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

EIP-712 Compatibility Break via Typo in MESSAGE_TYPEHASH

shahparv1310

Description

Normal Behavior

The SnowmanAirdrop contract should implement EIP-712 compliant signature verification using the correct type hash that matches the SnowmanClaim struct definition.

Issue Description

The MESSAGE_TYPEHASH constant contains a typo "addres" instead of "address", breaking EIP-712 compatibility and causing signature verification to fail with standard implementations.

Root + Impact

Description

The contract implements EIP-712 signature verification but uses an incorrect type hash due to a spelling error, making the signature system incompatible with standard EIP-712 implementations.

Root Cause

// @> Critical: Typo in MESSAGE_TYPEHASH breaks EIP-712 compatibility
struct SnowmanClaim {
address receiver;
uint256 amount;
}
​
bytes32 private constant MESSAGE_TYPEHASH = keccak256("SnowmanClaim(addres receiver, uint256 amount)");
// @> Typo: "addres" should be "address"

The getMessageHash() function uses this incorrect typehash for EIP-712 message signing 2 , and _isValidSignature() verifies the resulting digest 3 .

Risk

Likelihood:

  • Reason 1: The typo is present in the deployed constant and affects all signature operations

  • Reason 2: Standard EIP-712 libraries will generate different type hashes, causing verification failures

Impact:

  • Impact 1: Signature verification fails for all legitimate users trying to claim with standard EIP-712 implementations

  • Impact 2: Complete breakdown of the signature-based authentication system, preventing all claims

Proof of Concept

function testEIP712CompatibilityBreak() public {
// Standard EIP-712 implementation generates correct typehash
bytes32 correctTypehash = keccak256("SnowmanClaim(address receiver, uint256 amount)");
// Contract uses incorrect typehash due to typo
bytes32 contractTypehash = airdrop.MESSAGE_TYPEHASH();
// Typehashes don't match - EIP-712 incompatibility
assertTrue(correctTypehash != contractTypehash);
// User tries to claim with standard EIP-712 signature
vm.startPrank(user);
(uint8 v, bytes32 r, bytes32 s) = _signMessage(userPrivateKey, getMessageHash(user));
// Signature verification fails due to typehash mismatch
vm.expectRevert(SnowmanAirdrop.SA__InvalidSignature.selector);
airdrop.claimSnowman(user, validProof, v, r, s);
}

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 3 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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