Submission Details
Severity:
ERC20 return values not checked
Summary
The ERC20.transfer() and ERC20.transferFrom() functions return a boolean value indicating success. This parameter needs to be checked for success. Some tokens do not revert if the transfer failed but return false instead.
_battle() function does not check the return value of these functions.
Vulnerability Details
function _battle(uint256 _tokenId, uint256 _credBet) internal {
address _defender = defender;
require(defenderBet == _credBet, "RapBattle: Bet amounts do not match");
uint256 defenderRapperSkill = getRapperSkill(defenderTokenId);
uint256 challengerRapperSkill = getRapperSkill(_tokenId);
uint256 totalBattleSkill = defenderRapperSkill + challengerRapperSkill;
uint256 totalPrize = defenderBet + _credBet;
uint256 random =
uint256(keccak256(abi.encodePacked(block.timestamp, block.prevrandao, msg.sender))) % totalBattleSkill;
// Reset the defender
defender = address(0);
emit Battle(msg.sender, _tokenId, random < defenderRapperSkill ? _defender : msg.sender);
// If random <= defenderRapperSkill -> defenderRapperSkill wins, otherwise they lose
if (random <= defenderRapperSkill) {
// We give them the money the defender deposited, and the challenger's bet
@> credToken.transfer(_defender, defenderBet);
@> credToken.transferFrom(msg.sender, _defender, _credBet);
} else {
// Otherwise, since the challenger never sent us the money, we just give the money in the contract
credToken.transfer(msg.sender, _credBet);
}
totalPrize = 0;
// Return the defender's NFT
oneShotNft.transferFrom(address(this), _defender, defenderTokenId);
}
Impact
Tokens that don't actually perform the transfer and return false are still counted as a correct transfer.
Tools Used
Manual Review
Recommendations
We recommend using OpenZeppelin’s SafeERC20 versions with the safeTransfer() and safeTransferFrom() functions that handle the return values check.
Rewards breakdown
nSLOC
201This contest has a flat reward structure with the following payouts:
100 EXP
20 EXP
2 EXP
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