runc through 1.0-rc6, as used in Docker before 18.09.2 and other products,
allows attackers to overwrite the host runc binary (and consequently obtain
host root access) by leveraging the ability to execute a command as root
within one of these types of containers: (1) a new container with an
attacker-controlled image, or (2) an existing container, to which the
attacker previously had write access, that can be attached with docker
exec. This occurs because of file-descriptor mishandling, related to
/proc/self/exe.