Incorrect ERC721 interfaces SLITHER-W1033

Incorrect return values for ERC721 functions. A contract compiled with solidity > 0.4.22 interacting with these functions will fail to execute them, as the return value is missing.

Exploit Scenario

contract Token{
    function ownerOf(uint256 _tokenId) external view returns (bool);
    //...
}

Token.ownerOf does not return an address like ERC721 expects. Bob deploys the token. Alice creates a contract that interacts with it but assumes a correct ERC721 interface implementation. Alice's contract is unable to interact with Bob's contract.

Recommendation

Set the appropriate return values and vtypes for the defined ERC721 functions.

Learn more

erc721-interface on Slither's wiki.