Docker is comparable to a chroot in this regard. You can not break out of a chroot either, unless you are being careless with super user privileges or bind moun

Docker is comparable to a chroot in this regard. You can not break out of a chroot either, unless you are being careless with super user privileges or bind mounts. Which (unsuprisingly) people are, and that's why it's generally not recommended to use chroot alone for security. Not because chroot somehow is insecure or doesn't work as intended. Docker for the longest time didn't even try to constrict the root user. Later versions does, but the results will vary depending on your configuration. That's why the Docker documentation states it should not be depended on for security. It is wise to heed that recommendation.