A guest VM is a virtual machine that runs on shared physical infrastructure under the control of a hypervisor or cloud platform. It behaves like an independent computer, but its CPU, memory, storage, and network access are mediated by the host environment. This isolation is a core security feature of virtualization: one tenant’s workload should not be able to directly touch another tenant’s systems or the underlying host.
In cyber security, the guest VM is both a protection layer and a source of attack traffic. Malware inside a guest can probe virtual devices, send malformed packets, or abuse shared interfaces to find flaws in the hypervisor, virtual NICs, or offload hardware such as a DPU. Defenders therefore treat guest-facing paths as trust boundaries. Hardening means patching virtualization components, minimizing exposed devices, validating guest input, and monitoring for abuse of virtual hardware features. A secure guest VM is isolated, but not automatically trusted.