0x-r4bbit / simple-reentrancy-attack

A demo repository showing a simple reentrancy attack

Simple reentrancy attack

A simple reentrancy attack demonstration

There are two contracts in this repo:

1. VulnerableContract - To deposit and withdraw funds
2. AttackerContract - To perform reentrancy attack

The attack can be executed by changing

function withdraw(uint256 amount) external {
  require(balances[msg.sender] >= amount, "Insufficient balance");
  (bool success, ) = msg.sender.call{value: amount}("");
  require(success, "failed call");
  balances[msg.sender] -= amount;
}

in VulnerableContract to:

function withdraw(uint256 amount) external {
  require(balances[msg.sender] >= amount, "Insufficient balance");
  (bool success, ) = msg.sender.call{value: amount}("");
  require(success, "failed call");
  unchecked {
    balances[msg.sender] -= amount;
  }
}

Executing the attack

Run

$ forge test -vvv

Verbosity level option is used to get execution traces.