Sparkn

Summary

Using encode packed in not eip712 compliant and the use of encodePacked can cause hash collions.

Vulnerability Details

From the solidity Docs we can see a warning
https://docs.soliditylang.org/en/v0.8.17/abi-spec.html?highlight=collisions#non-standard-packed-mode

If you use keccak256(abi.encodePacked(a, b)) and both a and b are dynamic types, it is easy to craft collisions in the hash value by moving parts of a into b and vice-versa. More specifically, abi.encodePacked("a", "bc") == abi.encodePacked("ab", "c")

Additionally in the open zeppelin docs it states that use of keccak256 and encode(not packed) are acceptable, but never states that encodePacked is acceptable.
https://docs.openzeppelin.com/contracts/3.x/api/drafts#EIP712

The encoding specified in the EIP is very generic, and such a generic implementation in Solidity is not feasible, thus this contract does not implement the encoding itself. Protocols need to implement the type-specific encoding they need in their contracts using a combination of abi.encode and keccak256.

Impact

Possible hash collions when using encodePacked, and not eip712 compliant

Tools Used

manual review

Recommendations

do not use encode packed