No Docker unprivileged containers are absolutely secure. No matter what you always have to be thinking about security. If you know the potential attack vectors for any system, process or application is key to its defence. At this time there are no known critical vulnerabilities for Docker’s container implementation at least not anything specific to Docker not present in containers in general. Perhaps it does not mean that there are undiscovered vulnerabilities or that such won’t be introduced in future releases. If you want to learn Docker then I would suggest you must take up the following Docker training course. I am also mentioning a video tutorial which you must watch to learn all the basic stuff regarding Docker.