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

EIP-712 typehash typo (addres) rejects signatures from spec-compliant signers

dngr2

Description

The EIP-712 type string used to build the claim digest is malformed:

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

addres is a typo for address, and the string also contains spaces that EIP-712 forbids (the canonical encoding is SnowmanClaim(address receiver,uint256 amount)). So the on-chain typehash differs from what any spec-compliant signer (a wallet's signTypedData) computes, and a correctly-produced off-chain signature is rejected by _isValidSignature.

The "claim on behalf of a recipient via v, r, s" feature therefore only works if the signer signs the raw getMessageHash output; it cannot be produced with standard EIP-712 tooling.

Risk

Likelihood: High

  • Every recipient authorizing a delegated claim through a standard EIP-712 wallet is affected.

Impact: Medium

  • The delegated-claim signature feature is broken for compliant signers; intended, valid claims revert.

Proof of Concept

Signing the same claim with the correct EIP-712 type string is rejected (and the malformed one reproduces the contract's own digest, confirming the typehash is the cause):

function test_M1_eip712TypehashTypoRejectsCompliantSig() public {
bytes32 domainSep = keccak256(abi.encode(
keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"),
keccak256(bytes("Snowman Airdrop")), keccak256(bytes("1")), block.chainid, address(airdrop)));
​
bytes32 badStruct = keccak256(abi.encode(keccak256("SnowmanClaim(addres receiver, uint256 amount)"), alice, uint256(1)));
assertEq(keccak256(abi.encodePacked("\x19\x01", domainSep, badStruct)), airdrop.getMessageHash(alice));
​
bytes32 goodStruct = keccak256(abi.encode(keccak256("SnowmanClaim(address receiver,uint256 amount)"), alice, uint256(1)));
(uint8 v, bytes32 r, bytes32 s) = vm.sign(alKey, keccak256(abi.encodePacked("\x19\x01", domainSep, goodStruct)));
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); // compliant signature rejected
}

Recommended Mitigation

Use the canonical EIP-712 type string:

- keccak256("SnowmanClaim(addres receiver, uint256 amount)");
+ keccak256("SnowmanClaim(address receiver,uint256 amount)");
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)"); ```

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