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

Misspelled EIP-712 type hash rejects standard wallet signatures

mythdd

Root + Impact

Description

  • Normal behavior: receivers should be able to sign a standard EIP-712 typed-data message for SnowmanClaim(address receiver,uint256 amount), and relayers should be able to submit that signature to claim on their behalf.

  • The issue is that the contract hashes SnowmanClaim(addres receiver, uint256 amount), where address is misspelled as addres and the type string also includes non-canonical spacing. Standard EIP-712 tools and wallets produce a different digest for the valid struct type, so signatures created with the expected typed-data schema are rejected by the contract.

struct SnowmanClaim {
address receiver;
uint256 amount;
}
​
// @> "address" is misspelled as "addres"; the canonical EIP-712 type string is not used.
bytes32 private constant MESSAGE_TYPEHASH = keccak256("SnowmanClaim(addres receiver, uint256 amount)");
​
function getMessageHash(address receiver) public view returns (bytes32) {
if (i_snow.balanceOf(receiver) == 0) {
revert SA__ZeroAmount();
}
​
uint256 amount = i_snow.balanceOf(receiver);
​
return _hashTypedDataV4(
keccak256(abi.encode(MESSAGE_TYPEHASH, SnowmanClaim({receiver: receiver, amount: amount})))
);
}

Risk

Likelihood:

  • Wallets and frontend libraries encode typed data with the valid primitive type address, not the invalid primitive addres.

  • Every claim path calls _isValidSignature(receiver, getMessageHash(receiver), v, r, s), so all relayed claims depend on this digest.

Impact:

  • Standard wallet signatures for the documented claim type fail with SA__InvalidSignature.

  • The intended gas-sponsored claim flow can become unusable unless off-chain infrastructure signs the contract's non-standard raw digest.

Proof of Concept

The test builds the digest that a standard EIP-712 wallet would sign for SnowmanClaim(address receiver,uint256 amount). The contract rejects that signature because it verifies against the misspelled internal type string instead of the canonical EIP-712 type.

function testStandardEip712SignatureIsRejectedBecauseTypeHashIsMisspelled() public {
(SnowmanAirdrop airdrop, Snow snow,) = _deployAirdrop();
(address alice, uint256 aliceKey) = makeAddrAndKey("alice");
​
vm.prank(alice);
snow.approve(address(airdrop), 1);
​
(bytes1 fields, string memory name, string memory version, uint256 chainId, address verifyingContract, bytes32 salt,)
= airdrop.eip712Domain();
bytes32 domainSeparator =
MessageHashUtils.toDomainSeparator(fields, name, version, chainId, verifyingContract, salt);
bytes32 standardTypeHash = keccak256("SnowmanClaim(address receiver,uint256 amount)");
bytes32 standardStructHash = keccak256(abi.encode(standardTypeHash, alice, snow.balanceOf(alice)));
bytes32 standardDigest = MessageHashUtils.toTypedDataHash(domainSeparator, standardStructHash);
​
(uint8 v, bytes32 r, bytes32 s) = vm.sign(aliceKey, standardDigest);
​
vm.expectRevert(SnowmanAirdrop.SA__InvalidSignature.selector);
airdrop.claimSnowman(alice, AL_PROOF, v, r, s);
}

Recommended Mitigation

Use the canonical EIP-712 type string and keep the off-chain typed-data schema identical.

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

Regenerate any frontend, script, and test fixtures that sign the claim message so they use the corrected type.

Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge about 2 hours 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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