Snowman Merkle Airdrop
AI First Flight #10
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EXP
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Submission Details
Severity: high
Valid

EIP-712 MESSAGE_TYPEHASH Contains Typo Breaking Signature Verification

sharonkosgei4

Root + Impact

Description

  • Normal behavior: The EIP-712 typehash should use correct type names so that signatures generated by external tools (wallets, dApps) match what the contract expects.

  • Specific issue: The MESSAGE_TYPEHASH constant contains a typo - "addres" instead of "address". This causes the contract to compute a different hash than what standard EIP-712 compliant signers would compute.

// Root cause in src/SnowmanAirdrop.sol:49
bytes32 private constant MESSAGE_TYPEHASH =
@> keccak256("SnowmanClaim(addres receiver, uint256 amount)");
// ^^^^^^ TYPO: "addres" should be "address"
​

Risk

Likelihood:

  • Every signature generated using correct EIP-712 tooling will fail verification

  • The typo is in a constant, affecting all claim operations

Impact:

  • External signers using proper EIP-712 implementations will produce invalid signatures

  • Breaks interoperability with standard wallet signing flows

  • Users must use the malformed typehash to generate valid signatures, violating the EIP-712 spec

Proof of Concept

  • The following test demonstrates that the typo in the typehash ("addres" vs "address") produces two completely different hash values. Any signature generated using the correct EIP-712 spelling will fail verification because the contract uses the malformed typehash.

function test_TypehashTypo() public {
bytes32 wrongTypehash = keccak256("SnowmanClaim(addres receiver, uint256 amount)");
bytes32 correctTypehash = keccak256("SnowmanClaim(address receiver, uint256 amount)");
​
// These are different hashes - signatures won't match!
assertTrue(wrongTypehash != correctTypehash);
​
// Wrong: 0xff59e96f4a12fdaf4e417a1440b578f822f6cb542be1a2a7c196280bec54f9ab
// Correct: 0x6cedfa9a039e959a5fe5a6e4224acac28bb707e70fb8ad28e3ac109c88b280d6
}

Recommended Mitigation

Fix the typo in the MESSAGE_TYPEHASH constant by changing "addres" to "address". This ensures the contract computes the same hash as standard EIP-712 compliant signing tools.

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

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