This afaik only happens if the UTXO was already spent in a previous block, i.e. the "spending transaction" was already confirmed by a miner. The real difficulty for nodes is to know to order double spends occurring in the same block. Let's imagine we have transaction X spending the same UTXO than transaction Y, and both are created only few milliseconds one after another. Let's say the person trying to double spend wants to damage a person or service in Australia who accepts 0-confirmation transactions, so they broadcast transaction X targeting specifically several nodes in Australia, hoping that the victim sees it first. At the same time they broadcast double spend Y to nodes close to many mining pools, e.g. in the US. So the Australian potential victim node "sees" transaction X and discards transaction Y, but most US miners do the opposite and include transaction Y instead, because they didn't see in their UTXO set that transaction X happened (as it is still unconfirmed and they received it after transaction Y). As this is something that can happen all the time due to the latency between different networks (and more so if they're far away one from another, like in the example) I believe nodes won't ban another node for trying to broadcast an unconfirmed double spend. They simply check if the transaction is consistent with their own UTXO set, and if not, they discard it. Of course this "attack" is very unlikely to succeed, because it is unlikely that somebody really accepts a 0 confirmation transaction, and latency issues tend to improve with network speed. But it shows that the "chain state" and thus the "UTXO set" are always a local phenomenon, and all nodes manage it independently. This means in double spend cases nodes can't really see which transaction is the "valid" one, until a miner includes and thus confirms one of both transactions.
This afaik only happens if the UTXO was already spent in a previous block, i.e. the "spending transaction" was already confirmed by a miner. The real difficulty for nodes is to know to order double spends occurring in the same block. Let's imagine we have transaction X spending the same UTXO than transaction Y, and both are created only few milliseconds one after another. Let's say the person trying to double spend wants to damage a person or service in Australia who accepts 0-confirmation transactions, so they broadcast transaction X targeting specifically several nodes in Australia, hoping that the victim sees it first. At the same time they broadcast double spend Y to nodes close to many mining pools, e.g. in the US. So the Australian potential victim node "sees" transaction X and discards transaction Y, but most US miners do the opposite and include transaction Y instead, because they didn't see in their UTXO set that transaction X happened (as it is still unconfirmed and they received it after transaction Y). As this is something that can happen all the time due to the latency between different networks (and more so if they're far away one from another, like in the example) I believe nodes won't ban another node for trying to broadcast an unconfirmed double spend. They simply check if the transaction is consistent with their own UTXO set, and if not, they discard it. Of course this "attack" is very unlikely to succeed, because it is unlikely that somebody really accepts a 0 confirmation transaction, and latency issues tend to improve with network speed. But it shows that the "chain state" and thus the "UTXO set" are always a local phenomenon, and all nodes manage it independently. This means in double spend cases nodes can't really see which transaction is the "valid" one, until a miner includes and thus confirms one of both transactions.

This afaik only happens if the UTXO was already spent in a previous block, i.e. the "spending transaction" was already confirmed by a miner. The real difficulty for nodes is to know to order double spends occurring in the same block. Let's imagine we have transaction X spending the same UTXO than transaction Y, and both are created only few milliseconds one after another. Let's say the person trying to double spend wants to damage a person or service in Australia who accepts 0-confirmation transactions, so they broadcast transaction X targeting specifically several nodes in Australia, hoping that the victim sees it first. At the same time they broadcast double spend Y to nodes close to many mining pools, e.g. in the US. So the Australian potential victim node "sees" transaction X and discards transaction Y, but most US miners do the opposite and include transaction Y instead, because they didn't see in their UTXO set that transaction X happened (as it is still unconfirmed and they received it after transaction Y). As this is something that can happen all the time due to the latency between different networks (and more so if they're far away one from another, like in the example) I believe nodes won't ban another node for trying to broadcast an unconfirmed double spend. They simply check if the transaction is consistent with their own UTXO set, and if not, they discard it. Of course this "attack" is very unlikely to succeed, because it is unlikely that somebody really accepts a 0 confirmation transaction, and latency issues tend to improve with network speed. But it shows that the "chain state" and thus the "UTXO set" are always a local phenomenon, and all nodes manage it independently. This means in double spend cases nodes can't really see which transaction is the "valid" one, until a miner includes and thus confirms one of both transactions.

This afaik only happens if the UTXO was already spent in a previous block, i.e. the "spending transaction" was already confirmed by a miner. The real difficulty for nodes is to know to order double spends occurring in the same block. Let's imagine we have transaction X spending the same UTXO than transaction Y, and both are created only few milliseconds one after another. Let's say the person trying to double spend wants to damage a person or service in Australia who accepts 0-confirmation transactions, so they broadcast transaction X targeting specifically several nodes in Australia, hoping that the victim sees it first. At the same time they broadcast double spend Y to nodes close to many mining pools, e.g. in the US. So the Australian potential victim node "sees" transaction X and discards transaction Y, but most US miners do the opposite and include transaction Y instead, because they didn't see in their UTXO set that transaction X happened (as it is still unconfirmed and they received it after transaction Y). As this is something that can happen all the time due to the latency between different networks (and more so if they're far away one from another, like in the example) I believe nodes won't ban another node for trying to broadcast an unconfirmed double spend. They simply check if the transaction is consistent with their own UTXO set, and if not, they discard it. Of course this "attack" is very unlikely to succeed, because it is unlikely that somebody really accepts a 0 confirmation transaction, and latency issues tend to improve with network speed. But it shows that the "chain state" and thus the "UTXO set" are always a local phenomenon, and all nodes manage it independently. This means in double spend cases nodes can't really see which transaction is the "valid" one, until a miner includes and thus confirms one of both transactions.