Summary

The giveReview function deducts 10 points from a student's score for every negative review without validating whether the subtraction would cause the score to drop below zero. This can cause the studentScore to underflow, wrapping around to a very large uint256 value, which may break logic dependent on valid score ranges or graduation conditions.

Vulnerability Details

Example Exploit:

1. A student has a score of 5.

2. A teacher submits a bad review.

3. studentScore becomes 2^256 - 5 (due to underflow in uint256).

4. This gives the student an extremely high score, potentially letting them bypass a cutoff or logic that checks for "top performers."

Impact

• Integrity Violation: Underflowing studentScore breaks the intended scoring logic.

• False Graduation: A student with a huge wrapped score could wrongly qualify for benefits (e.g., graduation).

• Review System Compromise: Undermines the credibility of the review system.

Tools Used

• Manual Code Review

• Solidity language semantics (uint256 arithmetic behavior pre-0.8 vs post-0.8)

• Domain knowledge of smart contract score/trust systems

Recommendations

Fixed Code

This ensures:

• Scores never drop below zero.

• Good reviews actually benefit students.

• Prevents exploit scenarios tied to arithmetic overflows/underflows.