President Elector

Summary

The function rankCandidatesBySig does not consider the current s_voteNumber or any sort of expiration time on the signature. A malicious actor can store signatures from a previous vote number and resubmit them for future votes to influence results.

Vulnerability Details

The function rankedCandidatesBySig copied above does not account for the current vote number. This means that a malicious actor can store previous signature, orderedCandidates inputs and re use them in future votes. If the TYPEHASH, orderedCandidatesare the same, the structHashwill be the same and the signature will be considered valid since the domain separator constructed in the EIP712 contract remains unchanged.

In particular, a sophisticated and motivated actor, such as the current president, could store results from the previous round where they won, and near the end of the voting time block replay all the votes that were in their favor to possibly swing the election towards them winning again. It may be possible to even bundle these transactions together and call selectPresident as the last transaction in the bundle to prevent anyone from noticing or stopping this sort of attack.

Impact

This is a HIGH impact vulnerability as it ruins the integrity of the voting process past the first round and breaks the core functionality of the contract.

Tools Used

Foundry

Recommendations

Include the s_voteNumber when creating the structHash. This will prevent replay in future rounds. A modified version of rankCandidatesBySig that protects against this is shown below.