AirDropper

[HIGH-1] Fee Denomination Mismatch — FEE Constant Is 1e9 Wei, Not 1e9 ETH

File: src/MerkleAirdrop.sol (line 18), script/Deploy.s.sol

Summary

The contract defines FEE = 1e9 with no unit annotation. In Solidity, numeric literals in wei mean FEE = 1 Gwei = 0.000000001 ETH. The README states the fee is required for cost recovery, yet this fee is economically negligible (fractions of a cent), effectively meaning claims are free, and the fee mechanism provides no protection or revenue.

Vulnerability Details

In Solidity, all values are in wei unless explicitly denoted with ether or gwei. 1e9 = 1,000,000,000 wei = 1 Gwei ≈ $0.000000003 at ETH=$3000.

If the intent was 1e9 ETH (i.e., 1e9 * 1e18 wei), the constant is off by 18 orders of magnitude. Alternatively, if the intent is to charge a $0.01 fee, the value should be calibrated against current gas/ETH pricing dynamically.

This also makes the fee mechanism inconsistent on zkSync where gas pricing differs from mainnet.

Impact

• The fee provides essentially zero economic protection against spam claiming.

• CRITICAL-1 (unlimited re-claiming) is made even easier because the attacker fee cost is negligible.

• No meaningful revenue for the protocol owner.

Tools Used

• Manual analysis

• Unit analysis

Recommendations

If fee in ETH is intended:

Alternatively, make the fee configurable by the owner: