https://www.bleepingcomputer.com/news/security/escaping-containers-to-execute-commands-on-play-with-docker-servers/

Improperly secured privileged containers on the Play with Docker testing platform offered security researchers a way to escape Linux containers and run arbitrary code on the host system.

An attacker successfully exploiting the flaw would have had high-level access to the Play with Docker (PWD). They would also have been able to access all running containers.