AirDropper
AI First Flight #5
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Submission Details
Severity: high
Valid

Deploy.s.sol funds the airdrop from a different USDC address than the one stored in the contract, leaving the contract permanently unfunded

virgilbb

Root + Impact

Description

  • Deploy.s.sol is responsible for deploying MerkleAirdrop and funding it with 100 USDC so eligible users can claim their allocation.

  • The script uses two different USDC addresses. The constructor is passed s_zkSyncUSDC = 0x1D17CbCf0D6d143135be902365d2e5E2a16538d4, which becomes the immutable i_airdropToken the contract sends to claimants. The subsequent transfer call uses the hardcoded address 0x1d17CBcF0D6D143135aE902365D2E5e2A16538D4. These addresses differ at byte 9 (be9... vs ae9...).

// script/Deploy.s.sol
address public s_zkSyncUSDC = 0x1D17CbCf0D6d143135be902365d2e5E2a16538d4;
// ^^^ 'b'
​
function run() public {
vm.startBroadcast();
MerkleAirdrop airdrop = deployMerkleDropper(s_merkleRoot, IERC20(s_zkSyncUSDC));
// @> different address used here — 'a' not 'b' at the same byte
IERC20(0x1d17CBcF0D6D143135aE902365D2E5e2A16538D4).transfer(address(airdrop), s_amountToAirdrop);
// ^^^
vm.stopBroadcast();
}

Risk

Likelihood:

  • The deploy script is the only intended funding mechanism. Every deployment using this script produces an unfunded contract — no special conditions are required.

Impact:

  • MerkleAirdrop is deployed with i_airdropToken pointing to one USDC address but zero balance of that token. Every claim() call reverts with an ERC-20 insufficient balance error. All 4 eligible recipients receive nothing.

  • The mismatch also means 100 USDC is transferred from the wrong address — which would either revert (if that address lacks balance/approval) or silently fund a contract with a token it can never distribute.

Proof of Concept

Compare the two addresses character-by-character:

Constructor: 0x1D17CbCf0D6d143135be902365d2e5E2a16538d4
Transfer: 0x1d17CBcF0D6D143135aE902365D2E5e2A16538D4
^
'b' vs 'a' — different addresses

After deployment, i_airdropToken.balanceOf(address(airdrop)) == 0 and every claim() call fails with ERC-20 transfer error.

Recommended Mitigation

Use the same variable for both the constructor and the transfer call:

function run() public {
vm.startBroadcast();
MerkleAirdrop airdrop = deployMerkleDropper(s_merkleRoot, IERC20(s_zkSyncUSDC));
- IERC20(0x1d17CBcF0D6D143135aE902365D2E5e2A16538D4).transfer(address(airdrop), s_amountToAirdrop);
+ IERC20(s_zkSyncUSDC).transfer(address(airdrop), s_amountToAirdrop);
vm.stopBroadcast();
}
Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge about 3 hours ago
Submission Judgement Published
Validated
Assigned finding tags:

[H-01] Address of USDC token in `Deploy.s.sol` is wrong causing the claiming process to fail

## Description The `s_zkSyncUSDC` address in `Deploy.s.sol` is incorrectly set, leading to a failure in the claiming process. This error results in funds being stuck in the `MerkleAirdrop` contract due to the immutability of the token address. ## Impact All funds become permanently trapped in the `MerkleAirdrop` contract, rendering them inaccessible for claiming or transfer. **Proof of Concept:** To demonstrate the issue, a test contract can be added and executed using the following command: `forge test --zksync --rpc-url $RPC_ZKSYNC --mt testDeployOnZkSync` Use the RPC URL `https://mainnet.era.zksync.io` for testing. <details> <summary>Proof Of Code</summary> ```javascript // SPDX-License-Identifier: MIT pragma solidity 0.8.24; import { MerkleAirdrop, IERC20 } from "../src/MerkleAirdrop.sol"; import { Test, console2 } from "forge-std/Test.sol"; contract MerkleAirdropTest is Test { MerkleAirdrop public s_airdrop; uint256 s_amountToCollect = (25 * 1e6); // 25.000000 address s_collectorOne = 0x20F41376c713072937eb02Be70ee1eD0D639966C; bytes32 s_proofOne = 0x32cee63464b09930b5c3f59f955c86694a4c640a03aa57e6f743d8a3ca5c8838; bytes32 s_proofTwo = 0x8ff683185668cbe035a18fccec4080d7a0331bb1bbc532324f40501de5e8ea5c; bytes32[] s_proof = [s_proofOne, s_proofTwo]; address public deployer; // From Deploy.t.sol bytes32 public s_merkleRoot = 0x3b2e22da63ae414086bec9c9da6b685f790c6fab200c7918f2879f08793d77bd; address public s_zkSyncUSDC = 0x1d17CBcF0D6D143135aE902365D2E5e2A16538D4; uint256 public s_amountToAirdrop = 4 * (25 * 1e6); function setUp() public { deployer = makeAddr("deployer"); deal(0x1D17CbCf0D6d143135be902365d2e5E2a16538d4, deployer, 100 * 1e6); vm.deal(s_collectorOne, 100 ether); } function testDeployOnZkSync() public { if (block.chainid != 324) { return; } vm.startPrank(deployer); // From here there is the code from run() s_airdrop = deployMerkleDropper(s_merkleRoot, IERC20(s_zkSyncUSDC)); // Send USDC -> Merkle Air Dropper IERC20(0x1d17CBcF0D6D143135aE902365D2E5e2A16538D4).transfer(address(s_airdrop), s_amountToAirdrop); // end code from run vm.stopPrank(); vm.startPrank(s_collectorOne); s_airdrop.claim{ value: s_airdrop.getFee() }(s_collectorOne, s_amountToCollect, s_proof); vm.stopPrank(); } function deployMerkleDropper(bytes32 merkleRoot, IERC20 zkSyncUSDC) public returns (MerkleAirdrop) { return (new MerkleAirdrop(merkleRoot, zkSyncUSDC)); } } ``` </details> ## Recommendations To resolve the issue, update the s_zkSyncUSDC address in Deploy.s.sol to the correct value: ```diff - address public s_zkSyncUSDC = 0x1D17CbCf0D6d143135be902365d2e5E2a16538d4; + address public s_zkSyncUSDC = 0x1d17CBcF0D6D143135aE902365D2E5e2A16538D4; ```

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