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

Malformed EIP-712 type string in MESSAGE_TYPEHASH breaks standard signature tooling

aclod
# [L-1] Malformed EIP-712 type string in `MESSAGE_TYPEHASH` breaks standard signature tooling
​
## Summary
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`SnowmanAirdrop` is meant to let a third party claim on a recipient's behalf using the recipient's EIP-712 signature. However, the `MESSAGE_TYPEHASH` is built from a malformed type string: it contains a typo (`addres`) and spaces that violate the EIP-712 `encodeType` specification. As a result, any signature produced with standard EIP-712 tooling (e.g. wallets calling `eth_signTypedData_v4` with the correct type) will not verify, breaking the intended "claim on behalf" feature.
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## Vulnerability Details
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```solidity
bytes32 private constant MESSAGE_TYPEHASH =
keccak256("SnowmanClaim(addres receiver, uint256 amount)");
```
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Two problems:
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1. **Typo**: `addres` instead of `address`.
2. **Invalid EIP-712 formatting**: per EIP-712, the `encodeType` string must contain no spaces — the canonical form is `"SnowmanClaim(address receiver,uint256 amount)"`. The code includes a space after the comma and uses the wrong type name.
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Because `getMessageHash` derives the digest from this incorrect typehash, the digest the contract expects does not match the digest a standards-compliant signer (MetaMask, ethers, viem `signTypedData`) computes for `SnowmanClaim(address receiver,uint256 amount)`. Signatures created the standard way therefore fail `_isValidSignature`, and the recipient cannot have a third party claim on their behalf.
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## Impact
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- The "claim on behalf via signature" feature is effectively unusable with standard wallet/library tooling.
- Integrations relying on EIP-712 compliance will silently produce signatures that always revert with `SA__InvalidSignature`.
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Functionality is broken rather than funds being stolen, so this is **Low** severity.
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## Recommended Mitigation
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Use the canonical, correctly spelled EIP-712 type string:
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```diff
- 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 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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