Overcoming Reentrancy Attacks: Security Best Practices on NEAR Protocol

Anton Ioffe - March 27th 2024 - 7 minutes read

In the ever-evolving landscape of blockchain technology, the NEAR Protocol has emerged as a beacon of innovation and efficiency. However, even the most fortified bastions are not immune to the cunning strategies of cyber adversaries, among which reentrancy attacks pose a formidable threat. This comprehensive guide ventures deep into the anatomy of reentrancy attacks within the blockchain ecosystem, particularly focusing on their impact and exploitation mechanisms against the NEAR Protocol. We unravel the unique vulnerabilities of NEAR's architecture, presenting a rich tapestry of defensive maneuvers and security best practices designed to fortify smart contracts against these insidious attacks. As we navigate through the labyrinth of mitigation strategies, our journey culminates in a forward-looking exploration of adaptive security measures, ensuring that developers and stakeholders are equipped to anticipate and neutralize future threats. Prepare to embark on a critical exploration that not only educates but empowers the NEAR community to safeguard its digital realm against the specter of reentrancy attacks.

Understanding Reentrancy Attacks in the Blockchain Ecosystem

Reentrancy attacks represent a significant security vulnerability within the blockchain ecosystem, specifically targeting the inherent logic of smart contracts. These attacks occur when an attacker takes advantage of the execution order in smart contracts, especially those that involve external calls to untrusted contracts. In essence, a reentrancy attack is executed by initiating a function in a vulnerable contract and, through an external call, the attacker's contract re-enters the original function before its initial execution is completed. This recursive calling can lead to unexpected behaviors, such as the withdrawal of funds multiple times in a single transaction. The critical point of exploitation is the smart contract's failure to update its state before executing the external call, thereby leaving a window open for attackers to drain funds or manipulate the contract state.

The mechanism of a reentrancy attack hinges on the contract's design that allows for calls to external contracts. This is a common feature in many decentralized applications (DApps) as it enables interaction between various contracts and enhances the functionality of the blockchain ecosystem. However, it also introduces a potential vulnerability. In the process of a reentrancy attack, the attacker’s contract is designed to fallback or receive funds, triggering the fallback function to make another call back to the original function, creating a loop. This vulnerability exploits the synchronous nature of blockchain transactions, where the state changes are not finalized until the end of the transaction, allowing the malicious contract to execute the same function multiple times within a single transaction.

The impact of reentrancy attacks on blockchain platforms and smart contracts is profound, as demonstrated by historical incidents such as the infamous DAO attack on Ethereum. These attacks underscore the critical need for secure coding practices and rigorous security audits in the development phase of smart contracts, particularly for platforms like the NEAR Protocol. Taking such vulnerabilities into consideration is essential for the stability, security, and trust in blockchain technologies and decentralized applications. Despite the structural differences and advancements in blockchain platforms over time, the principle of reentrancy remains a pertinent risk, emphasizing the importance of understanding and guarding against such vulnerabilities in evolving blockchain ecosystems.

Analyzing Reentrancy Vulnerabilities on NEAR Protocol

The NEAR Protocol presents a unique infrastructure in the blockchain ecosystem, designed to enhance scalability and user experience, but it also introduces distinctive challenges in managing reentrancy vulnerabilities. A significant aspect of the NEAR Protocol is its smart contract design patterns, especially concerning its transaction execution flow. Unlike platforms such as Ethereum, where the EVM (Ethereum Virtual Machine) processes transactions linearly, NEAR leverages sharding technology to parallelize transaction processing. This difference in transaction handling could potentially alter the nature of reentrancy vulnerabilities, making it crucial to understand how concurrent execution within shards might expose new vectors for reentrancy attacks, especially if cross-contract calls are not adequately synchronized or checked.

In addition to its unique transaction execution flow, the NEAR Protocol’s approach to state changes and external calls in smart contracts also plays a vital role in its susceptibility to reentrancy attacks. Smart contracts on NEAR are written in AssemblyScript or Rust, which compile to WebAssembly. This programming model requires explicit attention to state management and the sequence of operations. Specifically, the potential for reentrancy vulnerabilities may increase if a contract's state is altered after an external call is made—a practice that NEAR developers are strongly advised against. Considering the atomicity of transactions on NEAR, where operations either fully succeed or fail without state changes, careful structuring of transaction logic is imperative to prevent reentrancy possibilities.

