In what sense is this a “backdoor”? Seems to me the code is coming through the front door, which the victims left open.
DockerHub is just the delivery mechanism.
DockerHub is just the delivery mechanism.
From Kromtech's article I deduced that this only happens when a docker daemon (or kubernetes interface) is exposed to the Internet and an attacker uses that to download and start a docker image on the victim's host. Then they can bind mount a host directory like described and attack the host computer.