Improper Validation Of Chainlink's latestAnswer Function

[code423n4]

Handle

leastwood

Vulnerability details

Impact

The latestAnswer function does not allow EIP1271Wallet._validateOrder to validate the output of the Chainlink oracle query. As a result, it is possible for off-chain orders to use stale results, potentially allowing the taker of the order to extract more value from the treasury. latestRoundData is able to ensure the round is complete and has returned a valid/expected price by validating additional round data. This is documented here.

Proof of Concept

https://github.com/code-423n4/2022-01-notional/blob/main/contracts/utils/EIP1271Wallet.sol#L175-L177

uint256 oraclePrice = _toUint(
    AggregatorV2V3Interface(priceOracle).latestAnswer()
);

Tools Used

Manual code review.
Chainlink best practices.

Recommended Mitigation Steps

Consider using Chainlink's latestRoundData function instead of latestAnswer to validate the output correctly. This can be updated to match the following code snippet:

(
  uint80 roundID,
  int256 oraclePrice,
  ,
  uint256 updateTime,
  uint80 answeredInRound
) = AggregatorV2V3Interface(priceOracle).latestRoundData();
require(
  answeredInRound >= roundID,
  "Notional: Chainlink Price Stale"
);
require(oraclePrice > 0, "Notional: Chainlink Malfunction");
require(updateTime != 0, "Notional: Incomplete round");

[jeffywu]

Duplicate #178

[pauliax]

A duplicate of #197