The audit makes no statements or warranties about utility of the code, safety of the code, suitability of the business model, investment advice, endorsement of the platform or its products, regulatory regime for the business model, or any other statements about fitness of the contracts to purpose, or their bug free status. The audit documentation is for discussion purposes only. The information presented in this report is confidential and privileged. If you are reading this report, you agree to keep it confidential, not to copy, disclose or disseminate without the agreement of the Client. If you are not the intended recipient(s) of this document, please note that any disclosure, copying or dissemination of its content is strictly forbidden.
A group of auditors are involved in the work on the audit. The security engineers check the provided source code independently of each other in accordance with the methodology described below:
- Project documentation review.
- General code review.
- Reverse research and study of the project architecture on the source code alone.
- Build an independent view of the project's architecture.
- Identifying logical flaws.
- Manual code check for vulnerabilities listed on the Contractor's internal checklist. The Contractor's checklist is constantly updated based on the analysis of hacks, research, and audit of the clients' codes.
- Code check with the use of static analyzers (i.e Slither, Mythril, etc).
Eliminate typical vulnerabilities (e.g. reentrancy, gas limit, flash loan attacks etc.).
- Detailed study of the project documentation.
- Examination of contracts tests.
- Examination of comments in code.
- Comparison of the desired model obtained during the study with the reversed view obtained during the blind audit.
- Exploits PoC development with the use of such programs as Brownie and Hardhat.
Detect inconsistencies with the desired model.
- Cross check: each auditor reviews the reports of the others.
- Discussion of the issues found by the auditors.
- Issuance of an interim audit report.
- Double-check all the found issues to make sure they are relevant and the determined threat level is correct.
- Provide the Client with an interim report.
- The Client either fixes the issues or provides comments on the issues found by the auditors. Feedback from the Customer must be received on every issue/bug so that the Contractor can assign them a status (either "fixed" or "acknowledged").
- Upon completion of the bug fixing, the auditors double-check each fix and assign it a specific status, providing a proof link to the fix.
- A re-audited report is issued.
- Verify the fixed code version with all the recommendations and its statuses.
- Provide the Client with a re-audited report.
- The Customer deploys the re-audited source code on the mainnet.
- The Contractor verifies the deployed code with the re-audited version and checks them for compliance.
- If the versions of the code match, the Contractor issues a public audit report.
- Conduct the final check of the code deployed on the mainnet.
- Provide the Customer with a public audit report.
All vulnerabilities discovered during the audit are classified based on their potential severity and have the following classification:
| Severity | Description |
|---|---|
| Critical | Bugs leading to assets theft, fund access locking, or any other loss of funds. |
| High | Bugs that can trigger a contract failure. Further recovery is possible only by manual modification of the contract state or replacement. |
| Medium | Bugs that can break the intended contract logic or expose it to DoS attacks, but do not cause direct loss funds. |
| Low | Bugs that do not have a significant immediate impact and could be easily fixed. |
Based on the feedback received from the Customer regarding the list of findings discovered by the Contractor, they are assigned the following statuses:
| Status | Description |
|---|---|
| Fixed | Recommended fixes have been made to the project code and no longer affect its security. |
| Acknowledged | The Customer is aware of the finding. Recommendations for the finding are planned to be resolved in the future. |
This project implements a Merkle tree-based contract for securely airdropping ETH to eligible recipients. The contract, called MerkleAirdrop, uses a Merkle tree to efficiently verify and distribute airdrop amounts to multiple recipients. It allows the contract owner to set a Merkle root, which represents the list of eligible addresses and their corresponding ETH amounts.
