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

Typo in EIP-712 `MESSAGE_TYPEHASH` ("addres" instead of "address") breaks signature compatibility with all standard wallets

404persona

Description

  • The SnowmanAirdrop contract uses EIP-712 typed structured data for signature verification, allowing third parties to claim Snowman NFTs on behalf of recipients. The MESSAGE_TYPEHASH is used to construct the digest that recipients sign.

  • The typehash contains a typo — "addres" instead of "address" — which means the contract's internal digest differs from what any standards-compliant EIP-712 implementation (MetaMask, ethers.js, viem, etc.) would produce. Any signature generated by a standard wallet will be rejected by the contract.

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

Risk

Likelihood:

  • Every standard EIP-712 implementation uses the correct Solidity type names — the mismatch is guaranteed

  • Any frontend or wallet constructing the signing request with "address receiver" produces a different typehash

Impact:

  • All legitimate off-chain signatures from standard wallets are rejected

  • The "claim on behalf of" functionality is completely broken for real-world usage

  • Recipients cannot delegate their claims to gas payers as intended by the protocol design

Proof of Concept

// 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 {Helper} from "../script/Helper.s.sol";
import {MockWETH} from "../src/mock/MockWETH.sol";
​
contract PoC_H01 is Test {
Snow snow;
Snowman nft;
SnowmanAirdrop airdrop;
MockWETH weth;
​
address alice;
uint256 alKey;
​
function setUp() public {
Helper deployer = new Helper();
(airdrop, snow, nft, weth) = deployer.run();
(alice, alKey) = makeAddrAndKey("alice");
}
​
// H-01: EIP-712 MESSAGE_TYPEHASH contains "addres" instead of "address".
// The contract's digest differs from any standard EIP-712 implementation,
// breaking signature compatibility with all real wallets.
function test_H01_TypehashTypo() public {
bytes32 wrongTypehash = keccak256("SnowmanClaim(addres receiver, uint256 amount)");
bytes32 correctTypehash = keccak256("SnowmanClaim(address receiver, uint256 amount)");
​
console2.log("Wrong typehash (in contract):");
console2.logBytes32(wrongTypehash);
console2.log("Correct typehash:");
console2.logBytes32(correctTypehash);
​
assertTrue(wrongTypehash != correctTypehash, "Typehashes should differ due to typo");
​
uint256 amount = snow.balanceOf(alice);
assertEq(amount, 1, "Alice should have 1 Snow token");
​
vm.prank(alice);
snow.approve(address(airdrop), amount);
​
bytes32 contractDigest = airdrop.getMessageHash(alice);
​
console2.log("Contract digest (wrong typehash):");
console2.logBytes32(contractDigest);
console2.log("Any standard EIP-712 tool would produce a DIFFERENT digest,");
console2.log("making legitimate off-chain signatures INVALID");
}
}

Output:

[PASS] test_H01_TypehashTypo() (gas: 70162)
Logs:
Wrong typehash (in contract):
0xff59e96f4a12fdaf4e417a1440b578f822f6cb542be1a2a7c196280bec54f9ab
Correct typehash:
0x6cedfa9a039e959a5fe5a6e4224acac28bb707e70fb8ad28e3ac109c88b280d6
Contract digest (wrong typehash):
0xade7201527deccec00a028e81e6b632f8258d3204971d43e7912ce0010068990
Any standard EIP-712 tool would produce a DIFFERENT digest,
making legitimate off-chain signatures INVALID

Recommended Mitigation

Fix the typo in the MESSAGE_TYPEHASH constant by correcting "addres" to "address". This aligns the contract's EIP-712 type string with the actual Solidity type used in the SnowmanClaim struct, restoring compatibility with all standard wallets and EIP-712 libraries.

- 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 1 hour 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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