So this is how it was done 25 years ago: Only the used ports (ethernet jacks) on a network is activate, disconnecting a device and the port closes. That strictly speaking doesn't mean that there aren't way to get devices on the network, but it does make it a lot harder. You're absolutely correct about these networks being in hostile environments, but why then do we pretend that they are not? Fridges like these have never not been in a hostile environment, so why aren't basic security measures taken to secure the physical side of things?
In my world the central server can be hack in two ways, that is by a malicious operator or via some scheme like the US/Israeli attack on Irans uranium centrifuges. The central server also have no business being online, that to is on a closed network, running the whitelisted applications from the manufacturer.
In my world the central server can be hack in two ways, that is by a malicious operator or via some scheme like the US/Israeli attack on Irans uranium centrifuges. The central server also have no business being online, that to is on a closed network, running the whitelisted applications from the manufacturer.