Summary
distributeAssets() calculates costInEuros by using:
uint256 costInEuros = _portion * 10 ** (18 - asset.token.dec) * uint256(assetPriceUsd) / uint256(priceEurUsd)
where assetPriceUsd and priceEurUsd are raw values fetched through chainlink latestRoundData() function. This assumes that all price feeds will have the same decimal precision (apparently, 8 is the general supposition made by the protocol), but this is not the case. For example AMPL / USD feed has 18 decimals.
Any mismatch between the decimals of EUR/USD price feed and ASSET/USD price feed could cause incorrect calculation of -
breaking major functionality across the protocol like -
LiquidationPool.sol#L205-L241
function distributeAssets(ILiquidationPoolManager.Asset[] memory _assets, uint256 _collateralRate, uint256 _hundredPC) external payable {
consolidatePendingStakes();
(,int256 priceEurUsd,,,) = Chainlink.AggregatorV3Interface(eurUsd).latestRoundData();
uint256 stakeTotal = getStakeTotal();
uint256 burnEuros;
uint256 nativePurchased;
for (uint256 j = 0; j < holders.length; j++) {
Position memory _position = positions[holders[j]];
uint256 _positionStake = stake(_position);
if (_positionStake > 0) {
for (uint256 i = 0; i < _assets.length; i++) {
ILiquidationPoolManager.Asset memory asset = _assets[i];
if (asset.amount > 0) {
(,int256 assetPriceUsd,,,) = Chainlink.AggregatorV3Interface(asset.token.clAddr).latestRoundData();
uint256 _portion = asset.amount * _positionStake / stakeTotal;
@--------------> uint256 costInEuros = _portion * 10 ** (18 - asset.token.dec) * uint256(assetPriceUsd) / uint256(priceEurUsd)
* _hundredPC / _collateralRate;
if (costInEuros > _position.EUROs) {
_portion = _portion * _position.EUROs / costInEuros;
costInEuros = _position.EUROs;
}
_position.EUROs -= costInEuros;
rewards[abi.encodePacked(_position.holder, asset.token.symbol)] += _portion;
@--------------> burnEuros += costInEuros;
if (asset.token.addr == address(0)) {
nativePurchased += _portion;
} else {
IERC20(asset.token.addr).safeTransferFrom(manager, address(this), _portion);
}
}
}
}
positions[holders[j]] = _position;
}
@---> if (burnEuros > 0) IEUROs(EUROs).burn(address(this), burnEuros);
returnUnpurchasedNative(_assets, nativePurchased);
}
Vulnerability Details
Let us consider an example:
-
1 EUR = 1.09621 USD. That is, Chainlink's priceEurUsd (8 decimal precision for this price feed)
-
Let's assume an asset TOX with 18 decimal places
-
1 TOX = 1.09621 USD. That is, Chainlink's assetPriceUsd (18 decimal precision for this price feed)
-
Let _portion be equal to
-
Incorrect calculation as per L220:
$$
\begin{equation}
\begin{split} costInEuros &= 10 * {10}^{18-18} * 1096210000000000000 \div 109621000 * 100000 \div 120000 \
&= 10 * {10}^0 * 10000000000 * 100000 \div 120000 \
&= 83333333333 \
\end{split}
\end{equation}
$$
-
Correct expected calculation (modified for simplicity, see the recommendation section below for exact changes to be made):
$$
\begin{equation}
\begin{split} costInEuros &= 10 * {10}^{18-18} * 109621000 \div 109621000 * 100000 \div 120000 \
&= 10 * {10}^0 * 1 * 100000 \div 120000 \
&= 8 \
\end{split}
\end{equation}
$$
-
The incorrect value of costInEuros = 83333333333 will cause _portion to be evaluated to a much lower value in L223 since 83333333333 is in the denominator here. Therefore, the rewards calculated on L227 is extremely low for the user. Also, _position.EUROs will be set to 0 on L226.
Impact
users getting lesser than expected rewards
users getting their EUROs burned unfairly
incorrect calculations across protocol
Tools Used
Manual inspection
Recommendations
Consider calling decimals() function on the price feed contract to get the correct decimals and calculate the value based on the returned decimals:
function distributeAssets(ILiquidationPoolManager.Asset[] memory _assets, uint256 _collateralRate, uint256 _hundredPC) external payable {
+ uint256 DECIMAL_PRECISION_SAVER = 30;
consolidatePendingStakes();
(,int256 priceEurUsd,,,) = Chainlink.AggregatorV3Interface(eurUsd).latestRoundData();
+ uint256 decimalsEurUsd = uint256(Chainlink.AggregatorV3Interface(eurUsd).decimals());
uint256 stakeTotal = getStakeTotal();
uint256 burnEuros;
uint256 nativePurchased;
for (uint256 j = 0; j < holders.length; j++) {
Position memory _position = positions[holders[j]];
uint256 _positionStake = stake(_position);
if (_positionStake > 0) {
for (uint256 i = 0; i < _assets.length; i++) {
ILiquidationPoolManager.Asset memory asset = _assets[i];
if (asset.amount > 0) {
(,int256 assetPriceUsd,,,) = Chainlink.AggregatorV3Interface(asset.token.clAddr).latestRoundData();
+ uint256 decimalsAssetUsd = uint256(Chainlink.AggregatorV3Interface(asset.token.clAddr).decimals());
uint256 _portion = asset.amount * _positionStake / stakeTotal;
- uint256 costInEuros = _portion * 10 ** (18 - asset.token.dec) * uint256(assetPriceUsd) / uint256(priceEurUsd)
- * _hundredPC / _collateralRate;
+ uint256 costInEuros = _portion * 10 ** (18 - asset.token.dec) * _hundredPC * uint256(assetPriceUsd) * (10 ** (DECIMAL_PRECISION_SAVER - decimalsAssetUsd)) / (uint256(priceEurUsd) * (10 ** (DECIMAL_PRECISION_SAVER - decimalsEurUsd)) * _collateralRate);
if (costInEuros > _position.EUROs) {
_portion = _portion * _position.EUROs / costInEuros;
costInEuros = _position.EUROs;
}
_position.EUROs -= costInEuros;
rewards[abi.encodePacked(_position.holder, asset.token.symbol)] += _portion;
burnEuros += costInEuros;
if (asset.token.addr == address(0)) {
nativePurchased += _portion;
} else {
IERC20(asset.token.addr).safeTransferFrom(manager, address(this), _portion);
}
}
}
}
positions[holders[j]] = _position;
}
if (burnEuros > 0) IEUROs(EUROs).burn(address(this), burnEuros);
returnUnpurchasedNative(_assets, nativePurchased);
}
