Submission Details
Impact:
Likelihood:
MED-01: Unchecked Return Value of ERC721 _mint()
MED-01: Unchecked Return Value of ERC721 _mint()
Description
The _mint() function from ERC721 returns a uint256 token ID, but the return value is not checked. While OpenZeppelin's _mint() reverts on failure, explicitly checking the return value is a best practice for clarity and defense-in-depth.
// Root cause in the codebase with @> marks to highlight the relevant section
function selectWinner() external {
// ...
@> _mint(winner, tokenId);
// No check of return value
}
Risk
Likelihood:
Low - OpenZeppelin's _mint() reverts on failure
But silent failures possible if implementation changes
Impact:
Token ID tracking could be incorrect
tokenIdToRaritymapping might not match actual minted token
Proof of Concept
// If _mint() ever returned 0 or failed silently:
// tokenIdToRarity[tokenId] = rarity; // Would use wrong tokenId
// tokenId++; // Would increment incorrectly
Recommended Mitigation
function selectWinner() external {
// ...
- _mint(winner, tokenId);
+ uint256 mintedTokenId = _mint(winner, tokenId);
+ require(mintedTokenId == tokenId, "PuppyRaffle: Mint failed or returned unexpected tokenId");
tokenIdToRarity[tokenId] = rarity;
tokenId++;
}
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