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

EIP-712 MESSAGE_TYPEHASH string is malformed (typo + spacing), breaking standard wallet signing

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Root + Impact

Description

  • A correct EIP-712 typehash must exactly match the encodeType string a compliant signer (MetaMask, ethers.js, viem) auto-generates for the struct: "SnowmanClaim(address receiver,uint256 amount)" — no typos, no spaces after commas.

  • The contract hardcodes a different, malformed string: "addres" instead of "address", plus a stray space after the comma.

bytes32 private constant MESSAGE_TYPEHASH =
keccak256("SnowmanClaim(addres receiver, uint256 amount)");
// @> "addres" typo + space after comma — does not match the EIP-712 spec's encodeType format

Risk

Likelihood:

  • Occurs for every receiver who signs the claim message using any standards-compliant EIP-712 signer, since those tools construct the type string programmatically from the struct definition and will never reproduce this exact typo.


Impact:

  • A signature produced by a standard wallet/library resolves to a completely different digest than the one getMessageHash/_isValidSignature computes on-chain.

  • _isValidSignature will recover the wrong signer and claimSnowman reverts with SA__InvalidSignature for essentially every real-world integration, unless the signer manually hand-crafts the malformed type string (defeating the point of EIP-712 tooling support).

Proof of Concept

-I computed both hashes directly to confirm they diverge (not just visually different strings — genuinely different typehash):

contract's (buggy) typehash : 0xff59e96f4a12fdaf4e417a1440b578f822f6cb542be1a2a7c196280bec54f9a
spec-correct typehash : 0x8cc878fcc8a56748c223ca472f543dc59c856aca7a2e59b34d1c2b4ef288044
+ // What ethers.js/viem/MetaMask auto-generate for struct SnowmanClaim{address receiver; uint256 amount;}:
+ "SnowmanClaim(address receiver,uint256 amount)"
+ // keccak256 -> 0x8cc878fc...044
​
+ // What the contract actually hardcodes and checks against:
+ "SnowmanClaim(addres receiver, uint256 amount)"
+ // keccak256 -> 0xff59e96f...f9a
​
+ // => digest computed by standard tooling != digest the contract expects
+ // => _isValidSignature() recovers the wrong signer => reverts SA__InvalidSignature

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 3 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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