Crypto Bridge Hacks: Why Cross-Chain Bridges Are a Top Attack Vector

Crypto bridge hacks have become some of the most notable sources of exploits in recent years. As users increasingly buy crypto or move funds between chains using crypto onramp services, bridges have quietly become the riskiest part of the transaction lifecycle.

Cross-chain bridges are the infrastructure that allows assets to move between different blockchains. While bridges are essential for a multi-chain future, they have become the most exploited vulnerability in crypto. Bridge exploits accounted for 69% of funds stolen in crypto-related hacks in 2022, with approximately $1.3 billion lost in thirteen separate bridge attacks during that year alone.

Bridge Hacks Report 2022. Source: CNBC

This article examines why cross-chain bridges are such attractive targets for hackers, breaks down the most devastating bridge attacks, and provides practical guidance on how to use bridges more safely.

What Are Cross-Chain Bridges and Why Do We Need Them?

The Multi-Chain Reality

The crypto ecosystem consists of multiple blockchains, including Ethereum, Binance Smart Chain, Solana, Avalanche, and dozens of others that don’t naturally communicate. Each blockchain operates as an independent network with its own consensus mechanism, token standards, and transaction processing. Bridges solve this interoperability problem by allowing assets to move between chains, enabling users to access different DeFi ecosystems, NFT marketplaces, and blockchain applications.

How Bridges Work

The basic mechanics of a bridge involve locking tokens on one chain and minting equivalent wrapped tokens on another chain. When you want to move Ethereum from the Ethereum mainnet to Solana, you send your ETH to a bridge contract where it is locked as collateral. The bridge then mints an equivalent amount of wrapped ETH on Solana that represents a claim on your original tokens. When you bridge back, the wrapped tokens are burned, and the original tokens are unlocked from the contract.

This process requires complex smart contracts and validation mechanisms to ensure that wrapped tokens are always backed one-to-one by the underlying assets. The bridge must verify transactions on both chains, coordinate between different consensus mechanisms, and manage the security of potentially hundreds of millions of dollars in locked collateral.

The Value Honeypot

Bridges hold massive amounts of locked value in smart contracts, making them incredibly attractive targets for hackers. Unlike centralised exchanges that can freeze funds or reverse transactions, bridge exploits are often irreversible once assets are moved. As one analyst noted, as more value flows across these bridges, they become more attractive to hackers because bridge funds could be held in a smart contract or centralised custodian, creating a central storage point which becomes the target.

The Anatomy of Bridge Attacks

Smart Contract Vulnerabilities

Flaws in the bridge smart contract code can allow attackers to mint unlimited tokens or drain locked funds. The complexity of bridge contracts makes them particularly difficult to secure. Bridge contracts must handle cross-chain messaging, signature verification, proof validation, and token minting or burning, all while maintaining security across multiple blockchain environments. A single bug in any of these components can lead to catastrophic losses.

Validator Compromises

Many bridges rely on validators or multisig signers responsible for authorising cross-chain transactions. When hackers compromise these validators, they gain control over the bridge’s core security mechanism. The Harmony Horizon Bridge hack was made possible because hackers only needed to compromise two out of five validator accounts to obtain the passwords necessary for withdrawing funds. This centralisation in bridge security creates dangerous single points of failure.

The Biggest Bridge Hacks in History

Poly Network: Over $600 Million

In August 2021, the Poly Network was attacked by anonymous hackers who transferred over $610 million in digital cryptocurrency. The attack exploited a vulnerability in smart contract interactions between the protocol’s cross-chain messaging system.

According to analysis, the hacker exploited relationships between the EthCrossChainManager and EthCrossChainData contracts. By sending specially formatted commands, the attacker reassigned the keeper role to their own address, allowing them to drain value from the protocol at will. The stolen funds were distributed across Ethereum, Binance Smart Chain, and Polygon blockchains.

PolyNetwork hack. Source: Chainanalysis

In an unusual twist, the hacker returned virtually all the funds over the following fifteen days, claiming through messages embedded in transactions that they did it “for fun” and to expose vulnerabilities. Poly Network dubbed the attacker “Mr White Hat” and offered a five-hundred-thousand-dollar bounty, though this angered security professionals who worried it might set a precedent for criminals to whitewash their actions.

Wormhole Bridge: Over $320 Million

In February 2022, Wormhole, a token bridge between Ethereum and Solana, was exploited for approximately $325 million worth of 120,000 wrapped ETH. The attacker exploited a signature verification vulnerability to mint tokens without providing collateral.

The technical analysis revealed that the hacker created a fake validator action approval with a forged signature that bypassed verification checks. The vulnerability stemmed from the use of a deprecated, insecure function that failed to perform proper signature verification. Before the attack, the hacker received 0.94 ETH from Tornado Cash to pay for gas fees, demonstrating planning.

The exploit was particularly serious because it meant $325 million worth of wrapped ETH on Solana was temporarily unbacked. If this hadn’t been resolved, platforms accepting wrapped ETH as collateral could have become insolvent, potentially crashing the Solana ecosystem. Jump Trading, Wormhole’s parent company, stepped in to replace the stolen ETH and make users whole, preventing a catastrophic systemic failure. For users who want to quickly swap crypto between chains, Wormhole was a popular, but ultimately risky, choice.

