# 31460 - \[SC - Insight] supportsInterface does not return typeIERCRecei... Submitted on May 19th 2024 at 21:40:50 UTC by @OxRizwan for [Boost | Alchemix](https://immunefi.com/bounty/alchemix-boost/) Report ID: #31460 Report type: Smart Contract Report severity: Insight Target: Impacts: * Contract fails to deliver promised returns, but doesn't lose value ## Description ## Brief/Intro `supportsInterface()` does not return `type(IERC721Receiver).interfaceId` ## Vulnerability Details `AlchemixGovernor.sol` contract has inherited `L2Governor` abstract as base contract. This base contract has `supportsInterface()` function which returns the supported interface id by Alchemix Governor contract. It should be noted that Alchemix governor contract supports both `IERC721Receiver` interface id and `IERC1155Receiver` interface id, however, the implementation of `supportsInterface` has only returned `IERC1155Receiver` and does not return the `IERC721Receiver` interface id and this can be seen as below: ```solidity function supportsInterface(bytes4 interfaceId) public view virtual override(IERC165, ERC165) returns (bool) { // In addition to the current interfaceId, also support previous version of the interfaceId that did not // include the castVoteWithReasonAndParams() function as standard return interfaceId == (type(IGovernor).interfaceId ^ this.castVoteWithReasonAndParams.selector ^ this.castVoteWithReasonAndParamsBySig.selector ^ this.getVotesWithParams.selector) || interfaceId == type(IGovernor).interfaceId || interfaceId == type(IERC1155Receiver).interfaceId || super.supportsInterface(interfaceId); } ``` ## Impact Details `supportsInterface()` does not explicitely return the `interfaceId == type(IERC721Receiver).interfaceId` while calling it. The Alchemix governor supports the ERC721Receiver but the interface id does not return it so its a low severity issue ## References ## Recommendation to fix ```diff function supportsInterface(bytes4 interfaceId) public view virtual override(IERC165, ERC165) returns (bool) { // In addition to the current interfaceId, also support previous version of the interfaceId that did not // include the castVoteWithReasonAndParams() function as standard return interfaceId == (type(IGovernor).interfaceId ^ this.castVoteWithReasonAndParams.selector ^ this.castVoteWithReasonAndParamsBySig.selector ^ this.getVotesWithParams.selector) || interfaceId == type(IGovernor).interfaceId || + interfaceId == type(IERC721Receiver).interfaceId || interfaceId == type(IERC1155Receiver).interfaceId || super.supportsInterface(interfaceId); } ``` ## Proof of Concept The issue is simple to understand and very straight forward. It explains the interfaceId function unable to return the promised return i.e `interfaceId == type(IERC721Receiver).interfaceId` as true. The issue is not complex so i believe it can be easily understood with above description and recommendation. Thank you for your understanding. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://reports.immunefi.com/alchemix/31460-sc-insight-supportsinterface-does-not-return-typeiercrecei....md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.