This is near to impossible, maybe the attacker can broadcast transaction that are already spent in the real largest chain.
It is possible to broadcast any transaction. What's impossible is to "fake" a transaction if it isn't against the protocol rules. Double-spending a transaction doesn't count as "faking" if you redo the work.Unless the isolated node is mining there is no use of doing fake tx, even if it was mining, it wouldn't accept a fake tx unless you feed it with a fake longest chain
There is no "fake longest chain", no matter how much we'd want it. There is the difficultywise-longest chain, and it's always the correct chain. If another one comes up, with more work, that becomes the correct one. What is needed to be emphasized is that an eclipse attack isn't going to be effective if the attacker doesn't spend a significant amount of resources to redo the Proof-of-Work, which in that case, the network would be under threat anyway. The reason is that the attacker must maintain an entire chain themselves. If your node receives no blocks for hours, or days, you can make out you're under an eclipse attack. The attacker must solve blocks every 10 minutes to go unnoticed, which requires to redo a lot of work. They cannot re-create their own, little-worked chain, because node software comes with checkpoints.
That is my understanding as to why an eclipse attack shouldn't be concerning, but please correct me if I'm wrong.
