Snowman Merkle Airdrop
AI First Flight #10
Beginner FriendlyFoundrySolidityNFT
EXP
View results
Previous Next
Submission Details
Severity: high
Valid

The SnowmanAirdrop contract defines a MESSAGE_TYPEHASH that does not conform to the standard EIP-712 type declaration, causing signature verification inconsistencies.

avengerabhay91290

Root + Impact

Description:

. A minor typographical inconsistency is present in the MESSAGE_TYPEHASH declaration of the SnowmanAirdrop contract.

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

Impact:

`function claimSnowman` never be `TRUE` condition

Risk

Likelihood: High

  • Off-chain signature generation using standard EIP-712 tooling always produces a digest that differs from the one computed on-chain due to the mismatched MESSAGE_TYPEHASH.

  • Signature verification logic consistently evaluates to invalid, causing every call to claimSnowman() to revert regardless of the signer or provided proof.

Impact:

  • Impact severity mapping (High vs Critical).

  • A one-line risk summary for report tables.

  • Full Likelihood × Impact matrix wording.

Proof of Concept

​
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

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

Lead Judging Commences

ai-first-flight-judge Lead Judge 1 day ago
Submission Judgement Published
Validated
Assigned finding tags:

[H-02] Unconsistent `MESSAGE_TYPEHASH` with standart EIP-712 declaration on contract `SnowmanAirdrop`

# Root + Impact ## Description * Little typo on `MESSAGE_TYPEHASH` Declaration on `SnowmanAirdrop` contract ```Solidity // 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` ```Solidity 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: ```diff - bytes32 private constant MESSAGE_TYPEHASH = keccak256("SnowmanClaim(addres receiver, uint256 amount)"); + bytes32 private constant MESSAGE_TYPEHASH = keccak256("SnowmanClaim(address receiver, uint256 amount)"); ```

Support

FAQs

Can't find an answer? Chat with us on Discord, Twitter or Linkedin.

Give us feedback!