Ethernaut, #2 Fallback

Sat, 23 Jul 2022 00:00:00 +0000

To complete this level we need become the owner of the contract and reduce its balance to zero.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.2;

contract Fallback {
    mapping(address => uint256) public contributions;
    address payable public owner;

    constructor() {
        owner = payable(msg.sender);
        contributions[msg.sender] = 1000 * (1 ether);
    }

    modifier onlyOwner() {
        require(msg.sender == owner, "caller is not the owner");
        _;
    }

    function contribute() public payable {
        require(msg.value < 0.001 ether, "msg.value must be < 0.001");
        contributions[msg.sender] += msg.value;
        if (contributions[msg.sender] > contributions[owner]) {
            owner = payable(msg.sender);
        }
    }

    function getContribution() public view returns (uint256) {
        return contributions[msg.sender];
    }

    function withdraw() public onlyOwner {
        owner.transfer(address(this).balance);
    }

    receive() external payable {
        require(msg.value > 0 && contributions[msg.sender] > 0);
        owner = payable(msg.sender);
    }
}

I’ve modified the original level code and removed the SafeMath usage since we’re using solidity ^0.8.2.

Ethernaut, #1 Hello Ethernaut

Thu, 21 Jul 2022 00:00:00 +0000

Intro Link to heading

The Ethernaut CTF game exists for more than 3 years already and has 26 challenges. The first one is a kind of introductory challenge that gives you steps on what you need to set up. If you have Metamask and open the browser’s console, you should see greeting messages:

Set up Link to heading

Originally, this game runs on the Rinkeby test network, but we’re going to play it locally. As I mentioned in the first post, we will use Foundry toolchain and here is the initial/empty project layout:

Ethernaut on transcendental kyberautism

Ethernaut, #2 Fallback

Ethernaut, #1 Hello Ethernaut

Intro Link to heading

Set up Link to heading