What Is a Blockchain Bridge and Why Are They the Most Hacked Thing in DeFi?

By Chanuka Geekiyanage Jun 19, 2026

Blockchain bridges let you move assets between separate networks like Ethereum, Solana, Arbitrum, and BNB Chain. The core decision you face is this: which bridge should you trust with your funds, and is the risk worth the yield or access you gain on the other side? Wrong answers have cost users hundreds of millions of dollars in a single transaction. This article helps you evaluate bridges, compare your options, and avoid the mistakes that lead to permanent loss.

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Why Bridges Exist and When You Actually Need One

Blockchains do not communicate natively. Ethereum cannot read Solana's state, and BNB Chain cannot verify an Arbitrum transaction. This isolation is intentional because it preserves each chain's security model, but it creates a real problem for users who want to access yield on Arbitrum, trade on a Solana DEX, or farm stablecoins on Polygon without selling their ETH.

Bridges solve this by locking your token on the source chain and minting a wrapped version on the destination chain. When you return, the wrapped token is burned, and the original is released.

You need a bridge when:

Ethereum gas fees make small transactions uneconomical, and you want to move to Arbitrum or Polygon
A specific yield opportunity, lending protocol, or DEX only exists on one chain
You are arbitrage pricing for the same asset across chains

If you are not doing one of these three things, bridging adds risk with no clear benefit.

Trusted vs. Trustless Bridges: Which Model Should You Use?

The design of a bridge determines where risk concentrates. There are two models, and choosing between them is the first real decision you make before bridging.

Feature	Trusted Bridges	Trustless Bridges
Control	Company or multisig	Smart contracts or validators
Speed	Generally faster	Sometimes slower
Security Risk	Operator honesty and key management	Smart contract code quality
Transparency	Low	High
Examples	Exchange bridges, Binance Bridge	Across Protocol, Stargate, Hop Protocol

Trusted bridges concentrate risk in human operators. If the private keys are stolen or the operator acts dishonestly, the funds are gone. Trustless bridges shift risk to code. If the smart contract has a bug, attackers exploit it automatically and without warning.

Neither model is safe by default. Trustless bridges with unaudited or complex code can be more dangerous than a trusted bridge run by a reputable team with strong operational security.

Why Bridges Are the Biggest Target in DeFi

Bridges hold enormous amounts of locked assets in a single smart contract. Every user who bridges ETH from Ethereum to Arbitrum adds to that pool. At peak usage, major bridges hold hundreds of millions of dollars, sometimes billions, in a single location.

Three factors make bridges uniquely vulnerable:

Concentrated liquidity: A single exploit drains every user's funds at once, not just one wallet
Cross-chain complexity: Bridge code must handle multiple token standards, validator communication, and edge cases across chains simultaneously, creating more surfaces for bugs
Validator dependencies: Many bridges rely on a small validator set to confirm transactions, and compromising enough validators gives an attacker full approval rights over withdrawals

No other category in DeFi combines these three factors at the same scale.

The Three Biggest Bridge Hacks and What Actually Went Wrong

These are not theoretical risks. The following three exploits happened within months of each other and collectively drained over $1 billion from real users.

Bridge	Year	Amount Stolen	Root Cause
Ronin (Axie Infinity)	2022	~$620M	Validator compromise (5 of 9 validators taken)
Wormhole (Solana-Ethereum)	2022	~$320M	Smart contract signature verification bug
Harmony Horizon	2022	~$100M	Private key theft (only 2 keys required to authorize withdrawals)

Ronin: The bridge used 9 validators but only required 5 to approve a transaction. Attackers compromised 5, including one held by a single third-party partner. They approved fraudulent withdrawals, and the theft went undetected for nearly a week.

Wormhole: Attackers found a flaw in how the bridge verified transaction signatures on Solana. They exploited it to mint 120,000 wrapped ETH (wETH) without locking any real collateral, effectively creating money from nothing.

Harmony Horizon: This bridge required only 2 private keys to authorize any withdrawal. Once attackers obtained both keys through targeted theft, no exploit was needed. They simply signed and submitted legitimate-looking transactions.

The pattern is consistent: small validator sets, insufficient key management, and unaudited contract logic each created a single point of failure that wiped out the entire bridge.

How to Evaluate a Bridge Before Using It

Experienced DeFi users do not just use the first bridge they find. They check specific criteria before moving funds. If you want to learn how to bridge assets safely between chains for yield opportunities, this is the framework that matters.

