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

Incorrect EIP-712 typehash rejects standard delegated claim signatures

spacerubberducky

Root + Impact

The delegated claim flow is intended to let a receiver sign an EIP-712 SnowmanClaim message so another caller can submit claimSnowman() on the receiver's behalf.

The issue is that MESSAGE_TYPEHASH is not the canonical type hash for the SnowmanClaim struct. It misspells address as addres and includes a space after the comma.

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

The expected canonical EIP-712 type string is:

SnowmanClaim(address receiver,uint256 amount)

As a result, normal wallets and integrations that sign the intended typed data produce signatures that claimSnowman() rejects.

Risk

Likelihood

High. This occurs whenever a user signs the standards-compliant typed-data struct instead of reproducing the contract typo exactly. Normal EIP-712 tooling will use the canonical field type address, not addres.

Impact

Medium. The advertised delegated claim flow is broken for standard off-chain signers. A gas payer cannot claim on behalf of a receiver using a normal EIP-712 signature. Integrators must know and duplicate the typo to make signatures pass, which defeats the expected interoperability of EIP-712.

Proof of Concept

Add this test to test/SnowmanFindings.t.sol:

function testStandardsCompliantEip712SignatureIsRejected() public {
bytes32[] memory proof = _aliceProof();
bytes32 standardDigest = _standardDigest(alice, 1);
(uint8 v, bytes32 r, bytes32 s) = vm.sign(aliceKey, standardDigest);
​
vm.prank(alice);
snow.approve(address(airdrop), 1);
​
vm.prank(gasPayer);
vm.expectRevert(SnowmanAirdrop.SA__InvalidSignature.selector);
airdrop.claimSnowman(alice, proof, v, r, s);
}

Run:

forge test --match-test testStandardsCompliantEip712SignatureIsRejected -vv

The test passes. A canonical EIP-712 digest for SnowmanClaim(address receiver,uint256 amount) is signed by Alice, but claimSnowman() reverts with SA__InvalidSignature.

Recommended Mitigation

Use the canonical EIP-712 type string without the typo and without the extra space.

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

Add a test that signs the canonical EIP-712 struct and confirms claimSnowman() accepts it.

Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge about 22 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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