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

Malformed EIP-712 type string in SnowmanAirdrop::MESSAGE_TYPEHASH (addres typo + spaces) breaks signature compatibility with standard tooling

colddecemberrrr

Root + Impact: the EIP-712 type string is misspelled and spaced incorrectly, so signatures produced by any standard EIP-712 signer fail verification.

Description

  • The EIP-712 encodeType string for the claim struct must be exactly SnowmanClaim(address receiver,uint256 amount).

  • MESSAGE_TYPEHASH misspells address as addres and adds spaces, producing a non-standard typehash. The contract is internally consistent, but any external signer that hashes the correct type string produces a signature that does not match.

bytes32 private constant MESSAGE_TYPEHASH =
@> keccak256("SnowmanClaim(addres receiver, uint256 amount)"); // "addres" typo + invalid spaces

Risk

Likelihood:

  • Occurs whenever a recipient signs the claim using standard EIP-712 tooling (wallet eth_signTypedData, ethers/viem signTypedData), which encodes the correct type string and yields a non-matching signature that reverts with SA__InvalidSignature.

Impact:

  • Breaks interoperability with all standard EIP-712 signers; integrators must reproduce the malformed string to make gasless claims work.

  • Defeats the purpose of EIP-712 (wallet-native, human-readable typed-data signing) and is a foot-gun for downstream tooling.

Proof of Concept

// The on-chain constant differs from the EIP-712-compliant typehash that any
// standard signer would use, so their signature will not verify:
bytes32 onchain = keccak256("SnowmanClaim(addres receiver, uint256 amount)");
bytes32 standard = keccak256("SnowmanClaim(address receiver,uint256 amount)");
assert(onchain != standard); // signatures built against `standard` revert as SA__InvalidSignature

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 about 5 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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