When people talk about a blockchain attack, the 51% attack is most often mentioned. It is usually said that the attacker must gain dominance over the resource that is used in the given network consensus. That should be costly. However, the attacker does not always have to buy the resource directly. What if the resource can be obtained through social engineering, for example, or by hacking several computers?
Read the article: https://cexplorer.io/article/how-to-attack-blockchain-cheaply