In Xen, dom0 is the privileged control domain: the first and most trusted virtual machine, usually running the management tools and drivers that create, configure, and monitor other guests. Unlike a normal guest, dom0 has direct control over many host-side operations and often mediates device access, scheduling, and administrative actions.
This makes dom0 a critical security boundary. If an attacker compromises dom0, they may gain the ability to manage or inspect other guests, interfere with isolation, or alter the hypervisor’s control path. Defenders therefore treat dom0 as high-value infrastructure: it should be minimized, patched quickly, and restricted with strong access controls. In real environments, hypervisor or management-plane flaws often matter because they can affect dom0, turning an ordinary bug into a potential path to host compromise or cross-VM impact.