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Submission Details
Severity: medium
Invalid

`LibOracle.sol::getOraclePrice` will return the wrong price for asset if underlying aggregator hits minAnswer

hunter_w3b

Summary

Chainlink aggregators have a built in circuit breaker if the price of an asset goes outside of a predetermined price band. The result is that if an asset experiences a huge drop in value (i.e. LUNA crash) the price of the oracle will continue to return the minPrice instead of the actual price of the asset. This would allow user to continue borrowing with the asset but at the wrong price. This is exactly what happened to Venus on BSC when LUNA imploded.

Vulnerability Details

LibOracle.sol::getOraclePrice uses the ChainlinkFeedRegistry to obtain the price of the requested tokens.

function getOraclePrice(address asset) internal view returns (uint256) {
AppStorage storage s = appStorage();
AggregatorV3Interface baseOracle = AggregatorV3Interface(s.baseOracle);
uint256 protocolPrice = getPrice(asset);
// prettier-ignore
(
uint80 baseRoundID,
int256 basePrice,
/*uint256 baseStartedAt*/
,
uint256 baseTimeStamp,
/*uint80 baseAnsweredInRound*/
) = baseOracle.latestRoundData();
​
AggregatorV3Interface oracle = AggregatorV3Interface(s.asset[asset].oracle);
if (address(oracle) == address(0)) revert Errors.InvalidAsset();
​
if (oracle == baseOracle) {
//@dev multiply base oracle by 10**10 to give it 18 decimals of precision
uint256 basePriceInEth = basePrice > 0
? uint256(basePrice * Constants.BASE_ORACLE_DECIMALS).inv()
: 0;
basePriceInEth = baseOracleCircuitBreaker(
protocolPrice, baseRoundID, basePrice, baseTimeStamp, basePriceInEth
);
return basePriceInEth;
} else {
// prettier-ignore
(
uint80 roundID,
int256 price,
/*uint256 startedAt*/
,
uint256 timeStamp,
/*uint80 answeredInRound*/
) = oracle.latestRoundData();
uint256 priceInEth = uint256(price).div(uint256(basePrice));
oracleCircuitBreaker(
roundID, baseRoundID, price, basePrice, timeStamp, baseTimeStamp
);
return priceInEth;
}
}

ChainlinkFeedRegistry#latestRoundData pulls the associated aggregator and requests round data from it. ChainlinkAggregators have minPrice and maxPrice circuit breakers built into them. This means that if the price of the asset drops below the minPrice, the protocol will continue to value the token at minPrice instead of it's actual value. This will allow users to take out huge amounts of bad debt and bankrupt the protocol.

Example: TokenA has a minPrice of $1 The price of TokenA drops to $0.10 The aggregator still returns $1 allowing the user to borrow against TokenA as if it is $1 which is 10x it's actual value.

Note: Chainlink oracles are used a just one piece of the OracleAggregator system and it is assumed that using a combination of other oracles, a scenario like this can be avoided. However this is not the case because the other oracles also have their flaws that can still allow this to be exploited. As an example if the chainlink oracle is being used with a UniswapV3Oracle which uses a long TWAP then this will be exploitable when the TWAP is near the minPrice on the way down. In a scenario like that it wouldn't matter what the third oracle was because it would be bypassed with the two matching oracles prices. If secondary oracles like Band are used a malicious user could DDOS relayers to prevent update pricing. Once the price becomes stale the chainlink oracle would be the only oracle left and it's price would be used.

Impact

In the event that an asset crashes (i.e. LUNA) the protocol can be manipulated to give out loans at an inflated price

Tools Used

Manual Review

Recommendations

​
(
uint80 baseRoundID,
int256 basePrice,
/*uint256 baseStartedAt*/
,
uint256 baseTimeStamp,
/*uint80 baseAnsweredInRound*/
) = baseOracle.latestRoundData();
​
+ if (basePrice >= maxPrice or basePrice <= minPrice) revert();
Updates

Lead Judging Commences

0xnevi Lead Judge
almost 2 years ago
0xnevi Lead Judge almost 2 years ago
Submission Judgement Published
Invalidated
Reason: Known issues

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