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Transfer and Earn - Moonwell

Prepared by:

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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

Every vulnerability and issue observed by Halborn is ranked based on two sets of Metrics and a Severity Coefficient. This system is inspired by the industry standard Common Vulnerability Scoring System.
The two Metric sets are: Exploitability and Impact. Exploitability captures the ease and technical means by which vulnerabilities can be exploited and Impact describes the consequences of a successful exploit.
The Severity Coefficients is designed to further refine the accuracy of the ranking with two factors: Reversibility and Scope. These capture the impact of the vulnerability on the environment as well as the number of users and smart contracts affected.
The final score is a value between 0-10 rounded up to 1 decimal place and 10 corresponding to the highest security risk. This provides an objective and accurate rating of the severity of security vulnerabilities in smart contracts.
The system is designed to assist in identifying and prioritizing vulnerabilities based on their level of risk to address the most critical issues in a timely manner.

4.1 EXPLOITABILITY

Attack Origin (AO):
Captures whether the attack requires compromising a specific account.
Attack Cost (AC):
Captures the cost of exploiting the vulnerability incurred by the attacker relative to sending a single transaction on the relevant blockchain. Includes but is not limited to financial and computational cost.
Attack Complexity (AX):
Describes the conditions beyond the attacker’s control that must exist in order to exploit the vulnerability. Includes but is not limited to macro situation, available third-party liquidity and regulatory challenges.
Metrics:
EXPLOITABILITY METRIC (mem_e)METRIC VALUENUMERICAL 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
Exploitability EE is calculated using the following formula:

E=∏meE = \prod m_e

4.2 IMPACT

Confidentiality (C):
Measures the impact to the confidentiality of the information resources managed by the contract due to a successfully exploited vulnerability. Confidentiality refers to limiting access to authorized users only.
Integrity (I):
Measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of data stored and/or processed on-chain. Integrity impact directly affecting Deposit or Yield records is excluded.
Availability (A):
Measures the impact to the availability of the impacted component resulting from a successfully exploited vulnerability. This metric refers to smart contract features and functionality, not state. Availability impact directly affecting Deposit or Yield is excluded.
Deposit (D):
Measures the impact to the deposits made to the contract by either users or owners.
Yield (Y):
Measures the impact to the yield generated by the contract for either users or owners.
Metrics:
IMPACT METRIC (mIm_I)METRIC VALUENUMERICAL VALUE
Confidentiality (C)None (C:N)
Low (C:L)
Medium (C:M)
High (C:H)
Critical (C: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
Impact II is calculated using the following formula:

I=max(mI)+∑mI−max(mI)4I = max(m_I) + \frac{\sum{m_I} - max(m_I)}{4}

4.3 SEVERITY COEFFICIENT

Reversibility (R):
Describes the share of the exploited vulnerability effects that can be reversed. For upgradeable contracts, assume the contract private key is available.
Scope (S):
Captures whether a vulnerability in one vulnerable contract impacts resources in other contracts.
Metrics:
SEVERITY COEFFICIENT (CC)COEFFICIENT VALUENUMERICAL VALUE
Reversibility (rr)None (R:N)
Partial (R:P)
Full (R:F)		1
0.5
0.25
Scope (ss)Changed (S:C)
Unchanged (S:U)		1.25
1
Severity Coefficient CC is obtained by the following product:

C=rsC = rs

The Vulnerability Severity Score SS is obtained by:

S=min(10,EIC∗10)S = min(10, EIC * 10)

The score is rounded up to 1 decimal places.
SeverityScore Value Range
Critical9 - 10
High7 - 8.9
Medium4.5 - 6.9
Low2 - 4.4
Informational0 - 1.9

5. SCOPE

REPOSITORY
(a) Repository: mamo-contracts
(b) Assessed Commit ID: 86bd51e
(c) Items in scope:
  • src/TransferAndEarn.sol
Out-of-Scope: Third party dependencies and economic attacks.
Remediation Commit ID:
Out-of-Scope: New features/implementations after the remediation commit IDs.

6. Assessment Summary & Findings Overview

Critical

0

High

0

Medium

0

Low

1

Informational

3

Security analysisRisk levelRemediation Date
Missing zero-address validation for feeCollectorLowSolved - 08/22/2025
Use of Ownable library with single-step ownership transferInformationalAcknowledged - 08/22/2025
Use of custom errors instead of revert stringsInformationalAcknowledged - 08/22/2025
Owner can renounce ownershipInformationalAcknowledged - 08/22/2025

7. Findings & Tech Details

7.1 Missing zero-address validation for feeCollector

//

Low

Description
BVSS
Recommendation
Remediation Comment
Remediation Hash
https://github.com/moonwell-fi/mamo-contracts/pull/42/commits/5c55e5d1462d12ccba675b9c1f5b2c95672c673d

7.2 Use of Ownable library with single-step ownership transfer

//

Informational

Description
BVSS
Recommendation
Remediation Comment

7.3 Use of custom errors instead of revert strings

//

Informational

Description
BVSS
Recommendation
Remediation Comment

7.4 Owner can renounce ownership

//

Informational

Description
BVSS
Recommendation
Remediation Comment

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.

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