Challenge 12

tx.origin Misuse

MediumWithdrawal logic

Challenge

Review the withdrawal flow, its balance checks, and the order in which funds and accounting state are updated.

Starter code

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

contract FallbackIssue {
  mapping(address => uint) public balances;

  function deposit() public payable {
    balances[msg.sender] += msg.value;
  }

  function withdraw(uint amount) public {
    require(balances[msg.sender] >= amount, "Insufficient balance");
    // Review the transfer and balance-update order.
  }
}

Show hint

Validate the balance and update accounting safely around external calls.