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medium Token Standards No SWC entry CWE-393

NFT Receiver / onERC721Received Missing Validation

SAFE-0091 Token Standards Checked automatically by the scanner
1

What goes wrong

A contract meant to custody NFTs does not implement IERC721Receiver, so safeTransferFrom into it reverts (locking flows) or, if it implements it incautiously, opens a reentrancy/acceptance hole.

2

How to fix it

the pattern that is safe
function onERC721Received(address,address,uint256,bytes calldata)
    external pure returns (bytes4){ return IERC721Receiver.onERC721Received.selector; }
◆
Implement and validate the receiver hook.
3

Related vulnerabilities in Token Standards

SAFE-0053Unsafe / Unprotected Minting critical · Token Standards SAFE-0051Missing SafeERC20 / Non-Standard Token Handling high · Token Standards SAFE-0052Fee-on-Transfer / Rebasing Token Accounting Mismatch high · Token Standards SAFE-0055Burn Authorization / Burn-From Missing Checks high · Token Standards SAFE-0107Fee-on-Transfer / Rebasing Token Mis-Accounting high · Token Standards SAFE-0208Non-Standard ERC20 Return Value Not Handled high · Token Standards SAFE-0050ERC-20 Approval Race Condition medium · Token Standards SAFE-0054ERC-721/1155 Missing Receiver Validation (Safe Transfer) medium · Token Standards
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