| Title | Description |
|---|---|
| Client | P2P.org |
| Project name | ETH Allocation Share |
| Timeline | 21.10.2024 - 22.10.2024 |
| Number of Auditors | 3 |
| Date | Commit Hash | Note |
|---|---|---|
| 21.10.2024 | dd05a846fc427b92b9fd60c8aeed990b16270286 | Commit for the audit |
| 22.10.2024 | f6bc15e5d658024dd8537ece49655f86c3cb9111 | Commit for the re-audit |
The audit covered the following files:
| File name | Link |
|---|---|
| src/MerkleAirdrop.sol | https://github.com/p2p-org/eth-merkle-drop/blob/dd05a846fc427b92b9fd60c8aeed990b16270286/src/MerkleAirdrop.sol |
| File name | Contract deployed on mainnet | Comment |
|---|---|---|
| MerkleAirdrop.sol | 0xA2431B0f7937830E48E113380BB5ADe7eDD50F6e |
| Severity | # of Findings |
|---|---|
| CRITICAL | 0 |
| HIGH | 0 |
| MEDIUM | 0 |
| LOW | 3 |
During the audit, we thoroughly tested critical attack vectors and verified the following:
-
Potential Reentrancy Attack on the
claimFunction: The contract follows the Checks-Effects-Interactions pattern, effectively preventing reentrancy attacks. In theclaimfunction, the state variableclaimed[msg.sender]is updated before the ETH is transferred to the claimant, ensuring that no reentrancy can occur because the user's claim status is marked before any external interaction. -
Correctness of the Merkle Proof or Leaf Calculation: The contract calculates the Merkle tree leaf correctly using
keccak256(abi.encodePacked(msg.sender, _amount)). This ensures that the leaf corresponds to the recipient and the claimed amount. The Merkle proof verification is implemented properly using OZMerkleProof.verify, preventing manipulation of the proof or any miscalculation of the leaf. -
Front-running User Claims: The contract's design prevents front-running attacks since the Merkle tree leaf is computed using
msg.sender, binding the claim directly to the caller's address. This ensures that no malicious actor can front-run a legitimate claim by submitting a transaction with a higher gas price, as only the intended recipient's address will pass the verification process. -
Appropriate Access Controls for Critical Functions: The
setMerkleRootandrecoverEtherfunctions are secured with theonlyOwnermodifier, ensuring that only the contract owner can update the Merkle root or recover unclaimed Ether. -
Handling of Unclaimed Ether: Any unclaimed Ether in the contract will not be lost because the contract includes a
recoverEther()function. This function allows the owner to withdraw the remaining balance of the contract at any time.
Not found
Not found
Not found
Fixed in https://github.com/p2p-org/eth-merkle-drop/commit/f6bc15e5d658024dd8537ece49655f86c3cb9111
MerkleAirdrop.setMerkleRoot() allows updating the merkleRoot to the same value it already holds, which could make it more difficult to detect potential errors in the root updates.
The issue is classified as Low severity because it does not introduce direct security risks but may impact the protection against owner's errors.
We recommend adding a check to ensure that the new merkleRoot is different from the current value before updating it.
Fixed in https://github.com/p2p-org/eth-merkle-drop/commit/f6bc15e5d658024dd8537ece49655f86c3cb9111
Fixed in https://github.com/p2p-org/eth-merkle-drop/commit/f6bc15e5d658024dd8537ece49655f86c3cb9111
This issue has been identified within the recoverEther function of the MerkleAirdrop contract.
The function does not check whether the _recipient address is a zero address before attempting to transfer the contract's balance. This could result in the loss of funds if a zero address is mistakenly passed as the recipient.
The issue is classified as Low severity because in rare cases it can lead to funds loss.
We recommend adding a check to ensure that _recipient is not a zero address before transferring the balance.
Fixed in https://github.com/p2p-org/eth-merkle-drop/commit/f6bc15e5d658024dd8537ece49655f86c3cb9111
Acknowledged
If a user has already claimed their airdrop before the merkleRoot is updated, and in the new version of the tree the user is entitled to more tokens, they will not be able to claim the added amount under the new root.
The issue is classified as Low severity because it impacts only those users who have claimed before the merkleRoot update, and this scenario is not highly likely to occur frequently.
We recommend storing how many tokens a user has already claimed and allowing an additional claim if the new version of the tree entitles the user to more tokens.
Acknowledged. We don't plan to update the
merkleRootonce the claiming has started. It would make the accounting messy anyway since the new root might imply lower amounts than already claimed. In case of emergency, we plan to userecoverEtherand deploy a new instance of theMerkleAirdropcontract instead.
MixBytes is a team of blockchain developers, auditors and analysts keen on decentralized systems. We build opensource solutions, smart contracts and blockchain protocols, perform security audits, work on benchmarking and software testing solutions, do research and tech consultancy.