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

H-02

anierobipaschal70

Root + Impact

EIP-712 MESSAGE_TYPEHASH contains a typo (addres) and illegal space, permanently breaking all signature verification

Description

  • The MESSAGE_TYPEHASH constant contains two errors: the word address is misspelled as addres, and there is an illegal space after the comma. This produces a completely different keccak256 hash than any correctly-implemented off-chain signer would generate, making signature verification impossible.Risk

Likelihood:

  • This is a compile-time constant baked into the contract bytecode. Every single call to claimSnowman() uses this broken hash.

  • Any off-chain signing library implementing EIP-712 correctly will generate a structurally valid hash that will never match the contract's malformed hash.

Impact:

  • 100% of airdrop claims revert with SA__InvalidSignature. The entire Snowman NFT airdrop is permanently bricked.

Proof of Concept

Explanation: This PoC demonstrates the vulnerability by hashing both the correct EIP-712 string and the contract's broken string, explicitly showing that they produce different bytes32 values, meaning valid off-chain signatures will always be rejected.

function testTypehashMismatchBlocksAllClaims() public {
bytes32 correctHash = keccak256("SnowmanClaim(address receiver,uint256 amount)");
bytes32 brokenHash = keccak256("SnowmanClaim(addres receiver, uint256 amount)");
assertTrue(correctHash != brokenHash);
}
​

Recommended Mitigation

Explanation: The mitigation corrects the spelling of "address" and removes the illegal space after the comma to comply strictly with the EIP-712 hashing standard.

- 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 10 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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