Containers must not map to privileged ports.

Privileged ports are those ports below 1024 and that require system privileges for their use. If containers are able to use these ports, the container must be run as a privileged user. MKE must stop containers that try to map to these ports directly. Allowing nonprivileged ports to be mapped to the container-privileged port is the allowable method when a certain port is needed. An example is mapping port 8080 externally to port 80 in the container.

By default, if the user does not specifically declare the container port to host port mapping, MKE automatically and correctly maps the container port to one available in 49153-65535 block on the host. But, MKE allows a container port to be mapped to a privileged port on the host if the user explicitly declared it. This is because containers are executed with NET_BIND_SERVICE Linux kernel capability that does not restrict the privileged port mapping. The privileged ports receive and transmit various sensitive and privileged data. Allowing containers to use them can bring serious implications.