How did this happen?
Details of vulnerability
1. Calculation of exchange rates
location: ResupplyPaircore.sol: 573
_exchangeRate = 1e36 / IOracle(_exchangeRateInfo.oracle).getPrices(address(collateral));problem: If the prices of Oracle are very large due to the integer department without rounding protection, the exchange rate drops to zero.
2. ERC4626 Donation Attack Vector
location: ResupplyPaircore.sol: 155-156
underlying = IERC20(IERC4626(_collateral).asset());-The attacker can donate assets directly to the safe.
-This is a significant expansion of the price per share
-Oracle accurately reports the expansion price
-Crelmented exchange rate calculation: `1E36 / exth_large_number = 0`
3. Test of broken payment ability
location: ResupplyPaircore.sol: 282
uint256 _ltv = ((_borrowerAmount * _exchangeRate * LTV_PRECISION) / EXCHANGE_PRECISION) / _collateralAmount;
return _ltv <= _maxLTV;when _EXCHANGERATE = 0
-LTV calculation:
(_borrowerAmount * 0 * LTV_PRECISION) / EXCHANGE_PRECISION / _collateralAmount = 0– check: 0 <= _maxltv always Returns the truth
result: All collateral allows unlimited borrowing
Attack scenario
target: cvcrvusd ERC4626 safe (almost empty when distributed)
1. Initial operation:
The attacker made a big donation to artificially expand the ‘Pricepershare’ after depositing one WEI in the empty CVCRVUSD safe.
2. Exchange rate:
Attacker:
-An called borrow() Newly deployed ResupplyPair
-Triggered Oracle Price Fetch: GetPrices (address (collateral))
-The price is very high due to donation inflation
3. Solvency bypass:
– _issolvent () Inspired inspection used _EXCHANGERATE = 0
-LTV calculation:
(_borrowAmount * 0 * LTV_PRECISION) / EXCHANGE_PRECISION / _collateralAmount = 0– check 0 <= _maxltv Always return the truth
4. Bulk:
The attacker used only one WEI collateral to borrow $ 10 million in reuse to exchange and redistribute the stolen funds. This led to A Final profit 9.56 million It is divided into several addresses.
General attack pattern
1. Target new or low liquid ERC4626 vault.
2. Donate a large amount of basic assets to expand the stock price.
3. Sharing mint minimum safe (1 Wei)
4. Oracle prices expand to astronomical levels
5. The exchange rate due to the integer department drops to zero.
6. Minimal collateral and bypass LTV inspection
7. Borrow the maximum available funds
Recommendation
Immediate relief
1. Add the exchange rate floor
_exchangeRate = 1e36 / IOracle(_exchangeRateInfo.oracle).getPrices(address(collateral));
require(_exchangeRate > 0, "Invalid exchange rate");
_exchangeRate = _exchangeRate == 0 ? 1 : _exchangeRate;2. Add the minimum mortgage requirements
Enforce the minimum deposit for ERC4626 and implement a share/asset ratio.
reference
-ERC4626 Standard: https://eips.ethereum.org/eips/eip-4626
-RESUPPLYFI official response: https://x.com/resupplyfi/status/193809252431036491
-Standum safe: CVCRVUSD ERC4626 Vault
