Without them, each chain would remain a siloed economy, stifling the growth of DeFi and NFTs. Bridges enable users to, say, deposit ETH on Ethereum and withdraw an equivalent wrapped version (wETH) on Polygon for cheaper transactions. In the sprawling universe of blockchain technology, cross-chain bridges serve as vital conduits, allowing digital assets to flow seamlessly between isolated networks like Ethereum, Solana, and Binance Smart Chain.
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These bridges unlock liquidity, enable DeFi innovations, and power everything from cross-chain swaps to enterprise settlements. But with great connectivity comes great risk: hackers have siphoned off over $2.8 billion from bridges since 2022, making them one of the juiciest targets in crypto. As the multi-chain ecosystem matures — with $55 billion in total value locked (TVL) across bridges in 2025 — these vulnerabilities aren’t just historical footnotes; they’re ongoing threats that could undermine trust in Web3 interoperability. This article breaks down how bridges operate, the sneaky ways they’re exploited, real-world horror stories, and strategies to lock down the future.
At their core, cross-chain bridges are decentralized applications (dApps) that act like interstellar portals for tokens and data, bridging blockchains that were never designed to talk to each other. Essentially, a cross-chain bridge is a technology that allows communication between two separate blockchain networks, such as transferring and swapping assets, calling functions in contracts from other blockchains, and more. Bridges, in other words, enable users to transfer assets from one network to another. For example, if you have Bitcoin and want to spend it like Ethereum, you can do so via the bridge.
This process relies on trust-minimized mechanisms like Merkle proofs or multi-signature (multisig) approvals to verify transactions without a central authority. The magic happens through smart contracts on both chains:
There will undoubtedly be more opportunities for users to use bridges as the number of different blockchains grows. However, if you are unfamiliar with the characteristics of each bridge, you may be exposed to unexpected risks, so use them with caution.
Bridges aren’t monolithic fortresses; they’re patchwork systems blending on-chain code, off-chain validators, and human oversight. Exploits often target these seams, exploiting logic flaws, human error, or design oversights. Drawing from security analyses, here are seven key vulnerabilities — and how attackers weaponize them.
With all of these major hacks occurring so frequently and in such a short period of time, it should be obvious that security is desperately needed. I’ll go over the most common bridge attacks and provide a list of useful resources to help you protect yourself from potential problems!
In 2023, custodian and communicator attacks dominated, with losses exceeding $1 billion.More recent strikes, like Multichain (July 2023, CEO-linked keys) and Orbit Chain (January 2024, 7/10 keys compromised), show the pattern persists: human elements often trump code.
Often, a cross-chain bridge will monitor for deposit events on one blockchain to initiate a transfer to the other. If an attacker can generate a deposit event without making a real deposit or by depositing with a valueless token, then they can withdraw value from the bridge at the other end.
Cross-chain bridges perform validation of a deposit or withdrawal before actually performing any transfers. There have been many instances in the past where lack of proper validation of signature leads to millions of dollars hacks. Recently BSC chain was attacked because of a similar bug and a total of 576 Million was withdrawn by hackers.
It is important to have access control validations on critical functions that execute actions like modifying the owner, transfer of funds and tokens, pausing and unpausing the contracts, etc.
Some cross-chain bridges have a set of validators that vote whether or not to approve a particular transfer. If the attacker controls most of these validators, they can approve fake and malicious transfers. This is what happened to these validators in the Ronin Network hack, where the attacker took over 5 of the bridge’s 9 validators.
If the admin key of the smart contract is leaked, all the funds and operation of the smart contract will be at great risk. Recently, the Harmony bridge was exploited via the theft of two private keys. The attack resulted in a theft of roughly $100 million in various cryptocurrencies.
Cross-chain bridges embody crypto’s promise of boundless connectivity, but their hacks reveal a harsh truth: innovation outpaces security at our peril. From Ronin’s validator fiasco to Wormhole’s code slip, these breaches have cost billions and eroded confidence. Yet, as 2025 unfolds, emerging standards — deeper audits, decentralized guardians, and proactive limits — signal a turning point. For builders and users alike, the lesson is clear: treat bridges not as given infrastructure, but as battlegrounds demanding vigilance. In a truly interoperable future, the strongest chains won’t be the richest — they’ll be the smartest.
If we finally want to give people the opportunity to be their own bank, we must realize that in this case, people must be able to replace all those services and actions for which traditional banks get money!
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How Cross-Chain Bridges are Hacked? was originally published in Coinmonks on Medium, where people are continuing the conversation by highlighting and responding to this story.
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