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

Typo in MESSAGE_TYPEHASH ("addres" instead of "address") breaks all claimSnowman signature verification

hackinghacked674

Root + Impact

Root: MESSAGE_TYPEHASH in SnowmanAirdrop.sol:49 contains a typo — "addres" instead of "address" — producing an incorrect keccak256 hash.

Impact: All calls to claimSnowman revert with SA__InvalidSignature, making it impossible for anyone (receiver or delegate) to claim Snowman NFTs through the airdrop mechanism.

Description

  • Recipients or delegates are expected to claim Snowman NFTs by calling SnowmanAirdrop::claimSnowman with a valid EIP-712 signature (v, r, s).

  • However, MESSAGE_TYPEHASH is defined with a typo — "addres" instead of "address". This causes getMessageHash() to produce a different digest than what standard EIP-712 tools (MetaMask, ethers.js, viem) generate. As a result, _isValidSignature always fails, and claimSnowman reverts for every user — both direct claimers and delegates.

bytes32 private constant MESSAGE_TYPEHASH = keccak256("SnowmanClaim(@> addres receiver, uint256 amount)");
// "addres" is missing an 's' — should be "address"

Risk

Likelihood:

  • Every call to claimSnowman passes through _isValidSignature, which uses the buggy typehash to compute the digest. This mismatch occurs on every invocation — no special conditions needed.

Impact:

  • No one can claim Snowman NFTs through SnowmanAirdrop::claimSnowman, rendering the airdrop contract completely non-functional.

  • Snow tokens lose their utility — users who purchased or earned Snow tokens cannot exchange them for NFTs, undermining the token economy.

Proof of Concept

The following tests demonstrate that:

  1. The correct and buggy typehashes produce completely different keccak256 values

  2. A signature created with the correct EIP-712 typehash is rejected by claimSnowman

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;
​
import {Test, console2} from "forge-std/Test.sol";
import {Snow} from "../src/Snow.sol";
import {Snowman} from "../src/Snowman.sol";
import {SnowmanAirdrop} from "../src/SnowmanAirdrop.sol";
import {MockWETH} from "../src/mock/MockWETH.sol";
import {Helper} from "../script/Helper.s.sol";
import {MessageHashUtils} from "@openzeppelin/contracts/utils/cryptography/MessageHashUtils.sol";
​
contract PoC_H2_TypehashTypo is Test {
Snow snow;
Snowman nft;
SnowmanAirdrop airdrop;
MockWETH weth;
Helper deployer;
​
bytes32 public ROOT = 0xc0b6787abae0a5066bc2d09eaec944c58119dc18be796e93de5b2bf9f80ea79a;
​
bytes32 alProofA = 0xf99782cec890699d4947528f9884acaca174602bb028a66d0870534acf241c52;
bytes32 alProofB = 0xbc5a8a0aad4a65155abf53bb707aa6d66b11b220ecb672f7832c05613dba82af;
bytes32 alProofC = 0x971653456742d62534a5d7594745c292dda6a75c69c43a6a6249523f26e0cac1;
bytes32[] AL_PROOF = [alProofA, alProofB, alProofC];
​
address alice;
uint256 alKey;
​
// Correct EIP-712 typehash (note: "address" spelled correctly)
bytes32 constant CORRECT_TYPEHASH = keccak256("SnowmanClaim(address receiver, uint256 amount)");
// Buggy typehash used in the contract (note: "addres" — missing 's')
bytes32 constant BUGGY_TYPEHASH = keccak256("SnowmanClaim(addres receiver, uint256 amount)");
​
function setUp() public {
deployer = new Helper();
(airdrop, snow, nft, weth) = deployer.run();
(alice, alKey) = makeAddrAndKey("alice");
}
​
function test_typehashesAreDifferent() public pure {
// Demonstrate that the two typehashes produce completely different values
assert(CORRECT_TYPEHASH != BUGGY_TYPEHASH);
​
console2.log("Correct typehash:");
console2.logBytes32(CORRECT_TYPEHASH);
console2.log("Buggy typehash (in contract):");
console2.logBytes32(BUGGY_TYPEHASH);
}
​
function test_correctSignatureReverts() public {
// ① Setup — alice has Snow tokens and approves airdrop
assertGt(snow.balanceOf(alice), 0, "Alice should have Snow tokens");
vm.prank(alice);
snow.approve(address(airdrop), snow.balanceOf(alice));
​
// ② Create signature using CORRECT EIP-712 typehash (what standard tools would produce)
uint256 amount = snow.balanceOf(alice);
bytes32 correctStructHash = keccak256(
abi.encode(CORRECT_TYPEHASH, alice, amount)
);
​
// Build the EIP-712 domain separator manually to match the contract's domain
bytes32 domainSeparator = keccak256(
abi.encode(
keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"),
keccak256("Snowman Airdrop"),
keccak256("1"),
block.chainid,
address(airdrop)
)
);
bytes32 correctDigest = MessageHashUtils.toTypedDataHash(domainSeparator, correctStructHash);
​
// Alice signs with the correct digest
(uint8 v, bytes32 r, bytes32 s) = vm.sign(alKey, correctDigest);
​
// ③ Verify — claimSnowman reverts because contract uses buggy typehash
vm.prank(alice);
vm.expectRevert(SnowmanAirdrop.SA__InvalidSignature.selector);
airdrop.claimSnowman(alice, AL_PROOF, v, r, s);
​
// Alice still has no NFTs
assertEq(nft.balanceOf(alice), 0, "Alice should still have 0 NFTs");
console2.log("Claim with correct EIP-712 signature: REVERTED (as expected due to typo)");
}
}

Recommended Mitigation

Fix the typo in MESSAGE_TYPEHASH:

- 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 3 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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