It was discovered that vzctl, a set of control tools for the OpenVZ server virtualisation solution, determined the storage layout of containers based on the presense of an XML file inside the container. An attacker with local root privileges in a simfs-based container could gain control over ploop-based containers. Further information on the prerequites of such an attack can be found at https://src.openvz.org/projects/OVZL/repos/vzctl/commits/9e98ea630ac0e88b44e3e23c878a5166aeb74e1c The oldstable distribution is not affected.