Unbounded Fee Inflation Breaks Game Balance and Locks Out Players

Description

• In the Last Man Standing game, each time a player claims the throne, the claimFee is increased by a percentage set at deployment through the variable feeIncreasePercentage. This mechanism is meant to gradually raise the entry cost and add tension to the game.

• However, the constructor only ensures feeIncreasePercentage <= 100, which allows a 100% increase — effectively doubling the claimFee at each call:

• This leads to exponential growth (e.g., 0.5 ETH → 1 → 2 → 4 → 8 ...), pricing out most participants after just a few rounds. Since no upper bound or economic cap exists, the throne becomes unaffordable, and game rounds can lock themselves.

• Although the contract includes a resetGame() function, only the owner can invoke it, and it resets the round after a winner has been declared, not during a live game. Therefore, it does not mitigate the fact that individual rounds can become inaccessible, or that whales can dominate early with no viable competition.

Risk

Likelihood:

• The issue will occur in any deployment where feeIncreasePercentage is too high (e.g., ≥ 50), especially if many players interact in a short time.

• It is deterministic and accumulative with every call to claimThrone.

Impact:

• Rounds can become economically inaccessible after a few claims.

• The escalation mechanic becomes abusive rather than challenging.

• Early players or wealthy addresses can dominate and crowd out others.

• The game logic of Last Man Standing (progressive but fair competition) is broken.

Proof of Concept

Add this Proof of Code into Game.t.sol that proves that with 100% fee increase the claimThrone become rapidly very expensive.

Recommended Mitigation

Mitigation should target the root cause: unbounded configuration of feeIncreasePercentage, and optionally, introduce caps for claimFee.

Option 1: Restrict feeIncreasePercentage

Option 2 (optional): Add max claim fee cap