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

EIP-712 `MESSAGE_TYPEHASH` contains a typo: `"addres"` instead of `"address"`, and includes non-standard spaces

alvap

Root + Impact

Description

The MESSAGE_TYPEHASH constant in SnowmanAirdrop.sol at line 49 has a critical typo in the type string. The word "address" is misspelled as "addres" (missing the second s). Additionally, the EIP-712 type string includes spaces after commas (e.g., "addres receiver, uint256 amount"), which deviates from the EIP-712 specification that uses no spaces (e.g., "SnowmanClaim(address receiver,uint256 amount)").

// SnowmanAirdrop.sol, line 49
bytes32 private constant MESSAGE_TYPEHASH =
keccak256("SnowmanClaim(addres receiver, uint256 amount)");
// ^^^^^^ typo: should be "address"
// ^ space after comma: non-standard EIP-712

The correct EIP-712 typehash should be:

bytes32 private constant MESSAGE_TYPEHASH =
keccak256("SnowmanClaim(address receiver,uint256 amount)");
​
## Risk
​
**Likelihood**:
​
* Reason 1 // Describe WHEN this will occur (avoid using "if" statements)
​
* Reason 2
​
**Impact**:
​
The EIP-712 digest generated by `getMessageHash` uses this incorrect typehash. Any off-chain signer (e.g., a wallet or dApp) that constructs the EIP-712 struct hash using the *correct* EIP-712 type string (`"SnowmanClaim(address receiver,uint256 amount)"`) will produce a different digest than the contract expects. This means legitimate claim signatures generated through standard EIP-712 tooling will be rejected by the contract. The only way to produce a valid signature is to replicate the exact typo off-chain, which is fragile and non-standard.
​
## Proof of Concept
​
A standard EIP-712 signer using the correct type string would produce a different typehash:

keccak256("SnowmanClaim(address receiver,uint256 amount)") != keccak256("SnowmanClaim(addres receiver, uint256 amount)")

​
Any wallet that signs with the correct spelling will produce a signature that the contract rejects with `SA__InvalidSignature()`.
​
## Recommended Mitigation
​
Fix the typo and remove the non-standard space:
​
```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 8 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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