Insufficient source of randomness

[c4-submissions]

Lines of code

https://github.com/code-423n4/2023-10-nextgen/blob/8b518196629faa37eae39736837b24926fd3c07c/smart-contracts/XRandoms.sol#L35-L43

Vulnerability details

Impact

    function randomNumber() public view returns (uint256){
        uint256 randomNum = uint(keccak256(abi.encodePacked(block.prevrandao, blockhash(block.number - 1), block.timestamp))) % 1000;
        return randomNum;
    }

    function randomWord() public view returns (string memory) {
        uint256 randomNum = uint(keccak256(abi.encodePacked(block.prevrandao, blockhash(block.number - 1), block.timestamp))) % 100;
        return getWord(randomNum);
    }

RandomizerNXT uses XRandoms, which in turn uses block.prevrandao, blockhash() and block.timestamp as a seed. These values are prone to manipulation and should not be used for deriving randomness.

Proof of Concept

Once an adversary is able to determine a rule by which the NFT traits depend on the random number, and because these 3 variables can always be retrieved without changing the state of the protocol, he may delay his transaction until the seed for randomness yields a satifactory value.

Recommended Mitigation Steps

Use only ChainlinkVRF or Arrng as sources of randomness.

Assessed type

Other

[c4-pre-sort]

141345 marked the issue as duplicate of #163

[c4-judge]

alex-ppg marked the issue as duplicate of #1901

[c4-judge]

alex-ppg marked the issue as unsatisfactory:
Invalid

[c4-judge]

alex-ppg marked the issue as unsatisfactory:
Invalid