Bvaults

title	description	type	network	date	loss_usd	returned_usd	tags	subcategory	vulnerable_contracts	tokens_lost	attacker_addresses	malicious_token	attack_block	reproduction_command	attack_txs	sources
BVaults	Manipulating token prices to drain protocol funds	Exploit	binance smart chain	2022-10-30	35000	0	business logic price manipulation		0xB2B1DC3204ee8899d6575F419e72B53E370F6B20	WBNB	0x5bfaa396c6fb7278024c6d7230b17d97ce8ab62d		22629432	forge test --match-contract Exploit_BVaults -vvv	0xe7b7c974e51d8bca3617f927f86bf907a25991fe654f457991cbf656b190fe94	title url Beosin Alert's Twitter https://twitter.com/BeosinAlert/status/1588579143830343683 title url Source Code https://bscscan.com/address/0xb2b1dc3204ee8899d6575f419e72b53e370f6b20#code

Step-by-step

1. Create a malicious token and pair
2. Inflate its price
3. Call convertDustToEarned
4. Swap again
5. Cashout and repeat

Detailed Description

This attack relies on the fack that BVault provided a convertDustToEarned method that would swap all of the tokens in the pool to "earned" tokens.

Unfortunately, it did not do any kind of price check or use any kind of smoothing of the price curve. This makes it vulnerable to price inflation: the attacker created a malicious token and pair, inflated the price of the token in the pool and then used it to gain earnedTokens.

    function convertDustToEarned() public whenNotPaused {
        require(isAutoComp, "!isAutoComp");

        // Converts dust tokens into earned tokens, which will be reinvested on the next earn().

        // Converts token0 dust (if any) to earned tokens
        uint256 _token0Amt = IERC20(token0Address).balanceOf(address(this));
        if (token0Address != earnedAddress && _token0Amt > 0) {
            _vswapSwapToken(token0Address, earnedAddress, _token0Amt);
        }

        // Converts token1 dust (if any) to earned tokens
        uint256 _token1Amt = IERC20(token1Address).balanceOf(address(this));
        if (token1Address != earnedAddress && _token1Amt > 0) {
            _vswapSwapToken(token1Address, earnedAddress, _token1Amt);
        }
    }

    function _vswapSwapToken(address _inputToken, address _outputToken, uint256 _amount) internal {
        IERC20(_inputToken).safeIncreaseAllowance(vswapRouterAddress, _amount);
        IValueLiquidRouter(vswapRouterAddress).swapExactTokensForTokens(_inputToken, _outputToken, _amount, 1, vswapPaths[_inputToken][_outputToken], address(this), now.add(1800));
    }

Possible mitigations

• Either introduce an oracle to get a second-source of truth for prices or use time-weighted-average to smooth the curve.

Related

• One Ring Finance - Share price manipulation via reserve balance changes
• Seaman - Forcing contracts to trade at manipulated token prices
• MBC Token - Price manipulation through public liquidity functions