Bad source of randomness

[c4-submissions]

Lines of code

https://github.com/code-423n4/2023-10-nextgen/blob/2467db02cc446374ab9154dde98f7e931d71584d/smart-contracts/XRandoms.sol#L41

Vulnerability details

Impact

Using block.number and block.timestamp as a source of randomness is commonly advised against, as the outcome can be manipulated by calling contracts. In this case,minter can get the word he like

Proof of Concept

This code get random by block.number and block.timestamp

    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);
    }

Malicious user is able to predict result and get the word nft he want

Tools Used

manual

Recommended Mitigation Steps

Consider using a decentralized oracle for the generation of random numbers, such as Chainlinks VRF.

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