Weak PRNG found in randomPool.randomNumber()

[c4-submissions]

Lines of code

https://github.com/code-423n4/2023-10-nextgen/blob/8b518196629faa37eae39736837b24926fd3c07c/smart-contracts/XRandoms.sol#L36

Vulnerability details

Impact

If the PRNG is weak, the sequence of generated random numbers may be predictable or easy to guess by the attacker. This predictability can be exploited by attackers to gain an unfair advantage or manipulate the contract's behavior.

In situations where randomness is used to determine outcomes, especially in decentralized finance (DeFi) applications, a weak PRNG can lead to front-running attacks. Malicious actors could anticipate random number generation and act strategically to exploit the system.

In financial applications, a weak PRNG can lead to a loss of funds if attackers can predict outcomes or manipulate random choices in their favor.

Proof of Concept

randomPool.randomNumber() (smart-contracts/XRandoms.sol#35-38) uses a weak PRNG: "randomNum = uint256(keccak256(bytes)(abi.encodePacked(block.prevrandao,blockhash(uint256)(block.number - 1),block.timestamp))) % 1000 (smart-contracts/XRandoms.sol#36)"

Tools Used

Manual code review

Recommended Mitigation Steps

Weak PRNG due to a modulo on block.timestamp, now or blockhash. These can be influenced by miners to some extent so they should be avoided. Do not use block.timestamp, now or blockhash as a source of randomness.

Consider using cryptographic libraries that provide strong randomness guarantees. In Ethereum-based smart contracts, try using external services like Chainlink VRF, which provides a decentralized and verifiable source 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