Can One Virtual Machine Compromise the Security of Another?

One of the frequently mentioned benefits of VPS hosting is that it is more secure than shared hosting because your account is walled off from other accounts, allowing them to function as separate servers. Virtual private servers and virtualization in general are generally thought to be secure. So, can one virtual machine compromise the security of another? Is that even possible?

The short answer is: yes. It is possible, at least in theory. The long answer, however, involves digging a little deeper. First, it is important to understand that a virtual machine, no matter how much it appears to operate independently, is still ultimately dependent on its host machine. Therefore, if the host machine is in any way compromised, all of the virtual machines running on it could be at risk. Therefore, the real question is not whether one virtual machine can affect another but if it is possible for a virtual machine to affect the host.

Over time, there have been a few exploits, such as one for Xen hypervisor, that allowed an attacker operating within a virtual machine to “escape” into the larger host system, and another for VMware products running on Windows systems that allowed for a similar privilege escalation.

These exploits are largely theoretical since they may not have ever actually been used for attacks, and once discovered, the developers fixed the problems. The salient point here is that such attacks are possible, and you should therefore make sure your virtualization software stays updated and has standard security measures in place.