balanceAtEpochOf will revert

[code423n4]

Lines of code

https://github.com/code-423n4/2022-05-vetoken/blob/2d7cd1f6780a9bcc8387dea8fecfbd758462c152/contracts/VE3DLocker.sol#L305-L315

Vulnerability details

Impact

The line for (uint256 i = locks.length - 1; i + 1 != 0; i--) { relies on uint256 underflow and overflow, which would revert in solidity ^0.8.0

Proof of Concept

https://github.com/code-423n4/2022-05-vetoken/blob/2d7cd1f6780a9bcc8387dea8fecfbd758462c152/contracts/VE3DLocker.sol#L305-L315

    function balanceAtEpochOf(uint256 _epoch, address _user) public view returns (uint256 amount) {
        LockedBalance[] storage locks = userLocks[_user];

        //get timestamp of given epoch index
        uint256 epochTime = epochs[_epoch].date;
        //get timestamp of first non-inclusive epoch
        uint256 cutoffEpoch = epochTime.sub(lockDuration);

        //need to add up since the range could be in the middle somewhere
        //traverse inversely to make more current queries more gas efficient
        for (uint256 i = locks.length - 1; i + 1 != 0; i--) {

[jetbrain10]

same as #150

[GalloDaSballo]

Dup of #150