Mystery Box

Summary

The addReward function in the MysteryBox contract was identified as vulnerable to a lack of input validation, allowing the addition of rewards with invalid or misleading values. This vulnerability could lead to scenarios where users are deceived into believing they have earned valuable rewards when, in reality, the reward value might be zero or the name could be an empty string. Tests confirmed that without proper validation, malicious or careless inputs could introduce rewards that mislead users. This report highlights the risks associated with inadequate input validation and demonstrates how to enforce proper constraints to ensure the integrity of smart contract data.

Vulnerability Details

The addReward function lacked validation checks to ensure that rewards added to the contract had meaningful values and non-empty names. As a result, it was possible to introduce rewards with a value of zero or with an empty string as the reward name, creating confusion for users.

Details:

• Absence of Input Validation: The function did not validate that the reward's value was greater than zero or that the reward's name was non-empty.

• Impact: Malicious actors or careless inputs could add worthless rewards or misleading entries to the reward pool, causing users to mistakenly believe they had earned valuable rewards.

Code Analysis

Original addReward Function:

Key Issues:

• The function allowed any string or value to be passed, including empty strings for _name or a value of 0 for _value.

Mitigated Version with Input Validation

Key Strength:

• By enforcing the requirement that _value must be greater than zero and _name must not be an empty string, the function now prevents the addition of misleading or worthless rewards.

Proof of Concept (PoC)

1. Before Mitigation: Tests were conducted to simulate the addition of invalid rewards. The function allowed adding a reward with an empty name and a reward with a value of zero, demonstrating the lack of input validation.

Results:

• Before Mitigation: The tests showed that the contract accepted rewards with an empty name and a value of zero, demonstrating the lack of proper validation.

1. After Mitigation: The tests were repeated after implementing input validation, and attempts to add rewards with invalid values resulted in reverted transactions, as expected.

Results:

• The mitigation successfully prevented the addition of rewards with invalid values, confirming that the input validation works as intended.

Impact

• Prevention of Misleading Rewards: The original implementation allowed adding misleading or worthless rewards, which could have confused users or been exploited maliciously.

• Effective Mitigation: The addition of input validation prevents such scenarios, ensuring that all rewards added to the contract are valid and meaningful.

Tools Used

• Manual code analysis

• Foundry for testing the input validation vulnerability

Recommendations

1. Always Validate User Input: Implement checks for input values in all functions, especially those that modify state variables, to prevent unwanted or malicious data from being introduced.

2. Conduct Thorough Testing: Use testing frameworks like Foundry to simulate different scenarios and ensure that input validation functions as intended.

3. Monitor Reward Pool Integrity: Regularly audit the contents of critical data structures like rewardPool to maintain data integrity.

Conclusion

The addReward function was vulnerable due to a lack of input validation, allowing the introduction of rewards with empty names or zero values. By implementing input validation, this vulnerability was successfully mitigated, ensuring that only meaningful and valid rewards can be added to the contract. This serves as a reminder of the importance of validating all user inputs in Ethereum smart contracts to maintain data integrity and prevent exploitation.