Moreover, the NEAR Protocol incorporates several inherent safeguards aimed at mitigating security risks, including reentrancy attacks. One of these safeguards is the NEAR Runtime, which enforces strict isolation between contract executions, thereby limiting the direct impact of any single execution’s failure. However, while these measures are beneficial, the efficacy of existing safeguards against reentrancy attacks primarily relies on their implementation within the smart contract’s code. Therefore, it is essential for developers to utilize these safeguards effectively and remain vigilant for the unique ways in which reentrancy vulnerabilities could manifest within the NEAR environment, taking into account its specific architectural and operational nuances.

Best Practices for Mitigating Reentrancy Risks on NEAR

One effective defense against reentrancy attacks on the NEAR Protocol is employing the checks-effects-interactions pattern. This strategy dictates the order of operations within a contract function to minimize vulnerabilities: first, validate conditions (checks), then update the contract's state (effects), and finally, interact with other contracts or addresses (interactions). This pattern helps prevent reentrancy by ensuring that all state changes are finalized before any external calls are made, reducing the attacker's ability to exploit state inconsistencies. The primary advantage is the increased security posture it offers; however, its implementation requires meticulous structuring of contract logic, which might be a steep learning curve for developers new to these concepts.

Implementing reentrancy guards is another proactive measure developers can take. These guards are mechanisms that lock the contract's state when a function is being executed, preventing any reentrant calls until the first execution is completed and the state is unlocked. This can be achieved through the use of simple Boolean flags that check whether the function is already running. Pros include a straightforward way to prevent reentrant executions with minimal impact on contract logic. On the downside, care must be taken to ensure that these guards do not inadvertently introduce new vulnerabilities, such as locking the contract in a state where it can't process legitimate calls.

Thorough audits with NEAR-specific tooling offer an additional layer of defense. Automated tools and manual code reviews can detect potential reentrancy vulnerabilities before the smart contract is deployed. While NEAR's environment may differ from Ethereum, principles of secure smart contract development remain consistent, including the avoidance of pitfalls around external calls. The advantage of this approach lies in identifying and addressing vulnerabilities early in the development cycle, which significantly reduces the risk and impact of attacks. However, a comprehensive audit requires deep understanding of both general security practices and NEAR’s ecosystem, making it essential to have access to skilled auditors familiar with the subtleties of the protocol.

Future Outlook and Adaptive Security Strategies

With the threat landscape constantly evolving, the NEAR Protocol and its robust developer community are poised to spearhead innovations in blockchain security against reentrancy and more sophisticated cyber threats. A forward-looking approach involves integrating innovative technologies such as artificial intelligence (AI) and machine learning (ML) for early detection and mitigation of potential security breaches. These technologies have the capacity to analyze patterns and predict attack vectors before they materialize, offering a dynamic layer of defense that evolves with the threat itself. However, the integration of AI and ML raises critical questions: How can we ensure these technologies do not become a double-edged sword, where their predictive capabilities are misused by adversaries to sophisticate their attack methods further?

Community collaboration stands as a cornerstone for adaptive security within the blockchain ecosystem. By fostering a culture of open communication and continuous knowledge sharing, the NEAR Protocol community can leverage collective intelligence to stay ahead of attackers. This collaborative effort not only accelerates the identification and resolution of new vulnerabilities but also promotes the adoption of best practices across the board. Yet, this begs the question: In an open and collaborative environment, how do we balance the need for transparency with the risk of exposing sensitive information that could potentially be leveraged by malicious actors?

Ongoing education and the continuous adaptation of security measures are vital in keeping pace with emergent threats. The blockchain landscape is in a perpetual state of flux, mandating stakeholders to remain vigilant and proactive in updating their knowledge and security protocols. This includes regular updates to smart contracts and DApp interfaces on the NEAR Protocol to address newly discovered vulnerabilities. The quest for a resilient security posture is relentless and requires a commitment to lifelong learning and adaptability. However, it prompts thoughtful contemplation on how to effectively incentivize the communal and individual efforts towards continuous learning and improvement in security practices. In the face of ever-advancing threats, how can the NEAR Protocol community innovate to ensure that education and adaptation processes are not only reactive but also predictive of future security challenges?


This article explores the concept of reentrancy attacks within the NEAR Protocol blockchain ecosystem. It highlights the vulnerabilities and potential impact of these attacks, emphasizing the need for secure coding practices and rigorous security audits. The article discusses specific vulnerabilities within NEAR's architecture and offers best practices for mitigating reentrancy risks, such as employing the checks-effects-interactions pattern and implementing reentrancy guards. The importance of thorough audits and future-oriented adaptive security strategies, including the integration of AI and community collaboration, is also emphasized. Overall, the article aims to educate and empower the NEAR community to safeguard against reentrancy attacks and future security challenges.