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

SnowmanAirdrop MESSAGE_TYPEHASH is malformed ("addres" and stray spaces), so standards-compliant EIP-712 signatures are rejected

jengreg

Root + Impact

Description

  • The EIP-712 type string is malformed: address is misspelled as addres, and the string contains spaces that the EIP-712 encodeType format does not allow. The contract is internally self-consistent (it signs and verifies with the same constant), but the digest it produces is not the standard EIP-712 digest, so signatures from compliant tooling do not match.

// src/SnowmanAirdrop.sol
@> bytes32 private constant MESSAGE_TYPEHASH = keccak256("SnowmanClaim(addres receiver, uint256 amount)");
// ^^^^^^ typo + spaces; should be:
// "SnowmanClaim(address receiver,uint256 amount)"

Risk

Likelihood: Any user signing through a standards-compliant wallet (eth_signTypedData_v4, ethers signTypedData) reconstructs the typehash from the correctly spelled type and signs a different digest, which _isValidSignature rejects.

Impact: The delegated-claim feature is unusable through normal typed-data tooling; only a signer that signs the raw digest returned by getMessageHash works. No funds are at risk, so this is a standards-compliance and usability defect.

Proof of Concept

Self-contained Foundry test. It builds the claim digest exactly as a standards-compliant EIP-712 wallet would (using the correctly spelled typehash) and signs it. The contract verifies against its malformed digest, so the correct signature is rejected with SA__InvalidSignature.

// The CORRECT EIP-712 type string a compliant wallet uses (no typo, no spaces).
bytes32 constant CORRECT_TYPEHASH = keccak256("SnowmanClaim(address receiver,uint256 amount)");
bytes32 constant DOMAIN_TYPEHASH =
keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)");
​
function testCompliantSignatureIsRejected() public {
deal(address(snow), alice, 1);
​
// Build the digest exactly as eth_signTypedData_v4 / ethers signTypedData would.
bytes32 domainSeparator = keccak256(
abi.encode(DOMAIN_TYPEHASH, keccak256(bytes("Snowman Airdrop")), keccak256(bytes("1")),
block.chainid, address(airdrop))
);
bytes32 structHash = keccak256(abi.encode(CORRECT_TYPEHASH, alice, uint256(1)));
bytes32 compliantDigest = keccak256(abi.encodePacked("\x19\x01", domainSeparator, structHash));
​
(uint8 v, bytes32 r, bytes32 s) = vm.sign(aliceKey, compliantDigest);
​
// The contract verifies against its MALFORMED digest, so a correct signature fails.
bytes32[] memory emptyProof = new bytes32[](0);
vm.expectRevert(SnowmanAirdrop.SA__InvalidSignature.selector);
airdrop.claimSnowman(alice, emptyProof, v, r, s);
}

Result: [PASS] testCompliantSignatureIsRejected().

Recommended Mitigation

Correct the EIP-712 type string to the canonical form (fix the addres typo and remove the spaces) so the contract computes the standard digest and signatures from compliant wallets verify.

- 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 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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