TwentyOne

Summary

The playersHand() and dealersHand() functions always value Aces as 1, ignoring the standard blackjack rule that Aces can be 1 or 11. This limits strategic play and diverges from standard gameplay.

Vulnerability Details

• Issue: Aces (cardValue == 1) are always counted as 1.

• Affected Code Snippet:

  // Aces are added as 1 without flexibility

  playerTotal += cardValue;

• Explanation: There's no logic to adjust the Ace's value to 11 when it benefits the hand total.

Impact

• Reduced Strategic Depth: Players can't utilize the flexibility of Aces.

• Deviation from Standard Rules: The game doesn't align with typical blackjack, possibly affecting player satisfaction.

Tools Used

• Manual code review of playersHand() and dealersHand() functions.

Recommendations

• Implement Flexible Ace Valuation:

  uint256 aceCount = 0;

  // When counting cards

  if (cardValue == 1) {

  playerTotal += 11;

  aceCount += 1;

  }

  // After summing cards

  while (playerTotal > 21 && aceCount > 0) {

  playerTotal -= 10;

  aceCount -= 1;

  }

• Apply to Both Functions: Ensure both player and dealer hands handle Aces flexibly.

• Add Tests: Create tests for hands with Aces to verify correct totals.