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

Typo in MESSAGE_TYPEHASH Causes Complete Signature Verification Failure

chefjay

Typo in MESSAGE_TYPEHASH Causes Complete Signature Verification Failure

Description

The MESSAGE_TYPEHASH contains a typo: "addres" instead of "address". This causes all signature verifications to fail because the hash won't match what users sign.

@> bytes32 private constant MESSAGE_TYPEHASH = keccak256("SnowmanClaim(addres receiver, uint256 amount)");
// ^^^^^^^ TYPO!

Risk

Likelihood:

  • The issue is a constant until changed

Impact:

  • NO USER CAN EVER CLAIM AIRDROPS - All signature verifications will fail

  • The entire airdrop mechanism is non-functional

  • Protocol is completely broken

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 {MockWETH} from "../src/mock/MockWETH.sol";
import {IERC20} from "@openzeppelin/contracts/token/ERC20/IERC20.sol";
​
/**
* @title Snowman Audit Tests
* @notice Comprehensive tests proving each vulnerability found in the audit
* @dev Run with: forge test --match-contract SnowmanAuditTests -vvvv
*/
contract SnowmanAuditTests is Test {
Snow public snow;
Snowman public snowman;
SnowmanAirdrop public airdrop;
MockWETH public weth;
​
address public owner = makeAddr("owner");
address public collector = makeAddr("collector");
address public alice = makeAddr("alice");
address public bob = makeAddr("bob");
address public attacker = makeAddr("attacker");
​
uint256 constant BUY_FEE = 0.001 ether;
uint256 constant INITIAL_BALANCE = 1000 ether;
string constant SVG_URI =
"data:image/svg+xml;base64,PHN2ZyB3aWR0aD0iMTAwIiBoZWlnaHQ9IjEwMCI+";
​
bytes32 public merkleRoot;
​
function setUp() public {
// Deploy contracts
vm.startPrank(owner);
weth = new MockWETH();
snow = new Snow(address(weth), BUY_FEE, collector);
snowman = new Snowman(SVG_URI);
​
// Create simple merkle root (not important for most tests)
merkleRoot = keccak256(abi.encodePacked("test"));
airdrop = new SnowmanAirdrop(
merkleRoot,
address(snow),
address(snowman)
);
vm.stopPrank();
​
// Fund test accounts
vm.deal(alice, INITIAL_BALANCE);
vm.deal(bob, INITIAL_BALANCE);
vm.deal(attacker, INITIAL_BALANCE);
​
// Mint WETH to users
weth.mint(alice, INITIAL_BALANCE);
weth.mint(bob, INITIAL_BALANCE);
weth.mint(attacker, INITIAL_BALANCE);
}
/**
* @notice C-2: Typo in MESSAGE_TYPEHASH Causes Signature Verification Failure
* @dev Proves that the signature verification will always fail due to typo
*/
function test_C2_TypeHashTypoCausesSignatureFailure() public {
console2.log("=== C-2: Testing MESSAGE_TYPEHASH Typo ===");
​
// Give alice some Snow tokens
vm.prank(alice);
snow.earnSnow();
​
uint256 aliceBalance = snow.balanceOf(alice);
console2.log(
string(
abi.encodePacked(
"Alice Snow balance:",
vm.toString(aliceBalance)
)
)
);
​
// Create the CORRECT typehash (what user would sign)
bytes32 correctTypeHash = keccak256(
"SnowmanClaim(address receiver, uint256 amount)"
);
console2.log("Correct TypeHash:");
console2.logBytes32(correctTypeHash);
​
// The INCORRECT typehash in contract (with typo "addres")
bytes32 contractTypeHash = keccak256(
"SnowmanClaim(addres receiver, uint256 amount)"
);
console2.log("Contract TypeHash (with typo):");
console2.logBytes32(contractTypeHash);
​
// Proof: The hashes are different
assertFalse(
correctTypeHash == contractTypeHash,
"TypeHashes should be different"
);
​
console2.log(
"VULNERABILITY CONFIRMED: TypeHash mismatch will cause all signature verifications to fail!"
);
}
​
}

Recommended Mitigation

- 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 19 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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