alt Hacker News> This still shouldn't be online.
This line suggests the units themselves were targeted individually with a hack:
> Danfoss said the affected cold units were older models whose security software could not be updated to ward off a risk they had identified.
But the problem with networked devices spread across tens of thousands of pretty much unguarded locations, surrounded by unvetted employees, but taking orders form a central location is that there is no such thing as "not online". They'll talk to the management server used to set up the nightly defrost schedules across the fleet. Even if they are in an isolated VLAN, it's always one step away from someone connecting a Pi to that network and off they go online. There's only so much zero-trust, NAC/802.1x and segmentation can do when some devices will be too old to support these and their network will be the entry point to the management server, then to the whole fleet.
I'm honestly very surprised that a couple of things things haven't happened yet: the central server for managing these fleets getting hacked and allowing access to the entire fleet, and/or the companies realizing that the only way to limit the reach of an attack is to physically not have the hardware needed to do remote control.
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.