Bitcoin Core has several options for how to treat peers that violate the rules of the P2P protocol:
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Ignore the individual message, but continue processing other messages from that peer
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Increment the peer’s "misbehaviour" score, and punish the peer once its score goes above a certain amount
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Disconnect from the peer
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Disconnect from the peer and prevent any later connections from that peer’s address (discouragement)
Since PR#20079 we now treat handshake misbehaviour like an unknown message