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I'm pretty sure that I understand how replay attacks work: A malicious node takes a valid transaction from chain A, and replays it on chain B. Other nodes on chain B see the transaction as valid and therefore it is included in both chains, instead of just A.
My question is whether the first transaction in a block, that generates new bitcoins, can be also replayed.
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Short answer: No.
Longer answer: depends on the rules of the B chain.
A coinbase transaction creates coins out of thin air, but is typically only valid if the block itself is valid. Typically if the block is valid on chain A it's not valid on chain B: because a block usually points to it's previous block, which should be on the same chain.
On the other hand, the rules of B chain can literally be anything, as crazy as the creators imagination allows. If the B chain is specifically designed to also allow A blocks, then the answer would be yes. But the coins would still belong to the miner, so it's hardly an attack.
So what makes coinbase transactions impossible to replay, as opposed to regular tx's, is that they come together with a block, and that block is typically illegal on chain B. – Nathan_ – 2017-10-15T19:58:53.537
Yes. And if it were accepted on chain B, that money is still owned by the miner who has the private key to that coinbase address. Hardly an attack. – Jannes – 2017-10-16T03:11:03.067
2Are you literally asking if a coinbase transaction from one chain can be used as a coinbase in a block on the other chain? Under certain assumptions, yes, but it's pointless to do so: if you mine a block using a "replayed" coinbase you are just donating your block reward to the previous miner. It hurts the "attacker" and benefits the "victim". – Nate Eldredge – 2017-10-15T20:00:13.520