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

EIP-712 typehash typo ("addres" + extra space) breaks signature verification for any standards-compliant signer

cloebaxter4

Root + Impact

Description

  • The protocol uses EIP-712 typed data signing so wallets, frontends and other contracts can recover signatures over the SnowmanClaim struct in a standardised way.

  • MESSAGE_TYPEHASH contains a typo (addres instead of address) and an extra space, so the digest produced by this contract does not match the EIP-712 type encoding for SnowmanClaim(address receiver,uint256 amount). Any wallet or off-chain signer that hashes the struct correctly per EIP-712 produces a digest the contract rejects.

// src/SnowmanAirdrop.sol
@> bytes32 private constant MESSAGE_TYPEHASH =
@> keccak256("SnowmanClaim(addres receiver, uint256 amount)"); // @> typo + spacing

Risk

Likelihood:

  • Triggers for every signer who uses a standards-compliant EIP-712 signing path (MetaMask signTypedData_v4, ethers _signTypedData, viem, OZ's EIP712.sol, etc.).

  • The contract enforces its broken typehash on every claimSnowman() call.

Impact:

  • Recipients who sign with any standard wallet or library cannot claim — their signatures fail _isValidSignature, blocking the airdrop for non-custom signers.

  • Forces all integrators to hand-craft the malformed type string, breaking interoperability and risking phishing/UX issues (signed payload no longer human-readable as the documented struct).

Proof of Concept

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;
​
import {Test, console2} from "forge-std/Test.sol";
​
contract PoC_TypehashTypo is Test {
function test_typehash_diverges_from_eip712() public pure {
bytes32 correct = keccak256("SnowmanClaim(address receiver,uint256 amount)");
bytes32 contract_ = keccak256("SnowmanClaim(addres receiver, uint256 amount)");
assertTrue(correct != contract_);
}
}

forge test --match-contract PoC_TypehashTypo -vv → [PASS] (the two hashes differ).

Recommended Mitigation

Fix the type string so it matches the EIP-712 spec exactly: spell address, drop the extra space after the comma. The hash will then equal the digest produced by any standards-compliant signer, restoring interoperability with MetaMask, ethers, viem, etc.

- 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 9 days 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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