Soroban zkCrossDex - ZKCross

Prepared by:

HALBORN

Last Updated 09/15/2025

Date of Engagement: August 18th, 2025 - August 22nd, 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 methodology
4. Risk methodology
5. Scope
6. Assessment summary & findings overview
7. Findings & Tech Details

7.1 Protocol revenue permanently lost when revenue address not set
7.2 User funds stuck without recourse when cross-chain transfer fails
7.3 Contract cannot be halted during security incidents
7.4 Disabled lock feature when fee set to zero
7.5 Usdc minimum protection ineffective on stellar network
7.6 Missing revenue tracking
7.7 Revenue address cannot be changed if compromised
7.8 Lock-hash lifecycle mis-management allows either replay attacks or rent dos
7.9 External token calls and reentrancy surfaces in lock and release
7.10 Indexer confusion from redundant token parameters
7.11 Event monitoring blind spots from inconsistent naming
7.12 Unnecessary computation overhead in validation path
7.13 Performance overhead from unnecessary memory cloning

1. Introduction

The security assessment was commissioned by ZKCross, a cross-chain interoperability protocol focused on DeFi infrastructure, to assess the security and robustness of the Rust-based Stellar LockAndRelease smart contract. The assessment was performed by Halborn’s experienced security team, focusing on the code released at commit faa29f7. The review covered all functionality in contracts/lock_release/src/lib.rs between August 25th, 2025, and August 27th, 2025. The primary objective of this engagement’s core purpose was to identify vulnerabilities, ensure protocol reliability and strengthen overall security.

2. Assessment Summary

The team at Halborn assigned a full-time security engineer to verify the security of the smart contracts. The security engineer is a blockchain and smart-contract security expert 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 contract

In summary, Halborn identified some improvements to reduce the likelihood and impact of risks, which were addressed and properly solved by the ZKCross team. The main findings were the following:

Reject lock() calls if RevenueSet has not yet been established, or allow the owner to sweep residual fees once a revenue address has been configured.
Introduce a pending state with expiry for each lock; admins must release it before expiry, or users can refund.
Add a global paused flag, controlled by the owner/admin, to restrict lock/release actions.
Enforce percentage in the range 1..=2000, or handle 0 as a special case by skipping min_amount and safely setting fee = 0.

3. Test Approach and Methodology

The assessment combined structured manual code review, requirements verification, and automated testing. Key steps included:

Review of functional and threat modeling documentation (data flows, STRIDE methodology)
Manual source review for logic errors, state machine soundness, replay/reentrancy surfaces, and access control correctness
Execution of the project’s public unit and on-chain test suite to validate specification adherence and stress system invariants

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: SorobanContract_Stellar_zkCrossDex

(b) Assessed Commit ID: faa29f7

contracts/lock_release/src/lib.rs

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

High

Medium

Low

Informational

Security analysis	Risk level	Remediation Date
Protocol Revenue Permanently Lost When Revenue Address Not Set	Low	Solved - 09/08/2025
User Funds Stuck Without Recourse When Cross-Chain Transfer Fails	Low	Solved - 09/15/2025
Contract Cannot Be Halted During Security Incidents	Low	Solved - 09/08/2025
Disabled Lock Feature When Fee Set to Zero	Low	Solved - 09/08/2025
USDC Minimum Protection Ineffective on Stellar Network	Low	Solved - 09/08/2025
Missing Revenue Tracking	Low	Solved - 09/08/2025
Revenue Address Cannot Be Changed If Compromised	Informational	Solved - 09/08/2025
Lock-hash lifecycle mis-management allows either replay attacks or rent DoS	Informational	Solved - 09/08/2025
External token calls and reentrancy surfaces in lock and release	Informational	Solved - 09/08/2025
Indexer Confusion from Redundant Token Parameters	Informational	Solved - 09/08/2025
Event Monitoring Blind Spots from Inconsistent Naming	Informational	Solved - 09/08/2025
Unnecessary Computation Overhead in Validation Path	Informational	Solved - 09/08/2025
Performance Overhead from Unnecessary Memory Cloning	Informational	Solved - 09/08/2025

https://github.com/Dev-zkCross/SorobanContract_Stellar_zkCrossDex/commit/8c6a4ef4ec73e06c254789776794fd7985091d73

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 methodology
4. Risk methodology
5. Scope
6. Assessment summary & findings overview
7. Findings & Tech Details

7.1 Protocol revenue permanently lost when revenue address not set
7.2 User funds stuck without recourse when cross-chain transfer fails
7.3 Contract cannot be halted during security incidents
7.4 Disabled lock feature when fee set to zero
7.5 Usdc minimum protection ineffective on stellar network
7.6 Missing revenue tracking
7.7 Revenue address cannot be changed if compromised
7.8 Lock-hash lifecycle mis-management allows either replay attacks or rent dos
7.9 External token calls and reentrancy surfaces in lock and release
7.10 Indexer confusion from redundant token parameters
7.11 Event monitoring blind spots from inconsistent naming
7.12 Unnecessary computation overhead in validation path
7.13 Performance overhead from unnecessary memory cloning

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