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Smart Contract Audit

Xend and Wicrypt
December 6, 2023

Table of contents

Summary
Scope of Work
Workflow of the auditing process
Structure and organization of the findings
Manual Report
Test Results

Summary

Vidma team has conducted a smart contract audit for the given codebase.

The contracts are in good condition. Based on the fixes provided by the Ammbr team and on the quality and security of the codebase provided, Vidma team can give a score of 95 to the audited smart contracts.

During the auditing process, the Vidma team has found a couple of informational issues, 7 issues with a low level of severity, 1 issue with a medium level of severity, and 3 issues with a critical level of severity.

Severity of the issue
Total found
Resolved
Unresolved
Critical
3 issues
3 issues
0 issues
High
3 issues
3 issues
0 issues
Medium
3 issues
3 issues
0 issues
Low
3 issues
3 issues
0 issues
Informational
3 issues
3 issues
0 issues
Low
3 issues
3 issues
0 issues

The contracts are in good condition. Based on the fixes provided by the Ammbr team and on the quality and security of the codebase provided, Vidma team can give a score of 95 to the audited smart contracts.

Based on the given findings, risk level, performance, and code style, Vidma team can grant the following overall score:

Please mind that this audit does not certify the definite reliability and security level of the contract. This document describes all vulnerabilities, typos, performance issues, and security issues found by Vidma auditing team. If the code is under development, we recommend run one more audit once the code is finalized.

Summary

Vidma is pleased to present this audit report outlining our assessment of code, smart contracts, and other important audit insights and suggestions for management, developers, and users.The audit scope included BridgeAssist contract. The contract appears to facilitate the transfer of tokens between different blockchain networks, assisted by a relayer. It supports separate fees for sending and fulfilling transactions, works with multiple chains (including non-EVM blockchains), and has configurable limits and exchange rates for cross-chain transactions. Users need to submit a send transaction with the underlying token and chain. The blockchain will search the submitted transactions and sign and fulfill them on the destination chain.During the audit process, the Vidma team found one medium issue which later was considered as invalid due to validation on backend side. A detailed summary and the current state are displayed in the table below.

Severity of the issue Issue severity
Critical
High
Medium
Low
Informational
Total
Severity of the issue Issue severity Total found Resolved Invalid Unresolved
Critical 0 issues 0 issues 0 issues 0 issues
High 0 issues 0 issues 0 issues 0 issues
Medium 0 issues 0 issues 1 issues 0 issues
Low 0 issues 0 issue 0 issue 0 issues
Informational 0 issues 0 issues 0 issues 0 issues
Total 0 issues 0 issues 1 issue 0 issues

After evaluating the findings in this report and the final state after fixes, the Vidma auditors can state that the contracts are fully operational and secure. Under the given circumstances, we set the following risk level:

High Confidence

To set the codebase quality mark, our auditors are evaluating the initial commit given for the scope of the audit and the last commit with the fixes. This approach helps us adequately and sequentially evaluate the quality of the code. Code style, optimization of the contracts, the number of issues, and risk level of the issues are all taken into consideration. The Vidma team has developed a transparent evaluation codebase quality system presented below.

Severity of the issue
Issue severity
Total found
Resolved
Critical
1
10
High
0.8
7
Medium
0.5
5
Low
0.2
0.5
Informational
0
0.1
Please note that the points are deducted out of 100 for each and every issue on the list of findings (according to the current status of the issue). Issues marked as “not valid” are not subject to point deduction.
Codebase quality:
100

Evaluating the initial commit and the last commit with the fixes, Vidma audit team set the following codebase quality mark.

Score
Based on the overall result of the audit and the state of the final reviewed commit, the Vidma audit team grants the following score:

100

In addition to manual check and static analysis, the auditing team has conducted a number of integrated autotests to ensure the given codebase has an adequate performance and security level. The test results and coverage can be found in the accompanying section of this audit report.

Please be aware that this audit does not certify the definitive reliability and security level of the contract. This document describes all vulnerabilities, typos, performance issues, and security issues found by the Vidma audit team.
If the code is still under development, we highly recommend running one more audit once the code is finalized.

Scope of work

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Within the scope of this audit, two independent auditors thoroughly investigated the given codebase and analyzed the overall security and performance of the smart contract.

The audit was conducted from Nov 27, 2023 to Dec 1, 2023. The outcome is disclosed in this document.

The scope of work for the given audit consists of the following contract:

The source code was taken from the following source:

https://github.com/gotbitlabs/wnt-bridge/blob/main/contracts/contracts/BridgeAssist.sol

Initial commit submitted for the audit:

5d1b4efe7bf3e5b2cac1b952944d37db00c30a55

Last commit reviewed by the auditing team:

5d1b4efe7bf3e5b2cac1b952944d37db00c30a55

As a reference to the contracts logic, business concept, and the expected behavior of the codebase, the Xend and Wicrypt team has provided the following documentation:

https://github.com/gotbitlabs/wnt-bridge/tree/main/contracts

The technical documentation is on the readme.

Workflow of the auditing process

Vidma audit team uses the most sophisticated and contemporary methods and well-developed techniques to ensure contracts are free of vulnerabilities and security risks. The overall workflow consists of the following phases:

Phase 1: The research phase

Research

After the Audit kick-off, our security team conducts research on the contract’s logic and expected behavior of the audited contract.

Documentation reading

Vidma auditors do a deep dive into your tech documentation with the aim of discovering all the behavior patterns of your codebase and analyzing the potential audit and testing scenarios.

The outcome

At this point, the Vidma auditors are ready to kick off the process. We set the auditing strategies and methods and are prepared to conduct the first audit part.

