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

H-02 EIP-712 Typo in MESSAGE_TYPEHASH Breaks All Signature Verifications

mnusurov

Root + Impact

Description

  • Normal behavior: The MESSAGE_TYPEHASH should define the EIP-712 type hash as "SnowmanClaim(address receiver, uint256 amount)" so that signature digests match what users sign off-chain.

  • Issue: The constant contains a typo — "addres" instead of "address" — causing every getMessageHash() and signature verification to compute a wrong digest. As a result, no user can ever successfully claim their airdrop NFT.

// src/SnowmanAirdrop.sol:49
@> bytes32 private constant MESSAGE_TYPEHASH = keccak256("SnowmanClaim(addres receiver, uint256 amount)");
// ^^^^^^ typo: should be "address"

Risk

Likelihood:

  • The typo is in a constant — it affects 100% of claims from day one

  • Every call to getMessageHash() and _hashTypedDataV4() uses the wrong type string

Impact:

  • Every claimSnowman() call reverts with SA__InvalidSignature — the entire airdrop is permanently unusable

  • All legitimate users are blocked from claiming their rightful NFTs

  • The protocol cannot recover without a contract upgrade or redeploy

Proof of Concept

This POC demonstrates that signature verification always fails due to the EIP-712 typo, making the entire airdrop permanently broken.

// From test/audit/HIGH-002-eip712-typo.t.sol
function testExploitVulnerability() public {
// Alice approves tokens for airdrop
vm.prank(alice);
snow.approve(address(airdrop), 1);
​
// Get digest from contract (uses buggy MESSAGE_TYPEHASH with "addres")
bytes32 digest = airdrop.getMessageHash(alice);
​
// Alice signs the digest
(uint8 v, bytes32 r, bytes32 s) = vm.sign(alKey, digest);
​
// Attempt to claim - fails with InvalidSignature
// because digest uses wrong type hash
vm.prank(alice);
vm.expectRevert(SnowmanAirdrop.SA__InvalidSignature.selector);
airdrop.claimSnowman(alice, AL_PROOF, v, r, s);
}
​
function testValidateImpact() public {
// Alice tries to claim
vm.prank(alice);
snow.approve(address(airdrop), 1);
bytes32 digest = airdrop.getMessageHash(alice);
(uint8 v, bytes32 r, bytes32 s) = vm.sign(alKey, digest);
vm.prank(alice);
vm.expectRevert(SnowmanAirdrop.SA__InvalidSignature.selector);
airdrop.claimSnowman(alice, AL_PROOF, v, r, s);
​
// Verify no NFT was minted
assertEq(nft.balanceOf(alice), 0);
​
console2.log("Impact validated: Entire airdrop permanently broken");
}

Recommended Mitigation

Fix the typo in MESSAGE_TYPEHASH by replacing "addres" with "address".

// src/SnowmanAirdrop.sol:49
- 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 8 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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