AI Arena - bgsmallerbear's results

Lines of code

https://github.com/code-423n4/2024-02-ai-arena/blob/cd1a0e6d1b40168657d1aaee8223dc050e15f8cc/src/FighterFarm.sol#L379

Vulnerability details

Description

All users can predict the best reroll. As this can be compiled on remix for free with all predictable variables, a single user can create multiple wallets and freely check the best possible outcome for his fighter.

Impact

Users that (do this ) will be able to win more often because of the inceased weight, which will lead to bigger monetary gain.

Proof of Concept

1. User mints NFT
2. User checks which roll gives them the best value.
3. User calls this function

function testDna(uint256 rerolls, uint256 tokenId) public returns (uint256) {
    return uint256(keccak256(abi.encode(msg.sender, tokenId, rerolls))) %31 +65;
}

Example values: msg.sender = 0x5B38Da6a701c568545dCfcB03FcB875f56beddC4 rerolls = 1 tokenId= 0 => weight = 90

rerolls = 2 => weight 60 rerolls = 3 => 78

Recommended Mitigation Steps

Use chainlink VRF.

Assessed type

Other