MetaMask Delegation Framework

1 Executive Summary

This report presents the results of our engagement with MetaMask to review MetaMask Delegation Framework.

The review was conducted over two weeks, from October 21, 2024 to October 25, 2024, by Rai Yang and Sergii Kravchenko. A total of 5 person-days were spent.

The review is performed on the changes in the codebase that were made since the previous audit. The main changes are:

• Adding four new enforcer contracts.
• Switching the cryptography lib from Fresh Crypto Lib (FCL) to SmoothCryptoLib (SCL).
• Adding beforeAllHook/afterAllHook functions to ICaveatEnforcer.
• Changing order of afterHook executions.
• Using EIP712 standard in the DeleGatorCore.

2 Scope

Our review focused on the commit hash ec0c0d64a4fc1ccca24d5e910d5712e62d84c4b7. The list of files in scope can be found in the Appendix.

2.1 Objectives

Together with the MetaMask team, we identified the following priorities for our review:

1. Correctness of the implementation, consistent with the intended functionality and without unintended edge cases.
2. Identify known vulnerabilities particular to smart contract systems, as outlined in our Smart Contract Best Practices, and the Smart Contract Weakness Classification Registry.

3 Findings

Each issue has an assigned severity:

• Minor issues are subjective in nature. They are typically suggestions around best practices or readability. Code maintainers should use their own judgment as to whether to address such issues.
• Medium issues are objective in nature but are not security vulnerabilities. These should be addressed unless there is a clear reason not to.
• Major issues are security vulnerabilities that may not be directly exploitable or may require certain conditions in order to be exploited. All major issues should be addressed.
• Critical issues are directly exploitable security vulnerabilities that need to be fixed.

{
    (address token_, address recipient_,) = getTermsInfo(_terms);
    bytes32 hashKey_ = _getHashKey(msg.sender, token_, recipient_, _delegationHash);
    require(!isLocked[hashKey_], "ERC721BalanceGteEnforcer:enforcer-is-locked");
    isLocked[hashKey_] = true;
    uint256 balance_ = IERC721(token_).balanceOf(recipient_);
    balanceCache[hashKey_] = balance_;
}

bytes4 selector_ = bytes4(callData_[0:4]);

// Decode the remaining callData into NFT transfer parameters
// The calldata should be at least 100 bytes (4 bytes for the selector + 96 bytes for the parameters)
if (callData_.length < 100) {
    revert("ERC721TransferEnforcer:invalid-calldata-length");
}

bytes4 selector = bytes4(callData_[0:4]);
require(selector == IERC173.transferOwnership.selector, "OwnershipTransferEnforcer:invalid-method");

require(callData_.length == 36, "OwnershipTransferEnforcer:invalid-execution-length");

Appendix 1 - Files in Scope

This audit covered the following files:

Appendix 2 - Disclosure

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