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

EIP-712 MESSAGE_TYPEHASH contains typo 'addres' — standard wallet signatures always fail, third-party claim permanently broken

fishyyh

EIP-712 MESSAGE_TYPEHASH contains typo 'addres' — standard wallet signatures always fail

Impact

High Impact

Likelihood

High Likelihood

Root + Impact

Description

  • SnowmanAirdrop.claimSnowman uses EIP-712 to allow a third party to claim on behalf of a receiver by providing a valid signature from receiver.

  • The MESSAGE_TYPEHASH string is "SnowmanClaim(addres receiver, uint256 amount)" — addres is missing the trailing s, and there is an extra space before uint256. EIP-712 requires "SnowmanClaim(address receiver,uint256 amount)" (correct spelling, no spaces). Every signature produced by MetaMask, ethers.js signTypedData, or any standards-compliant tool will produce a hash that never matches the contract's tryRecover result.

// src/SnowmanAirdrop.sol
@> bytes32 private constant MESSAGE_TYPEHASH =
@> keccak256("SnowmanClaim(addres receiver, uint256 amount)");
// ^^^^^^ missing 's'; extra space before uint256

Risk

Likelihood:

  • Every external caller using a standards-compliant signing library hits this bug unconditionally.

  • The only workaround requires a custom non-standard backend incompatible with all wallets.

Impact:

  • The third-party claim path is entirely non-functional; SA__InvalidSignature is always reverted.

  • EIP-712 domain separation guarantees are violated.

Proof of Concept

bytes32 STANDARD_TYPEHASH = keccak256("SnowmanClaim(address receiver,uint256 amount)");
bytes32 digest = keccak256(abi.encodePacked(hex"1901", domainSeparator,
keccak256(abi.encode(STANDARD_TYPEHASH, alice, amount))));
(uint8 v, bytes32 r, bytes32 s) = vm.sign(aliceKey, digest);
vm.expectRevert(SnowmanAirdrop.SA__InvalidSignature.selector);
airdrop.claimSnowman(alice, proof, v, r, s); // always reverts

Recommended Mitigation

bytes32 private constant MESSAGE_TYPEHASH =
- keccak256("SnowmanClaim(addres receiver, uint256 amount)");
+ keccak256("SnowmanClaim(address receiver,uint256 amount)");

Also consider adding nonce and deadline fields to prevent signature replay.

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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