there have been a few xen hvm issues that allow user processes to bypass the VM kernel's normal memory protections, e.g. http://xenbits.xen.org/xsa/advisory-105

there have been a few xen hvm issues that allow user processes to bypass the VM kernel's normal memory protections, e.g. http://xenbits.xen.org/xsa/advisory-105.html http://xenbits.xen.org/xsa/advisory-105.html so the answer to your question is yes: there have been cases where simply adding the hypervisor introduced a vulnerability .