Cross-Chain Bridges: What They Are and Why They Keep Getting Hacked
Cross-chain bridges have lost over $2 billion to hacks. UK investors need to understand the risks before moving assets between blockchains.
In August 2022, the Nomad bridge was exploited for $190 million in under an hour. In February 2022, the Wormhole bridge lost $320 million in a single transaction. Ronin Network lost $625 million in March 2022. Cross-chain bridges have been responsible for more stolen funds than any other category of crypto hack.
Yet bridges are essential infrastructure. Without them, the multi-chain world of 2026 — where assets and applications exist across Ethereum, Solana, Bitcoin, and dozens of Layer 2 networks — would be fragmented and unusable. Understanding why bridges are so vulnerable is important for any UK investor moving assets between chains.
What Is a Cross-Chain Bridge?
Different blockchains cannot directly communicate with each other. Bitcoin has no concept of Ethereum tokens. Ethereum cannot natively read Solana’s state. Each chain is an isolated system with its own rules, validators, and assets.
A bridge creates a connection between two chains. The most common approach works like this: you deposit an asset on Chain A. The bridge locks that asset in a smart contract on Chain A. It then mints a wrapped version of that asset on Chain B, which you can use on Chain B’s applications. When you want to move back, you burn the wrapped asset on Chain B and the bridge releases your original asset from the contract on Chain A.
The locked assets on Chain A are the vulnerable point. At peak usage, major bridges hold billions of dollars in locked assets — making them extraordinarily attractive targets.
Why Bridges Are So Hard to Secure
Bridges are complex systems operating across multiple environments simultaneously. A bug in any component — the smart contracts on either chain, the off-chain validators that verify cross-chain messages, the key management systems — can be catastrophic.
The Wormhole hack exploited a signature verification vulnerability. The attacker convinced the bridge that a transaction had been approved when it had not, allowing them to mint 120,000 wrapped ETH — worth $320 million at the time — out of thin air. Jump Crypto, the firm backing Wormhole, replenished the funds within days to maintain confidence in the protocol. Most exploited bridges are not so lucky.
The Nomad hack was even more striking because it did not require sophisticated technical skills. A bug in the contract allowed any arbitrary message to be treated as valid. Once one attacker discovered this, hundreds of copycat attackers joined in, draining the bridge in a chaotic free-for-all that happened in public on the blockchain.
The Ronin hack — the largest single crypto exploit ever at the time — targeted the validator keys rather than the smart contracts. Hackers compromised five of the nine validator nodes that controlled the bridge, giving them the authority to approve fraudulent withdrawals. The hack went undetected for six days.
Types of Bridges and Their Risk Profiles
Trusted bridges rely on a central entity or a small set of validators to verify cross-chain messages. They are simpler to build and typically faster, but they introduce counterparty risk — you are trusting specific parties not to be hacked or act maliciously.
Trustless bridges use cryptographic proofs — typically zero-knowledge proofs — to verify cross-chain messages without relying on any trusted party. They are significantly more secure but technically complex and more expensive to operate. ZK-based bridges from zkSync and StarkWare represent this approach and are widely considered the future of secure bridging.
Liquidity networks take a different approach entirely. Instead of locking and minting, they use pools of liquidity on each chain. When you bridge from Ethereum to Arbitrum, a liquidity provider gives you ETH on Arbitrum immediately and is later reimbursed from your deposit on Ethereum. Hop Protocol and Across use this model. The attack surface is different — smaller smart contracts, less locked value — though not zero.
The State of Bridge Security in 2026
Bridge security has improved substantially since 2022. The industry has responded with more rigorous auditing standards, bug bounty programmes paying millions of dollars for discovered vulnerabilities, and architectural improvements that reduce the size of the attack surface.
Major exploits in 2025 were significantly smaller than the 2022 peaks — tens of millions rather than hundreds of millions — partly because better security and partly because some of the most vulnerable bridge designs have been replaced.
The safest bridges in 2026 are the native bridges of major Layer 2 networks — the official Arbitrum bridge, the official Optimism bridge, the official zkSync bridge. These have had the most rigorous security review and the backing of significant teams and treasuries.
Practical Guidance for UK Investors
Use official bridges for significant amounts. The official bridge of an established Layer 2 network has more security review and incident response capability than third-party aggregators. The user experience is slightly less convenient but the risk reduction is significant.
Check the total value locked before bridging significant sums. A bridge holding $5 billion in locked assets is a larger target than one holding $50 million, but it has also had far more scrutiny and typically has more robust security. New bridges with limited track records and significant TVL are the highest risk combination.
Look for audit reports from reputable firms — Trail of Bits, OpenZeppelin, Certik. Not all audits are equal, and an audit does not guarantee safety, but it is a minimum bar. Avoid bridges that have not been independently audited.
UK investors keep asking whether bridge hacks mean they should avoid cross-chain activity entirely. That is too conservative — bridges are essential for accessing Layer 2 networks where most new DeFi development happens. The answer is to use the right bridges, keep individual bridge exposures limited, and treat any bridge transfer as a risk-bearing activity rather than a routine operation.
This article is for educational purposes only and does not constitute financial advice. Cryptocurrency investments involve significant risk. Always do your own research.
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