Alchemix Transmuter

Summary

https://github.com/Cyfrin/2024-12-alchemix/blob/82798f4891e41959eef866bd1d4cb44fc1e26439/src/StrategyArb.sol#L84

Vulnerability Details

According to the annotation, you want to ensure that the exchange occurs at a premium, meaning that the amount of alETH obtained through the swap is greater than the amount of WETH input. This implies that minOut should be greater than _amount, ensuring that the swap yields at least an equal or greater amount of alETH than the input.

In practice, the minOut parameter of the swapExactTokensForTokens function is typically used to prevent slippage caused by price fluctuations, ensuring that the swap yields at least a reasonable minimum amount. However, strictly requiring minOut > _amount may result in most transactions failing unless the value of alETH is indeed consistently higher than WETH. Such a restriction is overly stringent and may not align with real market conditions, especially in highly volatile environments.

If minOut is set too high and the market cannot meet this requirement, the transaction will consistently fail, rendering the functionality unusable.

The annotation mentions the need to check whether the price is better than 1:1, but the actual code does not implement price validation based on an oracle. Instead, it simply compares minOut and _amount for a basic determination. This approach lacks flexibility and is prone to being affected by market fluctuations.

Impact

Tools Used

Recommendations

Using an on-chain oracle (such as Chainlink) to fetch the current prices of WETH and alETH allows for the dynamic calculation of minOut, ensuring the rationality of the swap. By leveraging real-time pricing data, this approach can adapt to market conditions and provide a more accurate and flexible safeguard against slippage or unfavorable rates.