issues:
I.T. managers worry that security attacks designed to exploit a hypervisor could infect virtual machines that reside on the same physical host, in what is known as a "virtual-machine escape".
If a virtual machine is able to "escape" the isolated environment in which it resides and interact with the parent hypervisor, industry experts say it's possible an attacker could gain access to the hypervisor, which controls other virtual machines, and avoid security controls designed to protect the virtual machine.
"The Holy Grail of security in the virtual world is to bounce out of the [virtual machine] and take control," says Pete Lindstrom, a senior analyst at Burton Group, in a recent webcast on virtualisation security.
But while there are documented attempts to execute a virtual-machine escape, some point out that a security disaster related to such an event has yet to be proved.
"To my knowledge, there has never been a hack that has allowed a security problem to propagate from one virtual host to another by way of the hypervisor technology," says Steve Ross, a consultant with Catapult Systems, which is helping logistics provider Transplace, based in Texas, deploy and maintain its VMware virtual environments.
Read it all on CIO Today