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

SnowmanAirdrop::MESSAGE_TYPEHASH contains a typo ("addres"), so valid EIP-712 signatures from standard wallets are rejected

second_opinion

Root + Impact

Description

  • claimSnowman verifies an EIP-712 signature over SnowmanClaim(receiver, amount), and the digest is built from MESSAGE_TYPEHASH.

  • The type string in the contract is "SnowmanClaim(addres receiver, uint256 amount)", with the typo addres and a space after the comma. The standard type string is SnowmanClaim(address receiver,uint256 amount), so a wallet or library that builds the digest from the real struct (eth_signTypedData_v4, ethers, viem) gets a different digest, _isValidSignature fails and claimSnowman reverts with SA__InvalidSignature.

// src/SnowmanAirdrop.sol
bytes32 private constant MESSAGE_TYPEHASH = keccak256("SnowmanClaim(addres receiver, uint256 amount)"); // @> typo "addres" and a space after the comma, this is not the EIP-712 type string// Root cause in the codebase with @> marks to highlight the relevant section

Risk

Likelihood:

  • Every user who signs through a standard EIP-712 flow is affected, because the typo is in the only type hash the contract accepts.

  • The project own tests sign the digest returned by getMessageHash, so they do not detect the problem.

Impact:

  • Claims by signature, including the delegated claim by a third party, cannot be completed by normal wallet users, which blocks the intended claim flow.

  • Users would have to sign a raw digest produced by the contract, which wallets warn against or do not support.

Proof of Concept

The test builds the digest with the correct EIP-712 type string, signs it with Alice key and calls claimSnowman. This digest differs from getMessageHash(alice) and the claim reverts with SA__InvalidSignature. The test passes on the unmodified code.

function test_H4_typehashTypoRejectsStandardSignature() public {
vm.prank(alice);
snow.approve(address(airdrop), 1);
​
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 correctTypehash = keccak256("SnowmanClaim(address receiver,uint256 amount)");
bytes32 structHash = keccak256(abi.encode(correctTypehash, alice, uint256(1)));
bytes32 standardDigest = keccak256(abi.encodePacked("\x19\x01", domainSeparator, structHash));
​
assertTrue(standardDigest != airdrop.getMessageHash(alice));
​
(uint8 v, bytes32 r, bytes32 s) = vm.sign(alKey, standardDigest);
vm.expectRevert(SnowmanAirdrop.SA__InvalidSignature.selector);
airdrop.claimSnowman(alice, AL_PROOF, v, r, s);
}
// Result: PASS

Recommended Mitigation

Fix the type string and add a test that signs with an independent EIP-712 implementation instead of the contract own helper.

- bytes32 private constant MESSAGE_TYPEHASH = keccak256("SnowmanClaim(addres receiver, uint256 amount)");
+ bytes32 private constant MESSAGE_TYPEHASH = keccak256("SnowmanClaim(address receiver,uint256 amount)");- remove this code
+ add this code
Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge about 1 hour 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!