Phase 2: Manual part of the audit

Manual check

During the manual phase of the audit, the Vidma team manually looks through the code in order to find any security issues, typos, or discrepancies with the logic of the contract. The initial commit as stated in the agreement is taken into consideration.

Static analysis check

Static analysis tools are used to find any other vulnerabilities in smart contracts that were missed after a manual check.

The outcome

An interim report with the list of issues.

Phase 3: Testing part of the audit

Integration tests

Within the testing part, Vidma auditors run integration tests using the Truffle or Hardhat testing framework. The test coverage and the test results are inserted in the accompanying section of this audit report.

The outcome

Second interim report with the list of new issues found during the testing part of the audit process.

Structure and organization of the findings

For simplicity in reviewing the findings in this report, Vidma auditors classify  the findings in accordance with the severity level of the issues. (from most critical to least critical).

All issues are marked as “Resolved” or “Unresolved”, depending on if they have been fixed by project team or not. The issues with “Not Relevant” status are left on the list of findings but are not eligible for the score points deduction.

The latest commit with the fixes reviewed by the auditors is indicated in the “Scope of Work” section of the report.

The Vidma team always provides a detailed description of the issues and recommendations on how to fix them.

Classification of found issues is graded according to 6 levels of severity described below:

Critical
The issue affects the contract in such a way that funds may be lost or allocated incorrectly, or the issue could result in a significant loss.
Example: Underflow/overflow, precisions, locked funds.
High
The issue significantly affects the ability of the contract to compile or operate. These are potential security or operational issues.
Example: Compilation errors, pausing/unpausing of some functionality, a random value, recursion, the logic that can use all gas from block (too many iterations in the loop), no limitations for locking period, cooldown, arithmetic errors which can cause underflow, etc.
Medium
The issue slightly impacts the contract’s ability to operate by slightly hindering its intended behavior.
Example: Absence of emergency withdrawal of funds, using assert for parameter sanitization.
Low
The issue doesn’t contain operational or security risks, but are more related to optimization of the codebase.
Example: Unused variables, inappropriate function visibility (public instead of external), useless importing of SCs, misuse or disuse of constant and immutable, absent indexing of parameters in events, absent events to track important state changes, absence of getters for important variables, usage of string as a key instead of a hash, etc.
Informational
Are classified as every point that increases onboarding time and code reading, as well as the issues which have no impact on the contract’s ability to operate.
Example: Code style, NatSpec, typos, license, refactoring, naming convention (or unclear naming), layout order, functions order, lack of any type of documentation.

Manual Report

Unsecuring ether transfer

Medium |  Invalid

There is no check in the fulfill() function if the passed FulfillTx is matched with a transaction passed in the send(). So in the FulfillTx struct can be passed arbitrary addresses for fromuser and touser even if there is no available transaction for the passed addresses.

For example: user1 call send with toUser address as user2 address. Then it is possible to submit fulfill() with the fromUser param as user3 and toUser as user3.

Recommendation:

Consider checking the fulfill tx data is matched with the send tx data.

Test Results

To verify the security of the contract and the performance, a number of integration

tests were carried out using the Truffle testing framework.

In this section, we provide both tests written by Xend, Wicrypt and tests written by Vidma auditors.

Vidma Coverage – 100%

Industry Standard – 95%

It is important to note that Vidma auditors do not modify, edit or add tests to the existing tests provided in the Xend and Wicrypt repository. We write totally separate tests with code coverage of a minimum of 95% to meet industry standards.

Tests written by Xend and Wicrypt

Test Coverage

File
BridgeAssist
All Files
File % Stmts % Branch % Funcs % Lines
BridgeAssist 100.00 100.00 100.00 100.00
All Files 100.00 100.00 100.00 100.00

Test Results

Contract: BridgeAssist

  • constructor requires(87ms)
  • should send tokens(141ms)
  • should fulfill tokens from bridge preventing double-spend(82ms)
  • multiple users test(84ms)
  • should take proper fee on fulfill and prevent double-spend(58ms)
  • should not send with bad token(56ms)
  • should not send over the limit(66ms)
  • should withdraw, pause, set chains, set parameters and prevent using incorrect values(253ms)
8 passing(2s)

Tests written by Vidma auditors

Test Coverage

File
BridgeAssist
All Files
File % Stmts % Branch % Funcs % Lines
BridgeAssist 100.00 100.00 100.00 100.00
All Files 100.00 100.00 100.00 100.00

Test Results

Contract: BridgeAssist

  • initialize
  • Should send tokens
  • Should fulfill a transaction
  • Should set relayers
  • Should add chains
  • Should remove chains
  • Should set fees
  • Should set fee wallet
  • Should set limit per send
  • Should withdraw tokens
  • Should pause the contract
  • Should unpause the contract
  • getters
    • Should return user transactions slice
    • Should return user transactions
    • Should return user transactions amount
    • Should return supported chain list
    • Should return relayers length
    • Should return list of relayers
    • Should check if chain is supported
    • Should return current chain name
20 passing(5s)

We are delighted to have a chance to work with the Xend and Wicrypt team and contribute to your company's success by reviewing and certifying the security of your smart contracts.

The statements made in this document should be interpreted neither as investment or legal advice, nor should its authors be held accountable for decisions made based on this document.

Vidma is a security audit company helping crypto companies ensure their code and products operate safely and as intended, enabling founders to sleep soundly at night. We specialize in auditing DeFi protocols, layer one protocols, and marketplace solutions. Our team consists of experienced and internationally trained specialists. Our company is based in Ukraine, known for its strong engineering, cryptography, and cybersecurity culture.
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