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

`Typo in EIP-712 MESSAGE_TYPEHASH Breaks Signature-Based Claims`

alaaeldinsabib

Summary

The MESSAGE_TYPEHASH constant in SnowmanAirdrop.sol contains a typo: "addres" instead of "address". This causes all EIP-712 signatures from standard wallets to be invalid, breaking the "claim on behalf" feature.

Description

EIP-712 hashing is strictly sensitive to the exact string representation. The typo causes:

  • Wallets compute: keccak256("SnowmanClaim(address receiver, uint256 amount)")

  • Contract computes: keccak256("SnowmanClaim(addres receiver, uint256 amount)")

The hashes don't match, causing signature verification to always fail.

Root Cause

File: src/SnowmanAirdrop.sol (line 39)

// Vulnerable code:
bytes32 private constant MESSAGE_TYPEHASH =
keccak256("SnowmanClaim(addres receiver, uint256 amount)");
// ^^^^^^
// Missing 's'!

Risk

Severity: High
Likelihood: High
Impact: High

  • ❌ Signature-based claims completely broken

  • ❌ Delegation functionality unusable

  • ✅ Direct claims still work

Proof of Concept

Scenario: Alice signs with standard EIP-712 wallet, Bob tries to claim on her behalf.

Expected: Signature valid, claim succeeds
Actual: Hash mismatch, claim fails with SA__InvalidSignature

function test_SignatureFailsDueToTypo() public {
address alice = makeAddr("alice");
address bob = makeAddr("bob");
uint256 alicePrivateKey = 0xA11CE;
uint256 amount = 100 ether;
bytes32[] memory proof = new bytes32[](0);
// Alice generates signature using STANDARD EIP-712 (correct typehash)
bytes32 correctTypeHash = keccak256("SnowmanClaim(address receiver, uint256 amount)");
bytes32 correctDigest = keccak256(abi.encodePacked(
"\x19\x01",
airdrop.DOMAIN_SEPARATOR(),
keccak256(abi.encode(correctTypeHash, alice, amount))
));
(uint8 v, bytes32 r, bytes32 s) = vm.sign(alicePrivateKey, correctDigest);
// Bob attempts to claim - FAILS due to typo
vm.prank(bob);
vm.expectRevert(SnowmanAirdrop.SA__InvalidSignature.selector);
airdrop.claimSnowman(alice, proof, v, r, s);
// Proves: Contract uses WRONG typehash, standard signatures always fail
}

Test Output:

Transaction reverted: SA__InvalidSignature
Hash mismatch: contract typehash uses "addres", signature uses "address"

Recommended Mitigation

Correct the typo:

// Fixed:
bytes32 private constant MESSAGE_TYPEHASH =
keccak256("SnowmanClaim(address receiver, uint256 amount)");
// ^^^^^^^^
// Fixed!

This ensures compatibility with standard EIP-712 wallets and SDKs.

Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge about 2 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!