A flaw in the interaction between OpenStack Nova and the `qemu-img` utility allows an authenticated user to overwrite arbitrary files or destroy data on the compute host. The issue occurs when Nova's Flat image backend invokes `qemu-img` without strictly constraining the disk image format. An attacker can exploit this by writing a malicious QCOW header to a root or ephemeral disk and triggering a resize operation. This vulnerability specifically affects compute nodes using the Flat image backend, typically those configured with `use cow images` set to `False`.