Ethernaut - Walkthrough for Noobs - 7

This challenge will teach you, how to shove tokens down a contract's throat, even if the contract isn't necessarily accepting them.

The goal of this level is to make the balance of the contract greater than zero.

Background

Usually, a contract receives ether, in a payable function or the receive function, or the good ol' fallback function. But what if a contract has none of it?

There are three more unheard-of ways to do this:

selfdestruct(): We will talk about this more, in the challenge. This little thing has created a lot of security problem.
A contract can also receive Ether as a recipient of a miner block reward.
We can also deposit funds into an address before it is deployed, since we can pre-calculate the contract address before it is generated.

In this challenge, we would use selfdestruct() , this function removes a contract from blockchain. Note: This isn't equivalent to deleting stuff from your hard drive, your past transactions etc., will remain on the blockchain.

It looks like this:

selfdestruct(_address);

Whenever this function is called, the ether in the contract will be forcefully sent to the _address mentioned in the argument.

Code of Importance - or the Lack of it.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract Force {/*

                   MEOW ?
         /\_/\   /
    ____/ o o \
  /~____  =ø= /
 (______)__m_m)

*/}

This is an empty contract, without any functions, fallbacks, or constructors. I mean the cat is cute though, but doesn't really help.

The plan of action would be to create a contract, get some goerli, or sepolia in it, and self-destruct it to this address.

Solution

Open Remix.

  // SPDX-License-Identifier: MIT
  pragma solidity ^0.8.0;

  contract WillSelfDestruct {
      constructor() payable {
      }
      function shovesEther(address _EthernautContractAddress) public {
          selfdestruct(payable(_EthernautContractAddress));

      }
  }
  //code is self explanatory.

Compile and Deploy this with '1000000' Wei, or any value for that matter.
In the "Deployed Contract" section in the "Deploy and run" section, put your instance address as the _EthernautContractAddress
Run the shovesEther function.
Submit Instance.

Force✅

Ethernaut - Walkthrough for Noobs - 7 - Force

Table of contents

Background

Code of Importance - or the Lack of it.

Solution