Token - The Ethernaut - Writeup

Wed, 22 Apr 2026 00:00:00 +0000

The goal of this level is for you to hack the basic token contract below.

You are given 20 tokens to start with and you will beat the level if you somehow manage to get your hands on any additional tokens. Preferably a very large amount of tokens.

// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

contract Token {
    mapping(address => uint256) balances;
    uint256 public totalSupply;

    constructor(uint256 _initialSupply) public {
        balances[msg.sender] = totalSupply = _initialSupply;
    }

    function transfer(address _to, uint256 _value) public returns (bool) {
        require(balances[msg.sender] - _value >= 0);
        balances[msg.sender] -= _value;
        balances[_to] += _value;
        return true;
    }

    function balanceOf(address _owner) public view returns (uint256 balance) {
        return balances[_owner];
    }
}

First, we need to get an instance for the challenge:

Integer Overflow on manbolq's Blog

Token - The Ethernaut - Writeup