Rock Paper Scissors

Summary

joinGameWithEth does not check whether the game the player is about to join was created with ETH.

Vulnerability Details

In createGameWithToken, game.bet is set to 0 when creating a game with token,

In joinGameWithEth, we do not check if the game we are joining is a game created by eth. Thus, we can use joinGameWithEth to enter into a game created by a token.

For example,

1. PlayerA creates a game using createGameWithToken using a token.

2. Attacker joins this game by calling joinGameWithEth with msg.value set to 0.

Impact

A player can join a game without paying any tokens. This eventually causes the game creator (playerA) to lose money, leading to a severe disruption of functionality.

Tools Used

VSCode

Recommendations

In joinGameWithEth, add a check to see if the game is created with Eth,