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Earn Contracts - Send

Prepared by:

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HALBORN

Last Updated 03/18/2025

Date of Engagement: March 5th, 2025 - March 7th, 2025

Summary

100% of all REPORTED Findings have been addressed

All findings

3

Critical

0

High

0

Medium

0

Low

0

Informational

3

Table of Contents

1. Introduction

Send Earn Protocol engaged Halborn to conduct a security assessment on their smart contracts beginning on March 5th, 2025 and ending on March 7th, 2025. The security assessment was scoped to the smart contracts provided to Halborn. Commit hashes and further details can be found in the Scope section of this report.


The Send Earn Protocol codebase in scope consists of permissionless, non-custodial USDC vaults with built-in referral rewards for community-driven yield generation.

2. Assessment Summary

Halborn was provided 3 days for the engagement and assigned 1 full-time security engineer to review the security of the smart contracts in scope. The engineer is a blockchain and smart contract security expert with advanced penetration testing and smart contract hacking skills, and deep knowledge of multiple blockchain protocols.


The purpose of the assessment is to:

    • Identify potential security issues within the smart contracts.

    • Ensure that smart contract functionality operates as intended.


In summary, Halborn identified some improvements to reduce the likelihood and impact of risks, which were mostly addressed by the Send Earn Protocol team. The main ones are the following:

    • Implement input validation to ensure that the input addresses are not 0.

    • Remove the duplicated code from the contract.


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 this 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 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 led to arithmetic related vulnerabilities.

    • Local testing with custom scripts (Foundry).

    • Fork testing against main networks (Foundry).

    • Static analysis of security for scoped contract, and imported functions (Slither).


4. Static Analysis Report

4.1 Description

Halborn used automated testing techniques to enhance the coverage of certain areas of the smart contracts in scope. Among the tools used was Slither, a Solidity static analysis framework. After Halborn verified the smart contracts in the repository and was able to compile them correctly into their abis and binary format, Slither was run against the contracts. This tool can statically verify mathematical relationships between Solidity variables to detect invalid or inconsistent usage of the contracts' APIs across the entire code-base.


The security team assessed all findings identified by the Slither software, however, findings with related to external dependencies are not included in the below results for the sake of report readability.

4.2 Output

The findings obtained as a result of the Slither scan were reviewed, and many were not included in the report because they were determined as false positives.





5. 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.

5.1 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

5.2 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 (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
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}

5.3 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

6. SCOPE

Files and Repository
(a) Repository: send-earn-contracts
(b) Assessed Commit ID: 6159a69
(c) Items in scope:
  • src/Platform.sol
  • src/SendEarn.sol
  • src/SendEarnAffiliate.sol
↓ Expand ↓
Out-of-Scope: Third party dependencies and economic attacks.
Remediation Commit ID:
Out-of-Scope: New features/implementations after the remediation commit IDs.

7. Assessment Summary & Findings Overview

Critical

0

High

0

Medium

0

Low

0

Informational

3

Security analysisRisk levelRemediation Date
Unrestricted functions allow for token movementsInformationalAcknowledged - 03/11/2025
Missing input validationInformationalSolved - 03/11/2025
Duplicated codeInformationalSolved - 03/11/2025

8. Findings & Tech Details

8.1 Unrestricted functions allow for token movements

//

Informational

Description

The SendEarn contract includes a collect() function with no access restrictions:

function collect(address token) external {
    if (collections == address(0)) revert Errors.ZeroAddress();

    uint256 amount = IERC20(token).balanceOf(address(this));

    IERC20(token).safeTransfer(collections, amount);

    emit Events.Collect(_msgSender(), token, amount);
}

Similarly, the SendEarnAffiliate contract contains an unrestricted pay() function that anyone can call:

function pay(IERC4626 vault) external {
    IERC20 asset = IERC20(vault.asset());
    if (address(asset) != address(payVault.asset())) revert Errors.AssetMismatch();
    // find the amount of tokens to pay
    uint256 amount = vault.balanceOf(address(this));
    if (amount == 0) revert Errors.ZeroAmount();

    // convert to the underlying asset
    uint256 assets = vault.redeem(amount, address(this), address(this));

    // calculate the split
    uint256 split = splitConfig.split();
    uint256 platformSplit = assets.mulDiv(split, Constants.SPLIT_TOTAL);
    uint256 affiliateSplit = assets.mulDiv(Constants.SPLIT_TOTAL - split, Constants.SPLIT_TOTAL);

    // transfer the split to the platform and affiliate
    platformVault.deposit(platformSplit, splitConfig.platform());
    payVault.deposit(affiliateSplit, affiliate);

    emit Events.AffiliatePay(msg.sender, address(vault), address(asset), assets, platformSplit, affiliateSplit);
}

Even though tokens are only sent to a trusted address, the lack of access control means that users can unexpectedly trigger token movements that might disrupt operations or cause accounting issues at inopportune times.

BVSS
Recommendation

If public access is intentional, document this behavior in the protocol's technical documentation and explain the rationale. If not intended, add appropriate access control to both functions.

Remediation Comment

ACKNOWLEDGED: The Send Earn Protocol team made a business decision to acknowledge this finding and not alter the contracts.


References
0xsend/send-earn-contracts/src/SendEarn.sol#L118-L126
0xsend/send-earn-contracts/src/SendEarnAffiliate.sol#L48-L68

8.2 Missing input validation

//

Informational

Description

Some functions throughout the contracts in scope lack input validation. Instances of this issue include:

- SendEarn.setFeeRecipient()

- SendEarn.setCollections()


BVSS
Recommendation

Implement input validation to ensure that the input addresses are not 0.

Remediation Comment

SOLVED: The Send Earn Protocol team solved this finding in commit 646d000 by following the mentioned recommendation.

Remediation Hash
https://github.com/0xsend/send-earn-contracts/commit/646d0006ca43fe14afa8270cc3a20267bf5782ec
References
0xsend/send-earn-contracts/src/SendEarn.sol#L102-L113

8.3 Duplicated code

//

Informational

Description

In the Platform contract, there's a redundant event emission in the platform management functions. When setPlatform() is called, it internally calls _setPlatform() which emits the Events.SetPlatform(newPlatform) event. However, after this call, setPlatform() also emits the exact same event with the same parameter:

function setPlatform(address newPlatform) external onlyPlatform {
  if (newPlatform == platform()) revert Errors.AlreadySet();
  _setPlatform(newPlatform);
  emit Events.SetPlatform(newPlatform); // Duplicate emission
}

function _setPlatform(address newPlatform) internal {
  if (newPlatform == platform()) revert Errors.AlreadySet();
  if (newPlatform == address(0)) revert Errors.ZeroAddress();
  _platform = newPlatform;
  emit Events.SetPlatform(newPlatform); // Already emitted here
}

Additionally, there's a duplicated error check (if (newPlatform == platform()) revert Errors.AlreadySet();) that appears in both functions.

BVSS
Recommendation

Remove the duplicated code from the contract.

Remediation Comment

SOLVED: The Send Earn Protocol team solved this finding in commit c575d46 by following the mentioned recommendation.

Remediation Hash
https://github.com/0xsend/send-earn-contracts/commit/c575d4680866c227044de83aa18007df1f24a894
References
0xsend/send-earn-contracts/src/Platform.sol#L50-L54
0xsend/send-earn-contracts/src/Platform.sol#L97-L104

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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