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

MESSAGE_TYPEHASH typo 'addres' breaks EIP-712 signature verification for all standard signers

hatchworker

MESSAGE_TYPEHASH typo 'addres' breaks EIP-712 signature verification for all standard signers

Summary

The EIP-712 struct typehash used by getMessageHash() is derived from the misspelled type string "SnowmanClaim(addres receiver, uint256 amount)" (note: addres, missing the second s). Any signer following the EIP-712 standard — a wallet via eth_signTypedData_v4, ethers' _signTypedData, or any compliant frontend — derives the typehash from the correctly spelled type string "SnowmanClaim(address receiver, uint256 amount)" and produces a digest that can never equal getMessageHash()'s output. A legitimately signed claim therefore always reverts with SA__InvalidSignature inside claimSnowman.

Vulnerability Details

Location: src/SnowmanAirdrop.sol:55:

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

"Self-consistent" is not a defense: the repo's own Foundry tests sign getMessageHash() output directly, which is why the typo is invisible there. In production, the type string is a public standard interface — every real-world signer speaks the correct spelling. This cannot be fixed by signers or frontends; the contract itself must use the canonical type string.

Impact

The signature-gated claim path is broken for every standards-compliant signer; the entire gasless-claim design (the point of the EIP-712 flow) does not work as specified. Likelihood High: every user signing through a normal wallet hits it; only direct on-chain getMessageHash() consumers are unaffected.

Proof of Concept

PoC file: PoC2_CanonicalMisses.t.sol (attached to this submission). The test test_PoC_TypehashTypoBreaksStandardSigners:

  1. Reconstructs the EIP-712 digest exactly as a compliant signer would (canonical typehash + same domain),

  2. Proves digest != airdrop.getMessageHash(alice),

  3. Signs the canonical digest with alice's key and shows claimSnowman reverts with SA__InvalidSignature.

Result: PASS — the canonical signer digest never matches the contract's digest, so the claim always reverts.

Recommendation

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