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code-423n4 / 2021-09-yaxis-findings

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_harvest and _swap #159

Closed code423n4 closed 2 years ago

code423n4 commented 2 years ago

Handle

tensors

Vulnerability details

Impact

The minimum amount out on the implemented _harvest and _swap methods means that attackers can manipulate the price with flashloans/frontrun before calling _harvest to actually force the output to be small, pocketing the difference for themselves when they swap back.

Proof of Concept

https://github.com/code-423n4/2021-09-yaxis/blob/cf7d9448e70b5c1163a1773adb4709d9d6ad6c99/contracts/v3/strategies/NativeStrategyCurve3Crv.sol#L108-L127

Only 1 wei is expected output from the _harvest and the _swap call inside it on line 120.

Recommended Mitigation Steps

The expected amount out should be carefully deduced. A common solution is to use a chainlink oracle.

BobbyYaxis commented 2 years ago

Harvest can't be called by non-whitelisted addresses

GalloDaSballo commented 2 years ago

The fact that only a whitelisted address can call the harvest doesn't mitigate against frontrunning

Anyone can see the function in the mempool and frontrun it or sandwich the swaps

Recommend mitigating via flashbots / private transactions or by rolling an additional set of checks for slippage

Duplicate of #140