Snowman Merkle Airdrop
First Flight #42
Beginner FriendlyFoundrySolidityNFT
100 EXP
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Submission Details
Severity: low
Valid

No Duplicate Claim Check (Missing Claimed State)

jufel

Description: The 'claimSnowman' function does not track whether a user has already claimed their Snowman NFT.

Impact: A user can call 'claimSnowman' multiple times with the same valid Merkle proof and signature, repeatedly minting Snowman NFTs and draining the system.

Proof of Concept: Include the following test in the TestSnowmanAirdrop.t.sol file:

function testDoubleClaim() public {
vm.prank(alice);
snow.approve(address(airdrop), 2);
​
bytes32 alDigest = airdrop.getMessageHash(alice);
​
(uint8 alV, bytes32 alR, bytes32 alS) = vm.sign(alKey, alDigest);
​
airdrop.claimSnowman(alice, AL_PROOF, alV, alR, alS);
​
vm.warp(block.timestamp + 1 weeks);
vm.prank(alice);
snow.earnSnow();
​
airdrop.claimSnowman(alice, AL_PROOF, alV, alR, alS);
​
assert(nft.balanceOf(alice) == 2);
}

Recommended Mitigation: Track claim status:

function claimSnowman(address receiver, bytes32[] calldata merkleProof, uint8 v, bytes32 r, bytes32 s)
external
nonReentrant
{
+ if (s_hasClaimedSnowman[receiver]) {
+ revert("Already claimed");
+ }
​
// ...
}
Updates

Lead Judging Commences

yeahchibyke Lead Judge 3 months ago
Submission Judgement Published
Validated
Assigned finding tags:

Lack of claim check

The claim function of the Snowman Airdrop contract doesn't check that a recipient has already claimed a Snowman. This poses no significant risk as is as farming period must have been long concluded before snapshot, creation of merkle script, and finally claiming.

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