Trick or Treat

Summary

The SpookySwap contract has a design that could lead to an expensive loop vulnerability involving treats stored in the treatNames array. As new treats are added, treatNames grows in size, increasing the computational cost of any function that iterates through this array. Without constraints on the number of treats or optimized handling, this could result in significant gas costs or even failed transactions as the array size increases. This vulnerability impacts contract scalability and usability, potentially deterring user interaction due to high gas costs or out-of-gas errors.

Vulnerability Details

Key Issue:

• The treatNames array is updated each time a new treat is added, but it is not limited or optimized for size. If a function requires iterating over all treats (e.g., for retrieval or management), the cost of this loop scales linearly with the number of treats, potentially making the function prohibitively expensive.

Example Scenario:

1. Initial Setup: The contract owner adds numerous treats, significantly increasing the size of treatNames.

2. Execution: A function that needs to access or modify treat data attempts to loop through treatNames.

3. Outcome: As the array grows, the loop becomes too costly to complete within Ethereum’s block gas limit, leading to high gas fees or failed transactions.

Impact

• Gas Limit Exceedance: Functions that loop over all treats may exceed Ethereum’s block gas limit as the array grows, causing transactions to fail.

• High Gas Costs: Even successful transactions may become extremely costly if they involve looping through a large number of treats.

• Reduced Usability and Scalability: High gas costs or failed transactions deter user interactions, limiting the contract’s scalability and user experience.

Tools Used

Manual Review.

Recommendations

To mitigate this vulnerability, consider the following strategies:

1. Avoid Full Array Loops: Minimize or eliminate any functions that require looping through the entire treatNames array. Where possible, use direct mapping references instead of looping.

2. Cap on Maximum Number of Treats: Consider setting a maximum limit on the number of treats that can be added or periodically clean up the array by removing outdated entries. This will help manage the size of treatNames and prevent excessive gas costs over time.