## Description `ThunderLoan::updateFlashLoanFee()` and `ThunderLoanUpgraded::updateFlashLoanFee()` does not emit an event, so it is difficult to track changes in the value `s_flashLoanFee` off-chain. ## Vulnerability Details ```solidity function updateFlashLoanFee(uint256 newFee) external onlyOwner { if (newFee > FEE_PRECISION) { revert ThunderLoan__BadNewFee(); } @> s_flashLoanFee = newFee; } ``` ## Impact In Ethereum, events are used to facilitate communication between smart contracts and their user interfaces or other off-chain services. When an event is emitted, it gets logged in the transaction receipt, and these logs can be monitored and reacted to by off-chain services or user interfaces. Without a `FeeUpdated` event, any off-chain service or user interface that needs to know the current `s_flashLoanFee` would have to actively query the contract state to get the current value. This is less efficient than simply listening for the `FeeUpdated` event, and it can lead to delays in detecting changes to the `s_flashLoanFee`. The impact of this could be significant because the `s_flashLoanFee` is used to calculate the cost of the flash loan. If the fee changes and an off-chain service or user is not aware of the change because they didn't query the contract state at the right time, they could end up paying a different fee than they expected. ## Recommendations Emit an event for critical parameter changes. ```diff + event FeeUpdated(uint256 indexed newFee); function updateFlashLoanFee(uint256 newFee) external onlyOwner { if (newFee > s_feePrecision) { revert ThunderLoan__BadNewFee(); } s_flashLoanFee = newFee; + emit FeeUpdated(s_flashLoanFee); } ```