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I can finally reveal some research I've been involved with over the past year or so.
We (@redford@infosec.exchange, @mrtick@infosec.exchange and I) have reverse engineered the PLC code of NEWAG Impuls EMUs. These trains were locking up for arbitrary reasons after being serviced a...
A polish hacker found out why trains did stop working. The manufacterer implemented a hidden electronic switch, which automatically activated after trains were serviced by a different company.
The trains also had a GSM telemetry unit that was broadcasting lock conditions, and in some cases appeared to be able to lock the train remotely.
So, it sounds like this remote lock is speculation, so I'm not gonna say that this is actually the case here, and I don't know how trustworthy the source here is.
But, speaking in general: an additional problem with sticking back doors in products is that someone else may discover them and exploit them, and the uses to which they may put them may be considerably less-pleasant than whatever the purpose that the manufacturer had in sticking them in.
Just earlier this year, we had articles about this incident with Polish trains. That wasn't a back door in that it wasn't particularly hidden, but it was a way to do remote radio control of Polish trains, and sure enough, when someone who wanted to create trouble with it discovered it, it got used to cause problems for Polish train operators.
The Cheap Radio Hack That Disrupted Poland’s Railway System
The sabotage of more than 20 trains in Poland by apparent supporters of Russia was carried out with a simple “radio-stop” command anyone could broadcast with $30 in equipment.
It wasn't a back door, it was a safety feature working as designed. IIRC it didn't have any modern security implemented, because it's very old.
Also, the link from the OP doesn't mention that, but the trains in this story had locations of competitors' repair centers coded in, and were apparently set to auto-lock if they detected sitting in one for more than 10 days...
So, locking out repairs for anything they would have to order parts for.
I'm guessing that they're using some sort of custom size for their bolts and tolerances in the train. The competitors likely have the standard sizing for parts on hand, and any custom part would need to be ordered in. Likely from the same supplier.
Since they know their supplier's order return timing, they can set up the kill switch when they know that the train will be sitting in a yard awaiting parts.
Scummy as fuck.
it worked like this: public tenders for trains and its servicing are separate. at first, newag claimed that service documentation is their super secret IP and they can't disclose it. european railway authority however basically said that no, fuck you, you as a manufacturer have to disclose it. so they did, it's a 20k page thick book, and now other workshops (with all certs and so on) can compete in tender. while monopoly lasted, they could call whatever price they wanted and operators would pay anyway. smaller workshops just outcompeted them because they don't have dozen c-suite to pay
newag of course didn't like it and there comes the fuckery. what they did, among others, is they put logic that would prevent DC-AC converters from turning on if train spends 10d+ in one of hardcoded areas, these places being competing workshops. another mysterious thing was gsm modem that could (possibly) brick train remotely in the same way. later corporate would just claim that no one else can fix these trains, call competition unqualified, and grab severely overpriced servicing contracts. that is, until somebody actually looked inside. mechanically and electrically train was fully working, but it was just locked by software
