Tools for Security Audit and Vulnerability Analysis of Smart Contracts

Smart contracts are an essential component of blockchain technology, and have helped it transcend typical cryptocurrency and financial transactions. But these contracts do come with a few flaws, making it imperative that they go through a security audit. Among the various tools available for this, Slither ranks high.

Blockchain technology has emerged as a revolutionary solution with versatile applications beyond its initial association with cryptocurrencies. Its decentralised and tamper-resistant nature offers a range of real-world use cases that go beyond financial transactions.

With the implementation of smart contracts, the blockchain environment provides high-end and fully secured applications for assorted domains including e-governance, real estate, finance, logistics, and many others. Smart contracts are transforming the real estate industry by automating property transactions. They facilitate seamless and secure buying, selling, and renting of properties, with ownership transfers occurring only when payment conditions are met.

Key use cases and applications of blockchain

Imagine a world where transparency is a given, fraud is rendered nearly impossible, and trust between parties is inherent. That’s the world blockchain technology is shaping.

• Supply chain management: Blockchain provides end-to-end transparency and traceability in supply chains. Each step of a product’s journey can be recorded on the blockchain, ensuring authenticity and preventing fraud. This is particularly important in industries where provenance, such as the origin of luxury goods or food products, is critical. Smart contracts ensure automatic execution of agreements when predefined conditions, such as the arrival of goods at a specified location, are met. This real-time tracking minimises fraud, reduces paperwork, and streamlines logistics processes.
• Decentralised finance (DeFi): Smart contracts have become the foundation of the DeFi movement. They power lending and borrowing platforms, decentralised exchanges (DEXs), automated market makers (AMMs), and yield farming protocols. These applications enable users to engage in financial activities without intermediaries, enhancing transparency, reducing costs, and offering a wide range of financial services.
• Healthcare: Blockchain can securely store and share patients’ medical records across healthcare providers. This ensures data accuracy, privacy, and reduces administrative inefficiencies. Patients have more control over their data, granting access only to authorised parties.
• Voting systems: Blockchain-based voting systems offer secure and transparent elections. Each vote is recorded as a transaction, preventing tampering and ensuring the integrity of the electoral process. This can help enhance voter trust and reduce instances of fraud. Decentralised voting systems use smart contracts to conduct transparent and tamper-resistant elections.
• Digital identity: Blockchain can create self-sovereign identities that users control. This could replace traditional identification methods, allowing individuals to manage and share their personal information securely while reducing identity theft and data breaches.
• Energy trading: Blockchain enables peer-to-peer energy trading, where individuals with solar panels can sell excess energy to their neighbours. This decentralised approach can make energy distribution more efficient and environment-friendly.
• Intellectual property rights: Blockchain can be used to prove ownership and protect intellectual property rights. Digital assets like artwork, music, and patents can be securely registered and tracked on the blockchain, preventing unauthorised use.
• Cross-border payments: Blockchain-based remittance services offer faster, cheaper, and more secure cross-border transactions. Traditional banking intermediaries are bypassed, reducing fees and delays. Smart contracts simplify cross-border transactions by automating currency exchange and payment execution. This eliminates intermediaries, reduces fees, and accelerates the transfer process.
• Gaming and non-fungible tokens: The ability of blockchain to prove ownership has led to the rise of blockchain-based gaming and digital collectibles. Players can truly own in-game assets, and unique digital items can be bought, sold, and traded securely. Smart contracts are at the heart of blockchain-based gaming and NFT platforms to enable the creation, ownership, and trading of unique digital assets.

Smart contracts and decentralised applications

Smart contracts have emerged as a cornerstone of innovation within decentralised applications (DApps). The integration of smart contracts brings a multitude of benefits to various sectors, revolutionising how decentralised applications operate and interact with users.

Smart contracts are self-executing contracts with the terms of the agreement directly written into code. They automatically execute when predefined conditions are met, reducing the need for intermediaries and streamlining processes in areas like real estate, insurance, and legal agreements.

