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code-423n4 / 2022-01-yield-findings

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Cvx3CrvOracle returns 0 for small baseAmount #93

Open code423n4 opened 2 years ago

code423n4 commented 2 years ago

Handle

kenzo

Vulnerability details

Due to the precision of Chainlink oracle and Curve's virtual price, Cvx3CrvOracle will return 0 for very small baseAmount.

Impact

As it only happens with very small amounts, the impact is not big as far as I can tell. However one can imagine for example a scenario where a user will request to buy a small amount of Cvx3Crv, and a contract would use peek to know how much to charge. Since peek returns 0, the user wouldn't be charged anything and still be able to receive a small amount of Cvx3Crv.

Proof of Concept

For example, for real (taken from contracts) values of:

minStable = 388135165257710
virtualPrice = 1020217504409323943
baseAmount = 1000

The oracle will return 0.

Recommended Mitigation Steps

Consider reverting the transaction if baseAmount > 0 and quoteAmount == 0.

alcueca commented 2 years ago

That's true, and an issue that no one else saw in any of the previous audits, given that this was first done in the ChainlinkMultiOracle.

While I think there might be little risk about it, we'll think more deeply about it, and I personally appreciate you seeing this.

GalloDaSballo commented 2 years ago

I believe the finding to be valid, given the limited scope am conflicted on giving medium severity.

In the example given by the warden uint256 price = (threecrv.get_virtual_price() * minStable) / 1e18; 

3.9598229e32 // 32 zeroes
/
1e18

Gives us: 3.9598229e14

So for this condition quoteAmount = (baseAmount * price) / 1e18; Any baseAmount with less than 4 units will return a 0.

Hence we quantified the attack.

This is denominated in eth as well.

A gwei is 1e9

Because of EIP1559 there is no way to have a zero gas tx, I believe 1 gwei may be the minimum cost (but may be wrong)

This ultimately means that while the rounding is present there should be no economic incentive in exploiting it, as the MEV extractable has 4 order of magnitude but the minimum cost would have 9 (1 gwei = 10^9 wei)

At this time, given these considerations I believe the finding to be valid and to be of low severity