ATokenOTC - Colend

Prepared by:

HALBORN

Last Updated 12/12/2025

Date of Engagement: December 4th, 2025 - December 4th, 2025

Summary

100% of all REPORTED Findings have been addressed

All findings

Critical

High

Medium

Low

Informational

1. Introduction
2. Assessment summary
3. Test approach and methodolody
4. Risk methodology
5. Scope
6. Assessment summary & findings overview
7. Findings & Tech Details

7.1 Unused variables and interface
7.2 Setmaxoffersperwallet allows setting new limit equal to existing limit
7.3 Ownership transfer uses single-step pattern
7.4 Outdated solidity pragma version

1. INTRODUCTION

Colend engaged Halborn to perform a security assessment of their smart contracts starting and ending on December 4th, 2025. The assessment scope was limited to the smart contracts provided to Halborn. Commit hashes and additional details are available in the Scope section of this report.

The ATokenOTC codebase in scope consists of a non-custodial OTC trading smart contract designed to create, manage, and fill offers involving Receipt Tokens and their underlying ERC-20 assets. The system implements offer lifecycle functionality with configurable per-wallet limits, an optional allowlist for supported aTokens, and pausing controls via an Ownable admin.

2. ASSESSMENT SUMMARY

Halborn was allocated 1 day for this engagement and assigned 1 full-time security engineers to conduct a comprehensive review of the smart contracts within scope. The engineers are experts in blockchain and smart contract security, with advanced skills in penetration testing and smart contract exploitation, as well as extensive knowledge of multiple blockchain protocols.

The objectives of this assessment are to:

Identify potential security vulnerabilities within the smart contracts.
Verify that the smart contract functionality operates as intended.

In summary, Halborn identified several areas for improvement to reduce the likelihood and impact of security risks, which were mostly addressed by the Colend team.The main recommendations were:

If not intended, remove POOL_ADDRESS and IPool.
Implement a two-step ownership transfer process.
Upgrade to the latest stable version.
Add a check to ensure newLimit differs from the current limit before allowing the update.

3. TEST APPROACH AND METHODOLODY

Halborn conducted a combination of manual code review and automated security testing to balance efficiency, timeliness, practicality, and accuracy within the scope of this assessment. While manual testing is crucial for identifying flaws in logic, processes, and implementation, automated testing enhances coverage of smart contracts and quickly detects deviations from established security best practices.

The following phases and associated tools were employed throughout the term of the assessment:

Research into the platform's architecture, purpose and use.
Manual code review and walkthrough of smart contracts to identify any logical issues.
Comprehensive assessment of the safety and usage of critical Solidity variables and functions within scope that could lead to arithmetic-related vulnerabilities.
Local testing using custom scripts (Foundry).
Fork testing against main networks (Foundry).
Static security analysis of scoped contracts, and imported functions (Slither).

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 ( $m_e$ )	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

Exploitability

E

is calculated using the following formula:

$E = \prod m_e$

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 ( $m_I$ )	METRIC VALUE	NUMERICAL 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

I

is calculated using the following formula:

$I = max(m_I) + \frac{\sum{m_I} - max(m_I)}{4}$

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 ( $C$ )	COEFFICIENT VALUE	NUMERICAL VALUE
Reversibility ( $r$ )	None (R:N) Partial (R:P) Full (R:F)	1 0.5 0.25
Scope ( $s$ )	Changed (S:C) Unchanged (S:U)	1.25 1

Severity Coefficient

C

is obtained by the following product:

$C = rs$

The Vulnerability Severity Score

S

is obtained by:

$S = min(10, EIC * 10)$

The score is rounded up to 1 decimal places.

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

REPOSITORY

(a) Repository: otc-market-project

(b) Assessed Commit ID: bfe4b65

contracts/src/ATokenOTC.sol

Out-of-Scope: External dependencies and economic attacks.

Remediation Commit ID:

Out-of-Scope: New features/implementations after the remediation commit IDs.

6. Assessment Summary & Findings Overview

Critical

High

Medium

Low

Informational

Security analysis	Risk level	Remediation Date
Unused Variables and Interface	Informational	Solved - 12/04/2025
setMaxOffersPerWallet Allows Setting New Limit Equal to Existing Limit	Informational	Solved - 12/04/2025
Ownership Transfer Uses Single-Step Pattern	Informational	Acknowledged - 12/05/2025
Outdated Solidity Pragma Version	Informational	Solved - 12/04/2025

7. Findings & Tech Details

7.1 Unused Variables and Interface

Informational

Description

BVSS

AO:A/AC:L/AX:M/R:N/S:U/C:N/A:N/I:L/D:N/Y:N (1.7)

Recommendation

Remediation Comment

Remediation Hash

https://github.com/tobyColend/otc-market-project/commit/139e12d4b869f57ebc837413ee4049eb8a69e6b2

7.2 setMaxOffersPerWallet Allows Setting New Limit Equal to Existing Limit

Informational

Description

BVSS

AO:A/AC:L/AX:M/R:N/S:U/C:N/A:N/I:L/D:N/Y:N (1.7)

Recommendation

Remediation Comment

Remediation Hash

https://github.com/tobyColend/otc-market-project/commit/08494fb38ff5413de7f782fa74c55d2819baeecc

7.3 Ownership Transfer Uses Single-Step Pattern

Informational

Description

BVSS

AO:A/AC:L/AX:M/R:N/S:U/C:N/A:N/I:L/D:N/Y:N (1.7)

Recommendation

Remediation Comment

7.4 Outdated Solidity Pragma Version

Informational

Description

BVSS

AO:A/AC:L/AX:M/R:N/S:U/C:N/A:N/I:L/D:N/Y:N (1.7)

Recommendation

Remediation Comment

Remediation Hash

https://github.com/tobyColend/otc-market-project/commit/d01f6b8da8df8b40ddb3f5b8e3cb5669cb394887

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.

1. Introduction
2. Assessment summary
3. Test approach and methodolody
4. Risk methodology
5. Scope
6. Assessment summary & findings overview
7. Findings & Tech Details

ATokenOTC

Colend

Table of Contents

1. INTRODUCTION

2. ASSESSMENT SUMMARY

3. TEST APPROACH AND METHODOLODY

4. RISK METHODOLOGY

4.1 EXPLOITABILITY

Attack Origin (AO):

Attack Cost (AC):

Attack Complexity (AX):

Metrics:

4.2 IMPACT

Confidentiality (C):

Integrity (I):

Availability (A):

Deposit (D):

Yield (Y):

Metrics:

4.3 SEVERITY COEFFICIENT

Reversibility (R):

Scope (S):

Metrics:

5. SCOPE

6. Assessment Summary & Findings Overview

7. Findings & Tech Details

7.1 Unused Variables and Interface

Description

BVSS

Recommendation

Remediation Comment

Remediation Hash

7.2 setMaxOffersPerWallet Allows Setting New Limit Equal to Existing Limit

Description

BVSS

Recommendation

Remediation Comment

Remediation Hash

7.3 Ownership Transfer Uses Single-Step Pattern

Description

BVSS

Recommendation

Remediation Comment

7.4 Outdated Solidity Pragma Version

Description

BVSS

Recommendation

Remediation Comment

Remediation Hash

Table of Contents