CVE-2019-12929

QEMU’s Machine Protocol (QMP) is designed to enable remote applications (ex. Libvirt) to control and manage QEMU process instances. QEMU Guest-Agent is a daemon program which helps remote applications (ex. Libvirt) to run commands on the guest VM, it supports QMP commands. It is meant to be used by trusted users and applications. The TCP server socket is only one of the transport options supported by QMP; other, more secure options, being local UNIX socket. If one is able to run QEMU Guest Agents’ ‘guest_exec’ command, the user already has access to the guest VM. Then sending guest state to an unworthy remote machine via nc is not really a security issue. Libvirt only uses local UNIX sockets to interact with the guest VMs that it manages. This UNIX socket is owned by the same user-id as the QEMU process instance. Other users on the system cannot connect to the UNIX socket. Libvirt also creates a unique per-VM sVirt label so VMs cannot access each other’s UNIX sockets, even though they are owned by the same system user-id.