Simple definition
A VM escape is a security vulnerability that lets code in a guest cross the isolation boundary into the host or hypervisor.
Purpose and use
A VM escape is a compromise that crosses the intended boundary between a guest and its hypervisor or host environment.
How does it work?
It can exploit a vulnerability in a virtualization component exposed to the guest.
Example and verification
Assess affected versions, features and prerequisites in a security advisory before determining exposure.
Points to watch
Compromise inside a VM does not prove escape. Conversely, virtual isolation does not eliminate hypervisor vulnerabilities.
In short
Distinguish guest compromise from an actual crossing of the virtualization boundary.