First Flight #10: One Shot

Summary

The event generated to publish the results of a battle and the actual result of said battle can differ, leading to events and actual results not matching.

Vulnerability Details

In rapBattle.sol::_battle, the outcome of a battle is determined twice:

• once to generate an event

• once to determine who should receive the prize of the battle

These two checks, however, differ, as one uses an inclusive comparison (<=), and the other a strict one (<).
The check to generate the event is

while the check to determine who receives the prize is

There is a clear, edge-case scenario where random is equal to defenderRapperSkill and these two checks end up returning opposite outcomes.

Impact

If the events are used for logging the outcomes of battles, there is a potential mismatch between the published results, via the event mechanism, and the actual winner, represented by the NFT owner that receives the prize.

Tools Used

Manual review, VSCode

Recommendations

The two checks should be equal, either both inclusive or both strict.