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

MESSAGE_TYPEHASH contains typo "addres" instead of "address", breaking EIP-712 compatibility with standard signing tools

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Root + Impact

Description

  • Describe the normal behavior in one or more sentences

  • Explain the specific issue or problem in one or more sentences

The `MESSAGE_TYPEHASH` constant uses the misspelled type string `"SnowmanClaim(addres receiver, uint256 amount)"` — missing the final `s` in `address`. EIP-712 requires the type string to exactly match the
canonical Solidity ABI type name. Any off-chain signer using standard EIP-712 libraries (MetaMask `eth_signTypedData`, ethers.js `signTypedData`) will compute a different hash and produce a signature that
always fails on-chain.
​
```solidity
// @> Typo: "addres" should be "address"
bytes32 private constant MESSAGE_TYPEHASH =
keccak256("SnowmanClaim(addres receiver, uint256 amount)");
```
​
### Risk
​
**Likelihood:**
​
- Any integration that constructs the EIP-712 typed data independently using the correct type name `"address"` will produce non-matching signatures
- Only users who call `getMessageHash()` directly on the contract and sign the raw returned bytes32 can successfully claim
​
**Impact:**
​
- Standard wallet integrations and front-ends using EIP-712 typed data signing will always revert with `SA__InvalidSignature`
- The delegated claim flow (having someone else claim on behalf of a recipient) is broken for all standard tooling

Risk

Likelihood:

  • Reason 1 // Describe WHEN this will occur (avoid using "if" statements)

  • Reason 2

Impact:

  • Impact 1

  • Impact 2

Proof of Concept

function test_poc_TypoHash() public {
// Correct EIP-712 typehash (what standard tools compute)
bytes32 correctTypehash = keccak256(
"SnowmanClaim(address receiver, uint256 amount)"
);
​
// What the contract actually uses (with typo)
bytes32 brokenTypehash = keccak256(
"SnowmanClaim(addres receiver, uint256 amount)"
);
​
// They are different — any standard tool will use correctTypehash
assertNotEq(correctTypehash, brokenTypehash);
​
// Alice tries to sign with the CORRECT EIP-712 type string
uint256 amount = snow.balanceOf(alice);
bytes32 structHash = keccak256(abi.encode(correctTypehash, alice, amount));
bytes32 domainSeparator = airdrop.DOMAIN_SEPARATOR();
bytes32 correctDigest = keccak256(
abi.encodePacked("\x19\x01", domainSeparator, structHash)
);
(uint8 v, bytes32 r, bytes32 s) = vm.sign(alKey, correctDigest);
​
// Claim fails — contract uses broken typehash, digest mismatch
vm.prank(alice);
snow.approve(address(airdrop), amount);
vm.expectRevert(SnowmanAirdrop.SA__InvalidSignature.selector);
airdrop.claimSnowman(alice, AL_PROOF, v, r, s);
}

Recommended Mitigation

```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 4 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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