Please remember that VulnHub is a free community resource so we are unable to check the machines that are provided to us. Before you download, please read our FAQs sections dealing with the dangers of running unknown VMs and our suggestions for "protecting yourself and your network. If you understand the risks, please download!
Leave a message is a new anonymous social networking site where users can post messages for each other. They've assigned you to test their set up. They do utilize docker containers. You can conduct attacks against those too. Try to see if you can get root on the host though.