While smart contracts offer numerous advantages, they also come with challenges, including coding vulnerabilities and legal considerations. As the technology evolves, careful planning, code auditing, and integration within a comprehensive DApp ecosystem are vital for harnessing the full potential of smart contracts.

Need for security audit and vulnerability analysis of smart contracts

Smart contracts, while offering immense potential to revolutionise industries, are not immune to vulnerabilities and flaws that can lead to significant financial losses, breaches of privacy, and disruptions of services. Conducting thorough security audits and vulnerability analyses is essential to ensure the integrity and reliability of these self-executing pieces of code. Let’s find out why.

• Immutability of smart contract code: Smart contracts are designed to be immutable once deployed on the blockchain. This means that any errors or vulnerabilities present in the code can’t be easily rectified without deploying a new contract. Thus, a rigorous security audit before deployment is crucial to catch and address potential issues.
• Financial impact: Many smart contracts deal with financial transactions, such as decentralised finance (DeFi) protocols and token sales. Vulnerabilities in such contracts can be exploited by malicious actors to syphon funds or manipulate the contract’s behaviour, resulting in substantial financial losses.
• Economic incentives for hackers: The decentralised nature of blockchain networks and the potential for financial gain make smart contracts attractive targets for hackers. Exploiting vulnerabilities can yield significant rewards, incentivising cybercriminals to search for weaknesses.
• Lack of central authority: Traditional software development benefits from central authorities and regulatory bodies that can enforce security standards. In contrast, the decentralised and permissionless nature of blockchain means that security measures need to be embedded in the code itself.
• Complexity and interconnectedness: Smart contracts can interact with multiple other contracts and external data sources. This complexity increases the attack surface and the likelihood of unforeseen vulnerabilities emerging from interactions between different components.
• Inadequate testing: Smart contracts require specialised testing methodologies. Traditional software testing may not be sufficient due to the unique features of blockchain technology. Security audits help identify issues that might be missed by conventional testing approaches.
• New technology, new risks: Blockchain technology and smart contracts are still relatively new, and security best practices are continually evolving. Conducting regular security audits helps keep up with the latest security standards and practices.
• User trust: Users of decentralised applications rely on the security and reliability of the underlying smart contracts. Any breach or vulnerability can erode trust, causing users to lose confidence in the technology and the services built on it.
• Legal and reputational risks: Security breaches not only result in financial losses but also expose projects to legal liabilities and reputational damage. This can have long-lasting consequences on the success and adoption of the project.
• Preventative approach: A proactive approach to security, through audits and vulnerability assessments, is more cost-effective than attempting to recover from an exploit or breach after it occurs.

In short, security audit and vulnerability analysis of smart contracts is a critical component of responsible blockchain development. It safeguards the integrity of transactions, protects user assets, and upholds the reputation of projects.

There are several free and open source security audit tools available for auditing blockchain smart contracts (Table 1). These tools help identify vulnerabilities and potential security issues in your smart contracts.

Installation and working with Slither for security audit and vulnerability testing

Slither is a powerful and versatile tool that aids in identifying vulnerabilities and improving the security of Ethereum smart contracts. Its features make it an essential component of the development toolkit for those working in the blockchain space.

Slither is an open source tool designed to analyse Ethereum smart contracts for security vulnerabilities and issues. It’s widely used by developers and auditors to ensure the safety and reliability of smart contracts.

Key features of Slither

Slither is like a shield against code vulnerabilities. Let’s delve deeper into some of its key features and witness how it helps secure smart contract development.

Static analysis: Slither performs static analysis on smart contracts, which means it analyses the code without executing it. This helps identify potential vulnerabilities and issues without the need to deploy the contract on the blockchain.

Vulnerability detection: One of Slither’s primary functions is to detect a wide range of vulnerabilities and weaknesses in smart contracts. These vulnerabilities can include issues like reentrancy attacks, unchecked send calls, integer overflows, and more.

Custom rules: Slither allows users to define custom rules and checks that are specific to their project’s requirements. This flexibility enables developers to target specific patterns or issues that might not be covered by default rules.

