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

EIP-712 MESSAGE_TYPEHASH contains a typo (addres) that causes signature verification to always fail, permanently breaking claimSnowman()

cybervikink

Root + Impact

Description

SnowmanAirdrop uses EIP-712 typed structured data to allow a third party to claim on behalf of a receiver. The receiver signs a SnowmanClaim struct off-chain, and the contract verifies the signature via _isValidSignature() → getMessageHash().

getMessageHash() hashes the struct using MESSAGE_TYPEHASH. For EIP-712 to work correctly, the type string used to compute the typehash must match the canonical Solidity struct type signature exactly.

// @> Typo: "addres" instead of "address" — one character missing
bytes32 private constant MESSAGE_TYPEHASH =
keccak256("SnowmanClaim(addres receiver, uint256 amount)");

Risk

Likelihood:

  • This occurs on every single call to claimSnowman() without exception, as the typehash is a compile-time constant that cannot be corrected post-deployment.

  • Any legitimate receiver who signs the message with a proper EIP-712 wallet will have their claim rejected.

Impact:

  • The entire airdrop mechanism is permanently bricked at deployment — no Snowman NFT can ever be claimed through claimSnowman().

  • All Snow tokens that users hold for the purpose of claiming NFTs become useless for that purpose.

  • The protocol's core purpose (distributing Snowman NFTs via the airdrop) is completely non-functional.

Proof of Concept

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;
​
import {Test} from "forge-std/Test.sol";
import {SnowmanAirdrop} from "../src/SnowmanAirdrop.sol";
import {Snow} from "../src/Snow.sol";
import {Snowman} from "../src/Snowman.sol";
import {Helper} from "../script/Helper.s.sol";
​
contract TypehashTypoPoC is Test {
// The correct typehash (what signers will produce)
bytes32 constant CORRECT_TYPEHASH =
keccak256("SnowmanClaim(address receiver,uint256 amount)");
​
// The broken typehash (what the contract actually uses)
bytes32 constant BROKEN_TYPEHASH =
keccak256("SnowmanClaim(addres receiver, uint256 amount)");
​
function testTypehashMismatch() public pure {
// They are different — signatures will never verify
assert(CORRECT_TYPEHASH != BROKEN_TYPEHASH);
}
​
function testClaimAlwaysRevertsOnSignature() public {
Helper helper = new Helper();
(SnowmanAirdrop airdrop, Snow snow,,) = helper.run();
​
address alice = makeAddr("alice");
// Give alice a Snow balance so balance check passes
// (She already earned 1 from Helper)
​
// Create a valid EIP-712 signature using the CORRECT typehash
uint256 alicePk = 0xA11CE;
address signer = vm.addr(alicePk);
deal(address(snow), signer, 1);
​
// Sign using the correct type string
bytes32 correctDigest = keccak256(
abi.encodePacked(
"\x19\x01",
airdrop.DOMAIN_SEPARATOR(), // hypothetical getter
keccak256(abi.encode(CORRECT_TYPEHASH, signer, uint256(1)))
)
);
(uint8 v, bytes32 r, bytes32 s) = vm.sign(alicePk, correctDigest);
​
bytes32[] memory proof = new bytes32[](0);
​
// This ALWAYS reverts with SA__InvalidSignature because the contract
// hashes with the broken typehash, producing a different digest
vm.expectRevert(SnowmanAirdrop.SA__InvalidSignature.selector);
airdrop.claimSnowman(signer, proof, v, r, s);
}
}

Recommended Mitigation

Fix the type string to exactly match the Solidity struct definition. Note also that EIP-712 canonical type strings do not include spaces after commas:

// Before (broken):
bytes32 private constant MESSAGE_TYPEHASH =
keccak256("SnowmanClaim(addres receiver, uint256 amount)");
​
// After (correct):
bytes32 private constant MESSAGE_TYPEHASH =
keccak256("SnowmanClaim(address receiver,uint256 amount)");
Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge about 6 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)"); ```

Support

FAQs

Can't find an answer? Chat with us on Discord, Twitter or Linkedin.

Give us feedback!