Oracle price data
Oracles are a common choice to receive price data for assets. The price data from oracles can be harder to manipulate than price data from a DeFi protocol's swap pool, but there are common oracle integration issues that should be kept in mind.
Other resources:
1. Is the spot price of a pool used?
Incorrect
Yes, spot price is used and it can be manipulated by flashloans
Correct
A decentralized oracle (Chainlink, Band, UMA, etc.), Uniswap v3 TWAP or similar
Explanation
Flashloan price manipulation has caused many protocol hacks, making price manipulation hacks one of the most common attack vectors
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2. Are variable decimals for different token pair price feeds accounted for?
Incorrect
No, a constant decimals value is hardcoded
Correct
Yes
Explanation
Incorrect decimals can lead to accounting errors
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3. If Uniswap v3 TWAP is used for price data, is post-merge PoS manipulation accounted for?
Incorrect
No, TWAP is fully trusted
Correct
Yes
Explanation
Incorrect decimals can lead to accounting errors
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Chainlink Oracle
1. Is a deprecated Chainlink function used, such as latestAnswer(), latestRound(), or getTimestamp()?
Incorrect
Yes
Correct
No
Explanation
Deprecated functions may not be supported in the future, which could cause a denial of service
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2. Is there proper validation of latestRoundData()?
Incorrect
No
Correct
Yes, price is confirmed to be in the range of minAnswer and maxAnswer limits, the timestamp of the latest answer is checked against zero and a stale feed threshold that depends on the update frequency of the oracle for each specific token
Explanation
Insufficient validation of oracle can lead to the acceptance of bad data
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3. Is the price query in a try/catch?
Incorrect
No
Correct
Yes, latestRoundData call is in a try/catch block
Explanation
Access to price feed data may be removed due to the multisig ownership of Chainlink's EACAggregatorProxy contract which is queried for price data. If uptime is a key part of a protocol's design and the Chainlink multisig is not considered a trusted entity, a backup mode of operation should exist in the catch block of the try/catch price query to handle the edge case where the primary Chainlink price feed is not available.
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