Prepared by:
HALBORN
Last Updated 08/27/2025
Date of Engagement: August 18th, 2025 - August 20th, 2025
Summary
100% of all REPORTED Findings have been addressed
All findings
4
Critical
0
High
0
Medium
0
Low
1
Informational
3
Table of Contents
1. Introduction
Moonwell engaged Halborn to conduct a security assessment on their smart contracts beginning on August 18th, 2025 and ending on August 19th, 2025. The security assessment was scoped to the smart contracts provided to the Halborn team. Commit hashes and further details can be found in the Scope section of this report.
2. Assessment summary
The team at Halborn assigned one full-time security engineer to assess the security of the smart contracts. The security engineers are blockchain and smart-contract security experts with advanced penetration testing, smart-contract hacking, and deep knowledge of multiple blockchain protocols.
The purpose of this assessment is to:
Ensure that smart contract functions operate as intended.
Identify potential security issues with the smart contracts.
In summary, Halborn identified some improvements to reduce the likelihood and impact of risks, which were partially addressed by the Moonwell team. The main ones were the following:
Implement a two-step process where the owner nominates an account and the nominated account needs to call an acceptOwnership function for the transfer of the ownership to fully succeed.Replace all revert strings with custom errors.Add a zero-address check in the constructor, consistent with the setFeeCollector function.Consider disallowing the owner address to be set to address(0).
3. Test approach and methodology
Halborn performed a combination of manual review of the code and automated security testing to balance efficiency, timeliness, practicality, and accuracy in regard to the scope of the smart contract assessment. While manual testing is recommended to uncover flaws in logic, process, and implementation; automated testing techniques help enhance coverage of smart contracts and can quickly identify items that do not follow security best practices. The following phases and associated tools were used throughout the term of the assessment:
Research into the architecture, purpose, and use of the platform.
Smart contract manual code review and walkthrough to identify any logic issue.
Thorough assessment of safety and usage of critical Solidity variables and functions in scope that could lead to arithmetic related vulnerabilities.
Manual testing by custom scripts.
Graphing out functionality and contract logic/connectivity/functions (
solgraph).Static Analysis of security for scoped contract, and imported functions. (
Slither).Local or public testnet deployment (
Foundry,Remix IDE).
4. RISK METHODOLOGY
4.1 EXPLOITABILITY
Attack Origin (AO):
Attack Cost (AC):
Attack Complexity (AX):
Metrics:
| EXPLOITABILITY METRIC () | METRIC VALUE | NUMERICAL VALUE |
|---|---|---|
| Attack Origin (AO) | Arbitrary (AO:A) Specific (AO:S) | 1 0.2 |
| Attack Cost (AC) | Low (AC:L) Medium (AC:M) High (AC:H) | 1 0.67 0.33 |
| Attack Complexity (AX) | Low (AX:L) Medium (AX:M) High (AX:H) | 1 0.67 0.33 |
4.2 IMPACT
Confidentiality (C):
Integrity (I):
Availability (A):
Deposit (D):
Yield (Y):
Metrics:
| IMPACT METRIC () | METRIC VALUE | NUMERICAL VALUE |
|---|---|---|
| Confidentiality (C) | None (I:N) Low (I:L) Medium (I:M) High (I:H) Critical (I:C) | 0 0.25 0.5 0.75 1 |
| Integrity (I) | None (I:N) Low (I:L) Medium (I:M) High (I:H) Critical (I:C) | 0 0.25 0.5 0.75 1 |
| Availability (A) | None (A:N) Low (A:L) Medium (A:M) High (A:H) Critical (A:C) | 0 0.25 0.5 0.75 1 |
| Deposit (D) | None (D:N) Low (D:L) Medium (D:M) High (D:H) Critical (D:C) | 0 0.25 0.5 0.75 1 |
| Yield (Y) | None (Y:N) Low (Y:L) Medium (Y:M) High (Y:H) Critical (Y:C) | 0 0.25 0.5 0.75 1 |
4.3 SEVERITY COEFFICIENT
Reversibility (R):
Scope (S):
Metrics:
| SEVERITY COEFFICIENT () | COEFFICIENT VALUE | NUMERICAL VALUE |
|---|---|---|
| Reversibility () | None (R:N) Partial (R:P) Full (R:F) | 1 0.5 0.25 |
| Scope () | Changed (S:C) Unchanged (S:U) | 1.25 1 |
| Severity | Score Value Range |
|---|---|
| Critical | 9 - 10 |
| High | 7 - 8.9 |
| Medium | 4.5 - 6.9 |
