NIST has published Special Publication (SP) 800-125A, Security Recommendations for Hypervisor Deployment on Servers. A hypervisor is a collection of software modules that provides virtualization of hardware resources, enabling multiple computing stacks called Virtual Machines (VMs) to be run on a single physical host. 

The security recommendations in this document relate to ensuring the secure execution of baseline functions of the hypervisor, when deployed for the purpose of server virtualization (but not for other use cases such as embedded systems or desktops). Recommendations for secure configuration of a virtual network are dealt with separately in SP 800-125B.