Blockchain Technology and Vulnerability Exploits on Smart Contracts

The immutability of smart-contract characteristics is a significant key benefit of blockchain. However, after we deploy a smart contract in a blockchain, we cannot change, modify, or debug it. Further, wrong or vulnerable coding implementation in smart contracts could have error output that may have severe consequences in the future. Thus, the challenge of finding vulnerabilities in the smart contract is vital to stop criminals from performing malicious exploits during Defi transactions. The paper explores Blockchain Technology in Smart Contracts to detect vulnerability exploits focused on general purchase agreements and smart contracts. The novelty contributions of the paper are threefold: First, we explore the existing blockchain vulnerabilities and how attackers exploit decentralized financial transactions (Defi), including re-entrancy attacks, 51% attacks, and double spending issues. Secondly, we set up a Remix virtual platform using the solidity tool to demonstrate a purchase agreement between client and seller that can interact in a smart contract to determine how it can be exploited. The implementations show how the attacker can call the withdraw function recursively before the transaction updates the balance during transaction procedures. Finally, we recommend control mechanisms to improve blockchain security in the purchase agreement and re-entrancy attacks. Our results show that re-entrancy attacks and purchase agreement smart contracts can be secured by developing modifiers to update the bank balance before completing transactions.