ABI encodePacked Collision SLITHER-W1004

Detect collision due to dynamic type usages in abi.encodePacked

Exploit Scenario

contract Sign {
    function get_hash_for_signature(string name, string doc) external returns(bytes32) {
        return keccak256(abi.encodePacked(name, doc));
    }
}

Bob calls get_hash_for_signature with (bob, This is the content). The hash returned is used as an ID. Eve creates a collision with the ID using (bo, bThis is the content) and compromises the system.

Recommendation

Do not use more than one dynamic type in abi.encodePacked() (see the Solidity documentation). Use abi.encode(), preferably.

Learn more

encode-packed-collision on Slither's wiki.