Introduction to blockchain, gossip protocols, and common attack vectors.

Thus, it is possible for an adversary miner to attempt to continue building blocks on top of the existing chain (in stealth mode) so they can build a chain longer than the current true and legitimate one (even if it’s by one or two blocks).
Once they have done that, they will publish their private fork, which will be falsely be accepted as the true chain since it is the longest. The adversary can then proceed to conduct transactions in the network, just before publishing their longer stealth chain to reverse the transaction they just did. This malicious behavior allows for a small window in which a double-spending attack is possible.

Timejack attack

Nodes in some blockchain networks are depended on internal timing taken from the median time the peer nodes report.

In a Timejack attack, an adversary attempts to manipulate the time by injecting a lot of malicious nodes in the network. This is especially easy in an Eclipse attack. This attack will mean that the victim node be unable to accept blocks from the actual network as the timestamp of the blocks will not be in line with its timestamp, also it means that the victim’s node cannot be broadcasted to the actual blockchain network. This attack can cause double spending to be conducted

Finney attack — is when an adversary mines a block with one of the victim’s transactions and keeps it in stealth mode.
When another miner accepts the unconfirmed transaction, the adversary transfers them the earlier transacted transaction. This is done by the adversary publishing the earlier mined block (that has been kept in stealth mode) before the new transaction is confirmed on the network. This makes double-spending possible.

A race attack is a variant of the Finney attack.
The only difference is that the adversary doesn’t need to pre-mine the block with their transaction, to conduct double-spending. Instead, the adversary submits an unconfirmed transaction to a merchant, and at the same time, the adversary transmits another transaction that they broadcast to the blockchain network.
This tricks the merchant, into believing their transaction is the first, but in reality, this is never submitted to the blockchain network by the adversary. For this attack to occur, the adversary needs to be directly linked to the merchant.