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

MESSAGE_TYPEHASH contains typo 'addres' instead of 'address' — EIP-712 signatures permanently broken

squashingbugsforlife

Root + Impact

Description

  • Normal behavior: EIP-712 requires the type hash to exactly match the struct definition. MESSAGE_TYPEHASH should encode SnowmanClaim(address receiver, uint256 amount).

  • The issue: Line 49 of SnowmanAirdrop.sol contains a critical typo — addres instead of address. Every signature generated off-chain using the correct type string hashes to a different digest than what the contract computes, causing _isValidSignature() to always return false. The airdrop is completely non-functional from deployment.

```solidity
// src/SnowmanAirdrop.sol#49
// @> TYPO: 'addres' instead of 'address'
bytes32 private constant MESSAGE_TYPEHASH =
keccak256("SnowmanClaim(addres receiver, uint256 amount)");
// ^^^^^^ missing 's'
```

Risk

Likelihood:

  • This is a compile-time constant. The typo is baked into the contract permanently at deployment with a 100% failure rate on every signature verification call.

  • Every single user attempting to claim via signature receives SA__InvalidSignature with no workaround available.

Impact:

  • The entire airdrop signature mechanism is broken, no user can claim via signature.

  • The contract cannot be fixed without redeployment, all deployed instances are permanently broken.

Proof of Concept

The following Foundry test proves that off-chain and on-chain type hashes diverge due to the typo. Both hashes are computed and asserted unequal, confirming that any signature generated by standard EIP-712 tooling will never match what the contract verifies. claimSnowman() always reverts with SA__InvalidSignature for every user.

​
```solidity
function testTypehashMismatch() public {
bytes32 correctHash = keccak256(
"SnowmanClaim(address receiver, uint256 amount)"
);
bytes32 buggyHash = keccak256(
"SnowmanClaim(addres receiver, uint256 amount)"
);
​
// Hashes are not equal — signatures will never verify
assertNotEq(correctHash, buggyHash);
​
vm.expectRevert(SnowmanAirdrop.SA__InvalidSignature.selector);
airdrop.claimSnowman(receiver, merkleProof, v, r, s);
}
```

Recommended Mitigation

The fix is a single character correction to the type string constant. Because MESSAGE_TYPEHASH is immutable at deployment, the contract must be redeployed. No other changes are required, the corrected hash automatically aligns with signatures generated by any standard EIP-712 compliant wallet or library. A regression test verifying the hash on every deployment is strongly recommended.

```diff
- bytes32 private constant MESSAGE_TYPEHASH =
- keccak256("SnowmanClaim(addres receiver, uint256 amount)");
+ bytes32 private constant MESSAGE_TYPEHASH =
+ keccak256("SnowmanClaim(address receiver, uint256 amount)");
​
+ // Regression test — add to test suite:
+ function testTypehashCorrect() public {
+ bytes32 expected = keccak256("SnowmanClaim(address receiver, uint256 amount)");
+ assertEq(airdrop.MESSAGE_TYPEHASH(), expected);
+ }
```
Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge about 7 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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