Snowman Merkle Airdrop
First Flight #42
Beginner FriendlyFoundrySolidityNFT
100 EXP
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Submission Details
Impact: high
Likelihood: high

Unconsistent `MESSAGE_TYPEHASH` with standart EIP-712 declaration on contract `SnowmanAirdrop`

Author Revealed upon completion

Root + Impact

Description

  • Little typo on MESSAGE_TYPEHASH Declaration on SnowmanAirdrop contract

// src/SnowmanAirdrop.sol
​
49: bytes32 private constant MESSAGE_TYPEHASH = keccak256("SnowmanClaim(addres receiver, uint256 amount)");

Impact:

  • function claimSnowman never be TRUE condition

Proof of Concept

Applying this function at the end of /test/TestSnowmanAirdrop.t.sol to know what the correct and wrong digest output HASH.

Ran with command: forge test --match-test testFrontendSignatureVerification -vvvv

function testFrontendSignatureVerification() public {
// Setup Alice for the test
vm.startPrank(alice);
snow.approve(address(airdrop), 1);
vm.stopPrank();
// Simulate frontend using the correct format
bytes32 FRONTEND_MESSAGE_TYPEHASH = keccak256("SnowmanClaim(address receiver, uint256 amount)");
// Domain separator used by frontend (per EIP-712)
bytes32 DOMAIN_SEPARATOR = keccak256(
abi.encode(
keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"),
keccak256("Snowman Airdrop"),
keccak256("1"),
block.chainid,
address(airdrop)
)
);
// Get Alice's token amount
uint256 amount = snow.balanceOf(alice);
// Frontend creates hash using the correct format
bytes32 structHash = keccak256(
abi.encode(
FRONTEND_MESSAGE_TYPEHASH,
alice,
amount
)
);
// Frontend creates the final digest (per EIP-712)
bytes32 frontendDigest = keccak256(
abi.encodePacked(
"\x19\x01",
DOMAIN_SEPARATOR,
structHash
)
);
// Alice signs the digest created by the frontend
(uint8 v, bytes32 r, bytes32 s) = vm.sign(alKey, frontendDigest);
// Digest created by the contract (with typo)
bytes32 contractDigest = airdrop.getMessageHash(alice);
// Display both digests for comparison
console2.log("Frontend Digest (correct format):");
console2.logBytes32(frontendDigest);
console2.log("Contract Digest (with typo):");
console2.logBytes32(contractDigest);
// Compare the digests - they should differ due to the typo
assertFalse(
frontendDigest == contractDigest,
"Digests should differ due to typo in MESSAGE_TYPEHASH"
);
// Attempt to claim with the signature - should fail
vm.prank(satoshi);
vm.expectRevert(SnowmanAirdrop.SA__InvalidSignature.selector);
airdrop.claimSnowman(alice, AL_PROOF, v, r, s);
​
assertEq(nft.balanceOf(alice), 0);
}

Recommended Mitigation

on contract SnowmanAirdrop Line 49 applying this:

- bytes32 private constant MESSAGE_TYPEHASH = keccak256("SnowmanClaim(addres receiver, uint256 amount)");
+ bytes32 private constant MESSAGE_TYPEHASH = keccak256("SnowmanClaim(address receiver, uint256 amount)");

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