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

MESSAGE_TYPEHASH Typo

bravejoy780

Root + Impact

Description

The EIP-712 signature verification requires exact type matching between off-chain signing and on-chain verification for cryptographic validity. The MESSAGE_TYPEHASH contains a typo (addres instead of address), causing hash mismatch between user signatures and contract verification.

// Root cause in the codebase with @> marks to highlight the relevant section

Risk

Likelihood: HIGH

  • Every single claim transaction will hit signature verification, making this bug execute 100% of the time.

  • No conditional logic protects this - it's a constant used in all claim flows.

  • Users cannot work around this issue as the hash is hardcoded in the contract.

  • Bug is deterministic and will affect every single user attempting to claim.

Impact: CRITICAL

  • Complete denial of service - zero claims can ever succeed due to signature verification failure.

  • All airdrop NFTs permanently locked in contract with no distribution possible.

  • Contract must be redeployed, losing gas costs and requiring new merkle tree generation.

  • User trust and project reputation severely damaged due to non-functional airdrop.

  • Potential loss of users who signed messages that become invalid after redeployment.

Proof of Concept

  • User signs message off-chain using correct type string, contract hashes incorrect type string internally.

  • Hash mismatch causes all signature verifications to fail, reverting every claim with SA__InvalidSignature().

function test_SignatureAlwaysFails() public {
// User signs with correct type off-chain
bytes32 correctHash = keccak256("SnowmanClaim(address receiver, uint256 amount)");
// Contract uses wrong type
bytes32 contractHash = keccak256("SnowmanClaim(addres receiver, uint256 amount)");
assert(correctHash != contractHash); // Always different
// Result: All claims revert with SA__InvalidSignature()
}

Recommended Mitigation

Fix the typo by changing addres to address in the MESSAGE_TYPEHASH constant declaration.

-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 13 days 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)"); ```

Support

FAQs

Can't find an answer? Chat with us on Discord, Twitter or Linkedin.

Give us feedback!