Dmytro Matviiv
CEO HackenProof

While most people recognize blockchains for their role in facilitating digital currencies like Bitcoin and Ethereum, there exists an intricate system working silently in the backdrop, enabling seamless integration between these disparate blockchains.

These are known as ‘bridges’. Just as a physical bridge connects two lands, in the blockchain realm, bridges provide a conduit between different blockchains. However, just as a bridge’s stability is paramount in the real world, in the blockchain sphere, the emphasis on security for these bridges cannot be understated.

Understanding Blockchain Bridges

Defining Blockchain Bridge and its Purpose:

At its core, a blockchain bridge serves as a link, transferring data and value between two blockchains. This could be between two public blockchains, between a public and a private blockchain, or even between two private blockchains.

The fundamental purpose is to overcome the otherwise isolated ecosystems of individual blockchains, offering a way to leverage the unique advantages of multiple systems in a cohesive manner.

Differentiating Between Types of Bridges

There are several different types of blockchain bridges, each with its own advantages and disadvantages. Some of the most common types of blockchain bridges include:

  • Sidechains: Sidechains are separate blockchains that are linked to a main blockchain. They can be used to transfer assets between different blockchains, and they can also be used to execute smart contracts. Sidechains are often more scalable and efficient than main blockchains, but they can also be less secure.
  • Plasma bridges: Plasma bridges are a type of sidechain that uses a technique called “rollups” to batch transactions together and submit them to the main blockchain in a single block. This makes plasma bridges very scalable, but it also introduces a small amount of centralization.
  • Hashlock bridges: Hashlock bridges use a cryptographic technique called “hashlocks” to lock assets on one blockchain and unlock them on another blockchain. This makes hashlock bridges very secure, but they can also be slow and expensive.
  • Trusted bridges: Trusted bridges are centralized bridges that rely on a trusted third party to facilitate transactions between different blockchains. This makes trusted bridges very easy to use but also introduces a single point of failure.
  • Trustless bridges: Trustless bridges are decentralized bridges that do not rely on a trusted third party. This makes trustless bridges very secure, but they can also be more complex to use.

The best type of blockchain bridge for a particular application will depend on a number of factors, such as the security requirements, the scalability requirements, and the cost.

With hundreds of blockchains in existence, each with its unique functionalities and advantages, the ability for these systems to communicate and collaborate is essential.

Blockchain Bridges risks and vulnerabilities

These are just some of the security risks associated with blockchain bridges. It is important to be aware of these risks when using blockchain bridges, and to take steps to mitigate them.

Contract Bugs:

Blockchain bridges largely depend on smart contracts to facilitate seamless transactions between different networks. However, like any code, smart contracts can contain bugs. Simple mistakes in the contract code can inadvertently introduce vulnerabilities, making them susceptible to exploitation. For instance, the Parity Multisig Wallet Bug in 2017 resulted from a simple contract bug, leading to the freezing of 513,774.16 Ethereum, which was worth hundreds of millions of dollars.

Oracle Manipulation:

Oracles are third-party services that feed real-world data into smart contracts. Given that bridges often rely on external data to operate, oracles play a pivotal role. However, since oracles act as an intermediary between the blockchain and the real world, they become potential points of manipulation. Malicious actors can feed oracles false data, which in turn affects the outcome of smart contracts. This deceptive practice can lead to financial losses or false readings, compromising the bridge’s reliability.

Centralization Risks:

While blockchain’s core philosophy revolves around decentralization, certain bridge models can lean towards centralized control. Centralized bridges, operated by a singular entity or a consortium, might offer speed and efficiency but come at a grave risk. Centralized points can be targets for hacks, and there’s always the potential risk of collusion or fraud by the controlling party, compromising the security and transparency that blockchain promises.

Economic Attacks:

Smart contracts in bridges, especially those that deal with lending or financial derivatives, can be susceptible to economic attacks. One glaring example is flash loan attacks. Here, malicious actors borrow funds without collateral, manipulate the market in their favor, and repay the loan in a single transaction, walking away with hefty profits. Such attacks can destabilize bridge protocols, leading to significant financial implications for users and stakeholders.

Denial of Service (DoS) Attacks:

A Denial of Service (DoS) attack aims to disrupt a network’s regular functioning by overwhelming it with a flood of illegitimate requests, rendering the system inoperable. In the context of blockchain bridges, a successful DoS attack can halt cross-chain operations, cause financial losses, and erode trust in the bridge’s capabilities.

Reentrancy Attacks:

A reentrancy attack occurs when, during the execution of a function, an external call is made, and the state of the contract has not yet been updated. This allows the attacker to reenter and execute the function multiple times in a single transaction. In the context of bridges, this can lead to funds being illicitly withdrawn multiple times, causing substantial losses. The infamous 2016 DAO attack on Ethereum, which resulted in the theft of 3.6 million Ether, was a type of reentrancy attack.

Mitigation Strategies

Rigorous Testing and Auditing:

  • Before deploying any blockchain bridge, it’s crucial to subject the code to meticulous testing. This ensures the identification and rectification of potential vulnerabilities. In addition, third-party professional auditing firms should be engaged to audit the bridge’s code.
  • These firms bring a fresh perspective and expertise, often uncovering vulnerabilities that might be overlooked during internal testing. By collaborating with renowned audit firms, blockchain projects can enhance their credibility and assure users of the bridge’s security.

Decentralization of Control:

  • Centralized control is one of the significant risks associated with blockchain bridges. By embracing a decentralized model, where control and decision-making are distributed, the risks associated with a single point of failure are mitigated.
  • Trustless bridge models, such as those utilizing smart contracts or multi-party computations, are exemplary in distributing control, ensuring that no single entity can compromise the bridge’s integrity.

Robust Oracle Mechanisms:

  • Securing the data input sources – oracles – is paramount. One way to enhance oracle security is by using decentralized oracle networks, where data is sourced from multiple points, and a consensus mechanism is employed to validate the authenticity of data.
  • Chainlink’s Threshold Signatures, for instance, provide a system where multiple oracles validate data before it’s fed into the smart contract, making manipulation exponentially harder.

Economic Incentive Structures:

  • By designing a bridge with proper economic incentives, malicious actors can be deterred from exploiting the system. If the cost of attacking the bridge is higher than the potential gain, attackers are less likely to target it.
  • Implementing staking, where entities need to lock up a certain amount of funds to participate, is one such measure. Those acting dishonestly can then face penalties, ensuring bridge integrity.

Time Locks and Multi-Signatures:

  • Time locks ensure that a transaction is executed only after a specified time, providing a window to identify and counteract suspicious activities. Multi-signatures, on the other hand, require multiple parties to sign off on a transaction before it’s processed.
  • Combining these can significantly enhance the security of bridge transactions, ensuring that malicious activities are either delayed or need collaboration from multiple trusted entities to proceed.

Bug Bounty Programs

Finally, running an active bug bounty program can incentivize the identification and reporting of potential security vulnerabilities. By rewarding those who find and disclose such issues responsibly, blockchain projects can add an extra layer of security review, leveraging the collective power of the community to help secure their platforms.


As the digital landscape continues to evolve, blockchain bridges stand out as vital components that amplify the potential and versatility of decentralized ecosystems. They provide a medium for disparate blockchains to interconnect, share data, and value, thus embodying the very essence of collaboration in a decentralized setting.

Security plays an essential role in decentralized projects, as people should be confident in their assets. By taking a proactive and comprehensive approach to security, blockchain projects can safeguard their networks against threats and create a more secure and trustworthy ecosystem for their users.

Want to know more about comprehensive approach to security and bug bounty programs? Get in touch to request a demo with our team today!