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

malformed-eip-712-typehash-rejects-standard-claim-signatures

zengsimin621

Root + Impact

Description

  • EIP-712 signatures should be generated from the canonical Solidity struct type string so wallets, frontends, relayers, and contracts compute the same digest.

  • MESSAGE_TYPEHASH uses the malformed string SnowmanClaim(addres receiver, uint256 amount), which misspells address and includes a non-canonical space, so standard EIP-712 signatures are rejected.

contract SnowmanAirdrop is EIP712, ReentrancyGuard {
struct SnowmanClaim {
address receiver;
uint256 amount;
}
​
@> bytes32 private constant MESSAGE_TYPEHASH =
@> keccak256("SnowmanClaim(addres receiver, uint256 amount)");
​
function getMessageHash(address receiver) public view returns (bytes32) {
uint256 amount = i_snow.balanceOf(receiver);
@> return _hashTypedDataV4(
@> keccak256(abi.encode(MESSAGE_TYPEHASH, SnowmanClaim({receiver: receiver, amount: amount})))
);
}
}

Risk

Likelihood:

  • Users claim through wallets, frontends, relayers, or scripts that encode the declared EIP-712 struct with the canonical address type.

  • The contract verifies every claim against the malformed MESSAGE_TYPEHASH during claimSnowman.

Impact:

  • Otherwise eligible users are rejected with SA__InvalidSignature when they submit signatures produced by standard EIP-712 tooling.

  • Delegated claiming and wallet interoperability are broken for the airdrop.

Proof of Concept

function test_CB002_standardEip712SignatureIsRejected() public {
vm.prank(alice);
snow.approve(address(airdrop), 1);
​
bytes32 digest = canonicalDigest(alice, 1);
(uint8 v, bytes32 r, bytes32 s) = vm.sign(aliceKey, digest);
​
vm.expectRevert(SnowmanAirdrop.SA__InvalidSignature.selector);
airdrop.claimSnowman(alice, AL_PROOF, v, r, s);
}
​
function canonicalDigest(address receiver, uint256 amount) internal view returns (bytes32) {
bytes32 domainSeparator = keccak256(
abi.encode(
keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"),
keccak256(bytes("Snowman Airdrop")),
keccak256(bytes("1")),
block.chainid,
address(airdrop)
)
);
bytes32 structHash = keccak256(
abi.encode(keccak256("SnowmanClaim(address receiver,uint256 amount)"), receiver, amount)
);
return keccak256(abi.encodePacked("\x19\x01", domainSeparator, structHash));
}

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 4 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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