veRWA - hassan-truscova's results

Lines of code

https://github.com/code-423n4/2023-08-verwa/blob/main/src/VotingEscrow.sol#L572-L596 https://github.com/code-423n4/2023-08-verwa/blob/main/src/VotingEscrow.sol#L576 https://github.com/code-423n4/2023-08-verwa/blob/main/src/VotingEscrow.sol#L431-L446 https://github.com/code-423n4/2023-08-verwa/blob/main/src/VotingEscrow.sol#L439 https://github.com/code-423n4/2023-08-verwa/blob/main/src/VotingEscrow.sol#L487-L527 https://github.com/code-423n4/2023-08-verwa/blob/main/src/VotingEscrow.sol#L491 https://github.com/code-423n4/2023-08-verwa/blob/main/src/VotingEscrow.sol#L451-L466 https://github.com/code-423n4/2023-08-verwa/blob/main/src/VotingEscrow.sol#L459

Vulnerability details

Impact

VotingEscrow’s balanceOfAt and totalSupplyAt call _findUserBlockEpoch and _findBlockEpoc, respectively, to return their corresponding values for a given block. Because the balance and supply can vary within the same block, these functions can return different values when called on the current block.

VotingEscrow’s balanceOfAt(addr, block) and totalSupplyAt(block) use a binary search to return their values associated with the block:

function _findBlockEpoch(uint256 _block, uint256 _maxEpoch) internal view returns (uint256) {
 ....
 if (min >= max) break;
        uint256 mid = (min + max + 1) / 2;
        if (pointHistory[mid].blk <= _block) {
            min = mid;
        } else {
            max = mid - 1;
        }
   ....
}


function _findUserBlockEpoch(address _addr, uint256 _block) internal view returns (uint256) {
   ....
        if (min >= max) {
            break;
        }
        uint256 mid = (min + max + 1) / 2;
        if (userPointHistory[_addr][mid].blk <= _block) {
            min = mid;
        } else {
            max = mid - 1;
        }
    ....
}

If a block is contained in pointHistory, the latest one will be used. Points on the current block can be added indefinitely in pointHistory. As a result, a user calling balanceOfAt or totalSupplyAt on the current block might not receive the latest value.

Proof of Concept

Bob creates a voting contract that relies on balanceOfAt and totalSupplyAt. Eve creates a vote using block.number as a snapshot and corrupts the quorum percentage.

Tools Used

Manual + in-house tool

Recommended Mitigation Steps

document that balanceOfAt and totalSupplyAt must not be called on the current block.

Assessed type

Invalid Validation