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

Typo in MESSAGE_TYPEHASH Breaks All ERP-712 Signature Verifications

seenu1947

Root + Impact

The MESSAGE_TYPEHASH constant contains a typo where "address" is misspelled as "addres", causing all EIP-712 signature verifications to fail. This renders the entire airdrop system non-functional as no user can successfully claim Snowman NFTs.

The EIP-712 standard requires exact matching of type strings between off-chain signing and on-chain verification. When users generate signatures off-chain using the correct type string "SnowmanClaim(address receiver, uint256 amount)", the on-chain contract computes a different hash using the misspelled version, resulting in signature verification failure.

// src/SnowmanAirdrop.sol:49
bytes32 private constant MESSAGE_TYPEHASH = keccak256("SnowmanClaim(addres receiver, uint256 amount)");
// @> Typo: "addres" instead of "address"

Risk

Likelihood:

  • Every single claim attempt will fail signature verification

  • The typo is in a constant that is used for all signature validations

  • Users cannot bypass this check as it's fundamental to the claim process

Impact:

  • Complete system failure - no user can claim airdrops

  • All Snow tokens intended for claiming become locked

  • Airdrop campaign cannot proceed

  • Requires contract redeployment to fix

Proof of Concept

// Off-chain signature generation (correct)
const types = {
SnowmanClaim: [
{ name: 'receiver', type: 'address' }, // Correct spelling
{ name: 'amount', type: 'uint256' }
]
};
const signature = await signer._signTypedData(domain, types, value);
​
// On-chain verification (incorrect)
bytes32 MESSAGE_TYPEHASH = keccak256("SnowmanClaim(addres receiver, uint256 amount)");
// Hash mismatch → signature verification fails
​
// Test scenario:
function testClaimFailsDueToTypo() public {
// 1. User generates valid signature with correct type
// 2. Calls claimSnowman() with valid proof and signature
// 3. Transaction reverts with SA__InvalidSignature()
// Expected: Claim succeeds
// Actual: Always fails
}

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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