ArkProject: NFT Bridge

Summary

The requestHash function in the Protocol.sol uses abi.encodePacked for encoding inputs before hashing with keccak256. This can lead to hash collisions if the input types and values are not unique enough, potentially causing different inputs to produce the same hash.

Vulnerability Details

The requestHash function is designed to compute a hash for a bridge request using the keccak256 hashing algorithm. The function uses abi.encodePacked to encode the inputs, which performs packed encoding. Packed encoding does not include length information or padding, making it open to hash collisions.

For example,lets consider the following two sets of inputs:

1. salt = 1, collection = 0x0000000000000000000000000000000000000001, toL2Address = 0x0000000000000000000000000000000000000001, tokenIds = [1, 2]

2. salt = 0, collection = 0x0000000000000000000000000000000000000001, toL2Address = 0x0000000000000000000000000000000000000001, tokenIds = [1, 2, 1]

Both of these inputs could produce the same packed encoding and thus the same hash, leading to a collision.

Impact

Incorrect identification of unique requests. It could also lead to potential replay attacks or unauthorized actions if different inputs produce the same hash and also potential loss of funds or other assets.

Tools Used

• Manual code review.

Recommendations

To avoid hash collisions, use abi.encode instead of abi.encodePacked.

By using abi.encode, you ensure that the inputs are encoded in a way that includes length information, reducing the risk of hash collisions.