A flaw was found in KubeVirt's network annotation generator. The tenant-supplied multus.networkName in a VMI spec is written verbatim into the launcher pod's v1.multus-cni.io/default-network annotation without input validation. When the ExternalNetResourceInjection Beta feature gate is enabled (off by default), no NAD lookup is performed to catch malformed values, and a tenant can inject a JSON-formatted NetworkSelectionElement array to attach the pod to arbitrary network attachments in any namespace with attacker-controlled IP and MAC addresses. This enables cross-namespace network access and service impersonation. The vulnerable code path was introduced with the ExternalNetResourceInjection feature gate in KubeVirt v1.8.0, first shipped in OpenShift Virtualization 4.21.