Eggstravaganza
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Submission Details
Severity: high
Valid

Insecure Pseudo-Random Number Generation in EggHuntGame

roccomania

Summary

The EggHuntGame contract uses a predictable method to generate pseudo-random numbers for determining whether a player finds an egg. This vulnerability allows miners or attackers to manipulate the outcome by controlling block variables (block.timestamp, block.prevrandao), leading to unfair advantages in the game.

Vulnerability Details

Location:
EggHuntGame::searchForEgg()

Issue:
The randomness is derived from:

uint256 random = uint256(
keccak256(abi.encodePacked(block.timestamp, block.prevrandao, msg.sender, eggCounter))
) % 100;

  • Predictability: block.timestamp and block.prevrandao are public and can be influenced by miners/validators.

  • Front-running Risk: Attackers can compute the expected random number before submitting a transaction and only proceed if favorable.

  • No Entropy: The seed lacks external unpredictability (e.g., oracle inputs).

Impact

Attackers can guarantee egg discoveries, breaking game fairness -- making them monopolize rewards, devaluing NFTs for legitimate participants.

Tools Used

  • Manual code review.

Recommendations

Use Chainlink VRF
Integrate Chainlink’s Verifiable Random Function (VRF) for cryptographically secure randomness.

Updates

Lead Judging Commences

m3dython Lead Judge 4 months ago
Submission Judgement Published
Validated
Assigned finding tags:

Insecure Randomness

Insecure methods to generate pseudo-random numbers

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