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

Incorrect MESSAGE_TYPEHASH Causes Signature Verification Failure

muzammilmohammed678

Root + Impact

Description

  • Describe the normal behavior in one or more sentences
    The `MESSAGE_TYPEHASH` constant contains a typo: `"addres"` instead of `"address"`. This causes EIP-712 signature verification to fail because the typehash doesn't match the actual struct definition, breaking the entire claim mechanism.

  • Explain the specific issue or problem in one or more sentences
    The typehash is used for EIP-712 compliant message signing. The typo means the hash will never match the actual struct being encoded, causing all signature verifications to fail.

The typehash is used for EIP-712 compliant message signing. The typo means the hash will never match the actual struct being encoded, causing all signature verifications to fail.
​
```solidity
// @> SnowmanAirdrop.sol:49
bytes32 private constant MESSAGE_TYPEHASH = keccak256("SnowmanClaim(addres receiver, uint256 amount)");
// ^^^^^^ Should be "address"
```
​
When `_hashTypedDataV4()` is called with this typehash, it will produce a different hash than what users sign, causing `_isValidSignature()` to always return false.
​
```solidity
// @> SnowmanAirdrop.sol:119-121
return _hashTypedDataV4(
keccak256(abi.encode(MESSAGE_TYPEHASH, SnowmanClaim({receiver: receiver, amount: amount})))
);
```

Risk

Likelihood:

  • * The typo exists in the deployed code

    * Every signature verification will fail due to the incorrect typehash

    * This affects 100% of claim attempts

    * No workaround exists without fixing the contract

Impact:

  • * Complete failure of the airdrop claim mechanism

    * Users cannot claim their Snowman NFTs

    * All signed messages will be rejected

    * Contract becomes unusable for its intended purpose

Proof of Concept

```solidity
function testIncorrectTypehash() public {
SnowmanAirdrop airdrop = deployAirdrop();
address user = makeAddr("user");
(uint8 v, bytes32 r, bytes32 s) = getValidSignature(user);
// This will always fail because the typehash is wrong
vm.prank(user);
snow.approve(address(airdrop), 1);
vm.expectRevert(SA__InvalidSignature.selector);
airdrop.claimSnowman(user, validProof, v, r, s);
// The signature is actually valid, but typehash mismatch causes failure
}
```
​

Recommended Mitigation

```diff
// SnowmanAirdrop.sol
​
- 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 17 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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