I am studying consensus algorithm. In the case of the proof-of-work algorithm, a double spending attack was possible by the miner making a transaction and presenting the longest block from which the transaction was missing through 51% hash power. So, most of the transactions seem to pass the confirmation time and confirm the transaction.
The proof-of-authority algorithm provided by Ethereum allows only verified nodes to participate in consensus. Then, I think that the confirmation time will be lost in terms of transaction finalization.
Then.. In proof-of-authority, if a specific node is malicious, what are possible attack scenarios?
((For example, is it possible for an attack to allow two transactions with the same nonce for a specific account to exist on the blockchain?