DatingDapp
First Flight #33
Beginner FriendlyFoundrySolidityNFT
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Submission Details
Severity: low
Invalid

tokenURI Can Be Called on Non-Existent Tokens

0x68

tokenURI Can Be Called on Non-Existent Tokens

Description:

The tokenURI function attempts to check token ownership, but it does not properly handle non-existent tokens before calling ownerOf(tokenId).

Impact:

Calling tokenURI on an invalid tokenId may cause unexpected behavior or unnecessary computation.
A missing check could result in reverting transactions where they should return a clean error.

Proof of Concept:

​
function tokenURI(uint256 tokenId) public view virtual override returns (string memory) {
if (ownerOf(tokenId) == address(0)) { // <---- Problematic check
revert ERC721Metadata__URI_QueryFor_NonExistentToken();
}
​

ownerOf(tokenId) reverts if tokenId doesn't exist, which is inefficient.
The correct approach is to use _exists(tokenId), which is provided by OpenZeppelin’s ERC721 implementation.

Recommended Mitigation:

Change the tokenURI function to:

​
function tokenURI(uint256 tokenId) public view virtual override returns (string memory) {
require(_exists(tokenId), "ERC721Metadata: URI query for nonexistent token");
​
string memory profileName = _profiles[tokenId].name;
uint256 profileAge = _profiles[tokenId].age;
string memory imageURI = _profiles[tokenId].profileImage;
​
return string(
abi.encodePacked(
_baseURI(),
Base64.encode(
bytes(
abi.encodePacked(
'{"name":"',
profileName,
'", ',
'"description":"A soulbound dating profile NFT.", ',
'"attributes": [{"trait_type": "Age", "value": ',
Strings.toString(profileAge),
"}], ",
'"image":"',
imageURI,
'"}'
)
)
)
)
);
}
This change ensures that the tokenURI function checks for token existence before proceeding with the metadata retrieval.
---
Updates

Appeal created

n0kto Lead Judge 4 months ago
Submission Judgement Published
Invalidated
Reason: Non-acceptable severity
Assigned finding tags:

Informational or Gas

Please read the CodeHawks documentation to know which submissions are valid. If you disagree, provide a coded PoC and explain the real likelyhood and the detailed impact on the mainnet without any supposition (if, it could, etc) to prove your point.

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