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

EIP-712 MESSAGE_TYPEHASH Typo Breaks Signature Verification

zanyjoy408

Description

  • The SnowmanAirdrop contract uses EIP-712 typed data signing to verify that the receiver has authorized the claim. This requires the contract's typehash to match exactly what the user signs.

  • The MESSAGE_TYPEHASH constant contains a typo: "addres" instead of "address". This causes a mismatch between what users sign (using the correct "address" type) and what the contract expects, making all legitimate signatures invalid.

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

Risk

Likelihood:

  • Every legitimate user attempting to claim their airdrop will have their signature rejected

  • Standard EIP-712 signing tools and wallets will generate signatures using the correct "address" type, which will never match the contract's malformed typehash

Impact:

  • Complete denial of service for the airdrop - no legitimate user can claim their Snowman NFTs

  • All Snow tokens locked in users' wallets cannot be exchanged for NFTs through legitimate means

  • Users may be forced to find alternative (potentially exploitative) ways to interact with the contract

Proof of Concept

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;
​
import {Test, console2} from "forge-std/Test.sol";
​
contract TypehashMismatchPoC is Test {
// What the contract has (incorrect)
bytes32 constant WRONG_TYPEHASH = keccak256("SnowmanClaim(addres receiver, uint256 amount)");
​
// What EIP-712 compliant signers will use (correct)
bytes32 constant CORRECT_TYPEHASH = keccak256("SnowmanClaim(address receiver, uint256 amount)");
​
function testTypehashMismatch() public {
console2.log("Wrong typehash (contract): ");
console2.logBytes32(WRONG_TYPEHASH);
​
console2.log("Correct typehash (signers): ");
console2.logBytes32(CORRECT_TYPEHASH);
​
// These will never match
assertFalse(WRONG_TYPEHASH == CORRECT_TYPEHASH);
​
// Output:
// Wrong typehash: 0x...different hash
// Correct typehash: 0x...different hash
}
}

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 2 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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