BNB Chain Bridge: Over $580 Million

In October 2022, the BSC Token Hub bridge was exploited for approximately $586 million when hackers withdrew two million BNB tokens. The attack exploited a proof verification flaw in the bridge’s smart contract that allowed hackers to forge transactions.

According to a detailed analysis, the attacker exploited a bug in the IAVL Merkle tree implementation used by the bridge. By forging a Merkle proof, the attacker tricked the system into accepting fraudulent transactions that minted BNB tokens without legitimate backing.

However, BNB Chain validators responded swiftly, temporarily suspending the blockchain approximately 90 minutes after the initial exploit. This unprecedented action prevented the attacker from moving most of the stolen funds off-chain. Ultimately, only about $110 million escaped before the chain was halted, with the remaining $400 million frozen. Tether also blacklisted the attacker’s addresses, freezing approximately $7 million in USDT.

Why Bridges Are So Vulnerable

Complexity Breeds Bugs

Bridges are among the most complex smart contracts in crypto, requiring coordination between multiple chains, oracles, and validators. Each additional component increases the attack surface. As security researchers have noted, bridges are mainly experimental, and the technology hasn’t had time to mature, meaning vulnerabilities and novel attack vectors continue to be discovered.

A bridge must handle cross-chain messaging protocols, cryptographic signature verification across different standards, proof generation and validation, token minting and burning mechanisms, and coordination between different consensus systems. Each of these elements represents potential vulnerabilities that attackers can exploit.

Centralization Trade-offs

Many bridges rely on small sets of validators or multisig wallets for security, creating centralization risks that contradict crypto’s decentralized ethos. The Ronin hack demonstrated how a bridge with only nine validators could be compromised when an attacker gained control of just five. Even bridges with more validators face risks if those validators are compromised through social engineering, key theft, or coordinated attacks. A secure crypto wallet is the first line of defence, but the bridge itself remains a weak point.

Immature Technology

Cross-chain bridge technology is still relatively new and experimental, with security best practices still being discovered through expensive failures. Recent analysis showed that compromised keys were the biggest threat in 2023, representing nearly half of all financial losses despite accounting for just 6.3% of security incidents.

How to Use Bridges More Safely

Choose Established Bridges

Use well-audited bridges with proven track records and significant total value locked. While this isn’t a guarantee of security, bridges such as Thorchain, Avalanche bridge, and Polygon bridge have operated successfully for years and processed billions in transactions. This makes them generally more trustworthy than newly launched protocols. Research the bridge’s history, security practices, and any past incidents.

Minimize Bridge Exposure

Bridge only what you need and avoid leaving assets on destination chains longer than necessary. The longer your assets sit in a bridge contract or on the destination chain, the more exposure you have to potential exploits. Consider breaking large transfers into smaller amounts to reduce risk concentration.

Check for Audits

Verify that a bridge has been audited by reputable security firms before using it. Look for publicly available audit reports from well-known firms like Trail of Bits, CertiK, OpenZeppelin, or Consensys Diligence. However, remember that even audited bridges can be exploited if new vulnerabilities are discovered or if audits miss critical issues.

Use Insurance Options

Consider bridge insurance protocols that can provide some protection against bridge exploits. Services like Nexus Mutual and InsurAce offer coverage for smart contract failures, though policies have limitations and exclusions. Review coverage terms carefully to understand what is and isn’t protected.

Stay Informed

Follow bridge protocol announcements and security researchers who often identify vulnerabilities before they’re exploited. Monitor bridge protocol Twitter accounts, Discord channels, and security-focused accounts that report on emerging threats. If you learn of a potential vulnerability in a bridge you’re using, withdraw assets immediately and wait for the issue to be resolved. This is why many institutional users rely on a trusted crypto banking application for greater security oversight.

Conclusion

Bridges are the weakest link in crypto infrastructure. Their complexity creates extensive attack surfaces, centralization trade-offs undermine security, massive economic incentives attract sophisticated attackers, and immature technology means vulnerabilities continue to be discovered through costly exploits.

The path forward requires better security standards before bridges can be truly safe. This includes more thorough auditing processes, decreased reliance on small validator sets, improved cryptographic verification mechanisms, better monitoring and emergency response capabilities, and more mature cross-chain communication protocols.

Security is our top priority at Digitap. While we support multi-chain asset management, we implement the highest security standards to protect your funds. Experience peace of mind with institutional-grade security. Join Digitap today.

FAQ

What is a cross-chain bridge?

A cross-chain bridge is a protocol or application that enables the transfer of tokens, assets, or data between different blockchain networks, which are otherwise isolated due to unique rules and standards.

Why are bridges hacked so often?

Bridges are frequent hack targets because they hold massive locked value as liquidity hubs, creating high-reward incentives for attackers, with over $2 billion stolen in 2022 alone from exploits like Ronin, Wormhole, and BNB Chain

Can I get my money back if a bridge is hacked?

Recovery chances vary: some projects reimburse users fully, like Wormhole (Jump Trading restored $320M) or Ronin (Sky Mavis covered $624M), often via insurance, reserves, or backers.

Which bridges are the safest to use?

The safest cross-chain bridges in 2025 include Symbiosis Finance, Stargate (powered by LayerZero), deBridge, and THORChain.

Are there alternatives to using bridges?

Alternatives to using bridges are Layer 2 rollups, such as Arbitrum, which scale transactions within a single blockchain ecosystem, removing cross-chain risks.