Ask these questions before bridging:

Has the contract been audited? Check who audited it, when, and whether findings were resolved. Audits from Zellic, Trail of Bits, or OpenZeppelin carry more weight than those from unknown firms.
How many validators secure the bridge? A bridge with 5 to 9 validators is a centralization risk. Bridges like Across Protocol use optimistic verification with a large decentralized relayer network.
What is the TVL, and how long has it held? High TVL held over 12 or more months without incident is a meaningful signal. A new bridge with $500M in TVL and no audit history is dangerous.
What is the withdrawal delay? Optimistic bridges like Hop Protocol introduce a challenge window (typically 7 days) to allow fraud detection. Instant bridges carry more counterparty risk.
Is the smart contract upgradeable? Upgradeable contracts give developers the ability to change logic after deployment, which also means a compromised admin key can drain the bridge.

Top Bridge Protocols Compared

These are the bridges most active DeFi users actually use in 2024, with specific tradeoffs:

Stargate Finance (built on LayerZero): Uses a unified liquidity model, meaning there are no wrapped tokens. You receive native assets on the destination chain. It supports Ethereum, Arbitrum, Optimism, BNB Chain, Avalanche, and Polygon. The tradeoff is reliance on LayerZero's messaging layer, which has its own security assumptions.

Across Protocol: Uses a system of relayers who front liquidity and get reimbursed from the source chain after verification. It is fast (often under a minute) and uses a decentralized relayer network. It is well-audited and one of the more trust-minimized options for EVM chains.

Hop Protocol: Designed for EVM Layer 2 bridges specifically. It uses bonded relayers and an optimistic verification window. Good for moving assets between Ethereum, Arbitrum, Optimism, and Polygon with a strong security track record.

Wormhole: Connects non-EVM chains like Solana and Sui with EVM chains. Higher complexity, larger attack surface, and a history of one of the largest exploits in DeFi. Better for users who specifically need Solana access than for general EVM-to-EVM bridging.

For most EVM users, Across or Stargate are the stronger defaults. Wormhole makes sense only when you need cross-chain access to Solana or non-EVM ecosystems and cannot find another path.

Where Bridge Security Is Heading

The industry is actively building toward better security models. Three approaches are showing the most practical progress:

Zero-knowledge proofs (ZK bridges): These allow one chain to mathematically verify the state of another without trusting any validator to report it honestly. zkBridge and similar projects remove human trust from the verification layer entirely.
Light client bridges: Instead of trusting validators, these bridges directly verify the consensus data of the source chain. They check the chain itself, not a third party's report of it.
Decentralized validator networks: Moving from 5 or 9 validators to hundreds or thousands of independent operators makes compromise exponentially more expensive. This is already deployed in mature bridges and is the most practical near-term improvement.

These are not theoretical. ZK-based verification is already in production on several bridges, and cross-chain bridge security is one of the most actively funded research areas in DeFi infrastructure today.

Conclusion

Bridges are a necessary DeFi infrastructure, but they carry risks that no other protocol category matches at scale. The decision is not whether to use bridges, but which ones are safe enough for your specific use case and how much exposure you want to take on. Stick to audited, high-TVL bridges with decentralized validator sets. Avoid new bridges with large TVL but short track records. Always verify that the bridge you are using has had an independent security audit from a credible firm before moving significant capital across chains.

FAQs

1. What is a blockchain bridge in simple terms?

A blockchain bridge connects two separate blockchains so that assets can move between them. It locks your token on the original chain and creates a matching version on the destination chain.

2. Why are blockchain bridges so frequently hacked?

Bridges hold massive pools of locked assets in a single smart contract, making them extremely high-value targets. Their cross-chain complexity also creates more attack surfaces than most DeFi protocols.

3. Are blockchain bridges safe to use?

Well-audited bridges with large validator sets and long track records (like Across or Stargate) carry manageable risk. New or under-audited bridges carry substantially higher risk regardless of their TVL.

4. What is a wrapped token in a bridge?

A wrapped token is a synthetic representation of an asset on a different chain, backed by the original token locked in the bridge contract. It functions like the original asset on the destination chain but carries the bridge's smart contract risk.

5. What bridge should a beginner use?

Across Protocol and Stargate Finance are both strong choices for EVM-to-EVM bridging because they are well-audited, widely used, and backed by decentralized infrastructure. Avoid bridging to unfamiliar chains or using obscure bridges just for higher yields.

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About the Author: Chanuka Geekiyanage

Chanuka is a content writer, editor and contributor at Panaprium, specializing in long-form editorial articles. He conducts in-depth research and produces well-structured, carefully edited content with a strong focus on clarity, SEO best practices, and consistent formatting. His work spans lifestyle, fashion, wellness, and technical topics, and all articles are reviewed and refined to meet Panaprium’s editorial standards.

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