Smart Contract Vulnerabilities Unveiled: Reentrancy Attack

Smart contracts are the backbone of decentralized applications on the blockchain. However, like any code, they can be vulnerable to attacks. One of the most notorious vulnerabilities is the reentrancy attack. In this article, we’ll delve into what reentrancy attacks are, provide examples of vulnerable code, and explain how to mitigate this risk.

What is a Reentrancy Attack?

A reentrancy attack occurs when a smart contract calls an external contract before updating its state. This allows the external contract to call back into the original function, potentially multiple times, before the original function has completed its execution. This can lead to unexpected behaviors and exploitation of the smart contract.

Vulnerable Code Example

Consider the following example of a vulnerable smart contract written in Solidity:

pragma solidity ^0.8.0;

contract VulnerableBank {
    mapping(address => uint) public balances;

    function deposit() public payable {
        balances[msg.sender] += msg.value;
    }

    function withdraw(uint _amount) public {
        require(balances[msg.sender] >= _amount, "Insufficient balance");
        (bool success, ) = msg.sender.call{value: _amount}("");
        require(success, "Transfer failed")…