0x73696d616f - Missing `updatedAt` and recommended timeout checks in `Kept.sol` fetched chainlink prices

[sherlock-admin2]

0x73696d616f

medium

Missing updatedAt and recommended timeout checks in Kept.sol fetched chainlink prices

Summary

PythOracle incentivizes the keeper with an amount pro-rata to the ether price, fetched from a Chainlink oracle. When using chainlink prices, it's important to check that the updatedAt return value from the latestRoundData() call is different than 0. Additionaly, a timeout should be added after which the updatedAt value is no longer valid (not fresh enough).

Vulnerability Detail

Here is a great article from 0xmacro explaining in detail these 2 important measures. The updatedAt value should be different than 0 and smaller than the current timestamp by only a hardcode timeout.

Impact

The keeper is incorrectly incentivized and could incur in losses. Would place the system in a DoS state as no one would want to incur losses to update the oracle prices (or losses to the protocol team).

Code Snippet

In Kept.sol, notice the keep() modifier and _etherPrice() functions. There are no checks in the Chainlink answer (besides it being negative, as it would underflow when converted to UFixed18).

modifier keep(UFixed18 multiplier, uint256 buffer, bytes memory data) {
    uint256 startGas = gasleft();

    _;

    uint256 gasUsed = startGas - gasleft();
    UFixed18 keeperFee = UFixed18Lib.from(gasUsed)
        .mul(multiplier)
        .add(UFixed18Lib.from(buffer))
        .mul(_etherPrice())
        .mul(UFixed18.wrap(block.basefee));

    _raiseKeeperFee(keeperFee, data);

    keeperToken().push(msg.sender, keeperFee);

    emit KeeperCall(msg.sender, gasUsed, multiplier, buffer, keeperFee);
}

/// @notice Returns the price of ETH in terms of the keeper token
/// @return The price of ETH in terms of the keeper token
function _etherPrice() private view returns (UFixed18) {
    (, int256 answer, , ,) = ethTokenOracleFeed().latestRoundData();
    return UFixed18Lib.from(Fixed18Lib.ratio(answer, 1e8)); // chainlink eth-usd feed uses 8 decimals
}

Tool used

Vscode, Hardhat, Manual Review

Recommendation

Add the following checks to _etherPrice():

function _etherPrice() private view returns (UFixed18) { // TO SUBMIT missing validation
    (, int256 answer, , uint256 updatedAt,) = ethTokenOracleFeed().latestRoundData();
    if (updatedAt == 0) revert OracleNotUpdatedError(); // sanity check
    if (block.timestamp - updatedAt > TIMEOUT) revert OracleStalePriceError(); // price staleness check
    return UFixed18Lib.from(Fixed18Lib.ratio(answer, 1e8)); // chainlink eth-usd feed uses 8 decimals
}

[sherlock-admin]

2 comment(s) were left on this issue during the judging contest.

141345 commented:

m

n33k commented:

unhandled stale price returned from latestRoundData()

[arjun-io]

In the event that the price is stale, we should still use the price as it is he best approximation of what the incentive reward should be. If we instead revert (as per the recommendation) then the entire system will be fully blocked, even disallowing keepers who are willing to take a loss to keep the system running.