Biconomy: Nexus
Biconomy
HardhatFoundry
30,000 USDC
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Submission Details
Severity: low
Invalid

`EIP-712` Compatibility issue in `Nexus.sol`

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Summary

The current implementation of the replaySafeHash and _eip712Hash functions in the Nexus.sol contract does not conform to the EIP-712 standard, particularly in how dynamic types like bytes32 are handled. This causes signatures generated using standard EIP-712 tools to fail validation.

Vulnerability Details

The vulnerability lies in the direct usage of the hash parameter without properly encoding it as per EIP-712 requirements. According to EIP-712:

  • Dynamic types (bytes, string) should be hashed using keccak256 before being included in the final hash computation.

  • The current implementation directly uses hash instead of encoding it properly, which results in an incompatible hash structure.

https://github.com/Cyfrin/2024-07-biconomy/blob/9590f25cd63f7ad2c54feb618036984774f3879d/contracts/Nexus.sol#L339-L341

function replaySafeHash(bytes32 hash) public view virtual returns (bytes32) {
return _eip712Hash(hash);
}

https://github.com/Cyfrin/2024-07-biconomy/blob/9590f25cd63f7ad2c54feb618036984774f3879d/contracts/Nexus.sol#L367-L369

function _eip712Hash(bytes32 hash) internal view virtual returns (bytes32) {
return keccak256(abi.encodePacked("\x19\x01", _domainSeparator(), keccak256(abi.encode(_MESSAGE_TYPEHASH, hash))));
}

Impact

Signatures generated using common EIP-712 tools would fail validation when interacting with the Nexus.sol contract. This inconsistency undermines the security and reliability of signature verification processes.

Tools Used

Manual code review

Recommendations

  • Correct Encoding: Ensure that dynamic types (bytes32 in this case) are encoded using keccak256 before being included in the hash computation.

  • Update _eip712Hash Function: Modify the _eip712Hash function to correctly encode the hash parameter as per EIP-712 specifications.

Updates

Lead Judging Commences

0xnevi Lead Judge 12 months ago
Submission Judgement Published
Invalidated
Reason: Incorrect statement
Assigned finding tags:

finding-wrong-EIP712-encodeData

Invalid, `bytes32` is not a dynamic value as oppose to `bytes`, since it is exactly 32 bytes long, so the encoding is correct, no issues here that is inconsistent with the `encodeData` definition highlighted in EIP712. > The atomic values are encoded as follows: Boolean false and true are encoded as uint256 values 0 and 1 respectively. Addresses are encoded as uint160. Integer values are sign-extended to 256-bit and encoded in big endian order. bytes1 to bytes31 are arrays with a beginning (index 0) and an end (index length - 1), they are zero-padded at the end to bytes32 and encoded in beginning to end order. This corresponds to their encoding in ABI v1 and v2.

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