Integration with build process: It can be integrated into the development workflow, often as part of the continuous integration (CI) pipeline, to automatically analyse contracts whenever changes are made to the codebase. This ensures that potential issues are caught early in the development process.

Interactive reports: Slither generates comprehensive reports that detail the identified vulnerabilities and issues. The reports provide insights into the location of the issue, its severity, and possible solutions. This information assists developers in understanding and fixing the problems.

Gas estimations: For Ethereum smart contracts, gas costs are a critical consideration. Slither provides gas estimations for various execution paths within the contract, helping developers understand the potential gas expenses of their code.

Support for multiple languages: While Slither is mainly designed for Solidity, the primary programming language for Ethereum smart contracts, it also supports other languages that compile to Ethereum bytecode, such as Vyper.

Continuous updates: The tool is actively maintained by the community, which means it receives regular updates to improve its detection capabilities and support the evolving landscape of smart contract security issues.

To install Slither, use pip installer:

pip install slither-analyzer

After completing the installation, you can verify it as follows:

slither --version

Once Slither is successfully installed, it can be used to analyse Solidity smart contracts for security vulnerabilities.

For example, to analyse a Solidity file named ‘MyContract.sol’, you can navigate to its directory and then run:

slither MyContract.sol

Slither will analyse the contract and provide you with a report of any potential security issues it detects.

Let’s say there is a Solidity smart contract named ‘SimpleToken.sol’:

pragma solidity ^0.8.0;

contract SimpleToken {

mapping(address => uint256) public balances;

constructor() {

balances[msg.sender] = 1000;

}

function transfer(address to, uint256 amount) public {

require(balances[msg.sender] >= amount, “Insufficient balance”);

balances[msg.sender] -= amount;

balances[to] += amount;

}

}

To perform an audit using Slither, follow these steps:

• Open a terminal window.
• Navigate to the directory containing your Solidity contract.
• Run Slither on your contract

> slither SimpleToken.sol

Slither will analyse your Solidity code and provide a report on the potential security issues it detects.

Slither static analysis report

Summary :

High : 0

Medium : 0

Low : 0

Informational : 1

Detectors :

UninitializedState : uninitialized state variables

· contracts/SimpleToken.sol : L3 : 3 | SimpleToken | balances

In this example, Slither’s uninitialised state detector detected that the balances mapping is uninitialised in the constructor. The developer of the smart contract should initialise it properly in the constructor to avoid potential issues.

Another example code of Slither for audit of Solidity code is:

pragma solidity ^0.8.0;
contract Fundraiser {
mapping(address => uint256) public balances;

function contribute() public payable {
balances[msg.sender] += msg.value;
}

function withdraw(uint256 amount) public {
require(balances[msg.sender] >= amount, “Insufficient balance”);

balances[msg.sender] -= amount;

(bool success, ) = msg.sender.call{value : amount}(“”);
require(success, “Transfer failed”);

}
}

In the following output, Slither’s ‘UncheckedSend’ detector detected that there is an unchecked use of the call function for sending funds. This can potentially lead to issues if the recipient of the funds is a contract with a fallback function that throws an exception or reverts. It’s recommended to use the transfer function instead of a call to handle fund transfers safely.

Slither static analysis report

Summary :
High : 1
Medium : 0

Low : 0
Informational : 0

Detectors :
UninitializedState : uninitialized state variables

· contracts/Fundraiser.sol : L3 : 3 | Fundraiser | balances
UncheckedSend : usage of unchecked send

· contracts/Fundraiser.sol : L14 : 11 | Fundraiser | call()

With the growing adoption of blockchain across industries, ensuring the robustness and security of smart contracts is crucial. Researchers can explore advanced vulnerability detection methods, automated fingerprinting of vulnerabilities, and integration of AI and machine learning to enhance accuracy. Addressing scalability challenges, real-time monitoring, regulatory compliance, privacy-enhancing techniques, and community engagement through bug bounties are pivotal areas of focus. This will help establish secure and resilient blockchain ecosystems that drive innovation and inspire trust.