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

EIP-712 typehash typo in SnowmanAirdrop makes standard typed-data signatures always fail

keitt19

Root + Impact

Description

Normal behavior: claimSnowman() verifies that the claimant authorized the claim via an EIP-712 signature. The digest is built from MESSAGE_TYPEHASH, the domain separator, and the claim struct SnowmanClaim(address receiver, uint256 amount).

Specific issue: the typehash constant contains a typo — "addres" instead of "address":

// Root cause in the codebase with @> marks to highlight the relevant section
bytes32 private constant MESSAGE_TYPEHASH = keccak256("SnowmanClaim(addres receiver, uint256 amount)"); // @> typo: "addres" should be "address"

Because the typehash is hashed into the digest, any signature produced by standard EIP-712 tooling (ethers.js, wallets, signTypedData) uses the correct type string and therefore produces a different digest. _isValidSignature always fails and claimSnowman reverts with SA__InvalidSignature. The airdrop is only usable through a non-standard flow that fetches the raw digest from getMessageHash().

Risk

Likelihood: High — any user or integrator signing with standard EIP-712 typed-data APIs will hit the revert; only a bespoke frontend that deliberately signs the contract's non-standard digest can claim.

Impact: High — the core claim function is unusable for standard signers, breaking the airdrop for virtually all recipients.

Proof of Concept

// Run with: forge test --match-test testStandardEIP712SignatureAlwaysFails
bytes32 typoTypehash = keccak256("SnowmanClaim(addres receiver, uint256 amount)");
bytes32 correctTypehash = keccak256("SnowmanClaim(address receiver, uint256 amount)");
assertTrue(typoTypehash != correctTypehash);
​
// Digest a standard EIP-712 wallet produces (correct type string)
bytes32 domainSeparator = keccak256(abi.encode(
keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"),
keccak256("Snowman Airdrop"), keccak256("1"), block.chainid, address(airdrop)
));
bytes32 structHash = keccak256(abi.encode(correctTypehash, alice, uint256(1)));
bytes32 standardDigest = keccak256(abi.encodePacked("\x19\x01", domainSeparator, structHash));
​
(uint8 v, bytes32 r, bytes32 s) = vm.sign(alKey, standardDigest);
vm.prank(alice);
snow.approve(address(airdrop), 1);
​
vm.prank(satoshi);
vm.expectRevert(SnowmanAirdrop.SA__InvalidSignature.selector);
airdrop.claimSnowman(alice, AL_PROOF, v, r, s);
// If the typo did not exist, this claim would succeed instead of reverting.

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 2 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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