| Low | 2 - 4.4 |
| Informational | 0 - 1.9 |
5. SCOPE
- src/TransferAndEarn.sol
6. Assessment Summary & Findings Overview
Critical
0
High
0
Medium
0
Low
1
Informational
3
| Security analysis | Risk level | Remediation Date |
|---|---|---|
| Missing zero-address validation for feeCollector | Low | Solved - 08/22/2025 |
| Use of Ownable library with single-step ownership transfer | Informational | Acknowledged - 08/22/2025 |
| Use of custom errors instead of revert strings | Informational | Acknowledged - 08/22/2025 |
| Owner can renounce ownership | Informational | Acknowledged - 08/22/2025 |
7. Findings & Tech Details
7.1 Missing zero-address validation for feeCollector
//
Description
In the constructor, feeCollector is set without checking for address(0).
constructor(address _feeCollector, address _owner) Ownable(_owner) {
feeCollector = _feeCollector;
}If the contract is deployed with a zero address, subsequent calls to earn will attempt to safeTransfer ERC20 tokens to address(0).
BVSS
Recommendation
It is recommended to add a zero-address check in the constructor, consistent with the setFeeCollector function.
Remediation Comment
SOLVED : The Moonwell team solved the issue. Validation was implemented.
Remediation Hash
7.2 Use of Ownable library with single-step ownership transfer
//
Description
The ownership of the contract can be lost as the TransferAndEarn inherited from the Ownable contract and their ownership can be transferred in a single-step process. The address the ownership is changed to should be verified to be active or willing to act as the owner.
BVSS
Recommendation
It is recommended to implement a two-step process where the owner nominates an account and the nominated account needs to call an acceptOwnership function for the transfer of the ownership to fully succeed. This ensures the nominated EOA account is a valid and active account. This can be achieved by using OpenZeppelin’s Ownable2Step contract instead of the Ownable.
Remediation Comment
ACKNOWLEDGED : The Moonwell team acknowledged the issue.
7.3 Use of custom errors instead of revert strings
//
Description
Throughout the entire codebases, require statements are used. In Solidity development, replacing hard-coded revert message strings with the Error() syntax is an optimization strategy that can significantly reduce gas costs. Hardcoded strings, stored on the blockchain, increase the size and cost of deploying and executing contracts. The Error() syntax allows for the definition of reusable, parameterized custom errors, leading to a more efficient use of storage and reduced gas consumption.
This approach not only optimizes gas usage during deployment and interaction with the contract but also enhances code maintainability and readability by providing clearer, context-specific error information.
BVSS
Recommendation
It is recommended to replace all revert strings with custom errors. Since the protocol uses Solidity 0.8.28, custom errors can also be embedded directly within require statements, enabling gas-efficient error handling without requiring explicit revert calls.
Remediation Comment
ACKNOWLEDGED : The Moonwell team acknowledged the issue.
7.4 Owner can renounce ownership
//
Description
The TransferAndEarn contract indirectly inherits from Ownable. In this contract contract, the renounceOwnership function is used to renounce the owner permission.
function renounceOwnership() public virtual onlyOwner {
_transferOwnership(address(0));
}Renouncing ownership before transferring would result in the contract having no owner, eliminating the ability to call privileged functions.
BVSS
Recommendation
Consider disallowing the owner address to be set to address(0).
Remediation Comment
ACKNOWLEDGED : The Moonwell team acknowledged the issue.
Halborn strongly recommends conducting a follow-up assessment of the project either within six months or immediately following any material changes to the codebase, whichever comes first. This approach is crucial for maintaining the project’s integrity and addressing potential vulnerabilities introduced by code modifications.
Table of Contents
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