May or May Not...
The alert – privately circulated today by the FBI's InfraGard program – claims hackers may or may not be able to take over a plane's navigational system via the in-flight entertainment (IFE) system or public Wi-Fi network.
The only reason for there being any doubt in the matter is if there is some sort of electronic connection between the IFE and the flight control systems, and it relies on firewalls, protocols, etc. (and not air gaps) to prevent a hack taking place.
The only reason that connection exists is because the manufacturers wanted to do that (and were allowed to by the regulators [FAA, CAA, etc]), because it was cheaper. Penny pinching.
If the regulators had said no, they must be air-gapped, there would be absolutely no doubt at all. A hack would clearly be impossible via a seat IFE port.
Instead we have a situation where no one can really say for sure whether there is a problem or not. The people charged with keeping us safe are always going to 'er' on the side of caution. Meanwhile the people who can answer the question aren't going to be allowed to do so. That's because the law enforcement guys know damned well that if the answer is yes, a hack is feasible, that knowledge will leak out. And if that happens then chaos will ensue.
Law enforcement types might try and find the answer themselves, but they'd need a huge amount of extra resources. And they might just discover that the dreaded answer is 'yes', the knowledge that no one wants to have. And the worst is that they might never be totally sure of a 'no' answer.
This is a totally predictable outcome stemming from a poor design choice made by manufacturers seeking to save a few dollars / euros, and it's going to cost us millions. Already has in fact. Some aged retired avionics engineer somewhere (not me) is sat at home right now feeling somewhat vindicated and smug, and contemplating phoning his old boss to say, "told you so, you prick".
Pound foolish idiots.