Crypto Bridges: Why Cross-Chain Transfers Keep Getting Hacked

If you have ever moved a token from Ethereum to Solana, or from a main chain to a cheaper Layer 2, you have used a crypto bridge — often without thinking about where your coins actually went. That single, invisible step is now the most dangerous place in all of crypto. A crypto bridge hack is not a rare freak event; cross-chain bridges have leaked more money than almost any other part of decentralised finance, with security firms tallying well over $2 billion drained from them. This guide explains, in plain English, how bridges work, why they keep getting hacked, and the handful of checks that separate a careful user from a headline.

What a crypto bridge actually is (and why you would use one)

A blockchain is a closed world. Bitcoin does not know that Ethereum exists; Ethereum cannot see balances on Solana. Each chain keeps its own ledger and has no native way to send an asset to a different chain. A crypto bridge is the software that fakes a connection between two chains that were never designed to talk to each other.

You reach for a bridge for very ordinary reasons. Fees on the Ethereum main chain spike, so you move funds to a Layer 2 like Arbitrum or Base to trade cheaply. A new lending market only exists on one chain, so you bridge stablecoins across to use it. Or an app you want lives on a chain where you hold nothing, so you move value in to get started.

Here is the part that surprises most beginners: your coins never actually travel. A bridge does not teleport your ETH to another network. It parks your real asset on the first chain and hands you a stand-in token on the second chain. Understanding that one fact is the key to understanding every bridge hack ever recorded. If you want this foundation built properly rather than pieced together from scattered videos, a structured cryptocurrency course walks through custody, wallets and on-chain risk in the right order.

How a lock-and-mint bridge works, step by step

The most common design is called lock-and-mint, and once you see the four steps, the risk becomes obvious. It is the same pattern used by the bridges behind most of the losses in this article.

Source: bridge design documentation and security research, 2024-2026.

Step one locks your real ETH inside a smart-contract vault. It sits there, untouched, for as long as your bridged position exists. Step two is a group of off-chain validators — sometimes a decentralised set, sometimes a small federation of servers — watching for that deposit and signing off that it is genuine. Step three mints a wrapped token, a synthetic claim worth one unit of the locked asset, on the destination chain. That wrapped token is what you actually hold and trade. To come back, you burn the wrapped token and the vault on Chain A releases your original.

Notice what this creates. Every user's real assets pile up in one vault on the source chain, and the only thing standing between an attacker and that pile is a set of validator keys plus some contract code. The bridge is a bank vault where the whole neighbourhood keeps its savings, guarded by a lock that a handful of people can open. That is the honeypot.

Why crypto bridges keep getting hacked: the honeypot problem

Bridges are attacked more than exchanges, wallets or lending apps for one structural reason: the money and the weak point are in the same place. A trading app might hold user funds, but a bridge holds pooled collateral for an entire second chain, and it advertises exactly where that collateral is. For an attacker, breaking the bridge is not a side quest — it is the whole prize in a single contract.

The numbers make the pattern hard to argue with. Between 2021 and 2022, five bridge exploits alone removed roughly $1.8 billion from the ecosystem. These were not obscure projects; they backed some of the most-used chains and games in crypto at the time.

One detail in that chart is worth pausing on. The Poly Network attacker eventually gave the money back, which is why you will see the loss described as both the biggest and, oddly, not really a loss. The Ronin bridge, which powered the Axie Infinity game, remains the largest theft where the money was gone for good. That is the honeypot problem in one line: the bigger the locked pile, the bigger the target painted on it.

Two ways a bridge breaks: stolen keys versus broken code

Every bridge hack in the chart above falls into one of two buckets. Learning to tell them apart is genuinely useful, because it tells you what a bridge is actually trusting.

Stolen keys: attacking the people, not the program

The Ronin hack is the classic example. Its bridge used nine validators, and any five could approve a withdrawal. Attackers obtained four keys directly, then reached the fifth through a permission that had been granted months earlier during heavy traffic and never revoked. Nobody broke the code; they simply collected enough keys to unlock the vault legitimately. Harmony's Horizon bridge failed the same way, except its threshold was only two of five signatures — an unusually low bar for a vault holding $100 million.

This is exactly why key custody matters so much in crypto, whether you are running a bridge or just holding coins. We go deeper into who controls the keys in our guide to cold wallets versus hot wallets and in why people lose access in our piece on seed phrase security.

Broken code: minting money from nothing

The Wormhole bridge lost around $325 million when an attacker exploited a flaw in how it verified signatures, tricking the contract into minting 120,000 wrapped ETH on Solana with no matching deposit on Ethereum. Nomad was even starker: a routine upgrade accidentally set its trusted security value to zero, which meant the contract treated every message as valid. The result was a chaotic free-for-all where hundreds of ordinary users copied the exploit and drained the bridge in hours. In both cases the wrapped tokens were suddenly backed by nothing, which is the crypto version of a bank run.

What to check before you bridge

You cannot audit a smart contract yourself, and you should not have to. But you can ask a short list of questions that filters out most of the danger. None of this is investment advice — it is basic operational hygiene.

One more habit worth building: do not treat a wrapped token as a place to park money. The whole point of bridging is to use the destination chain and then, ideally, come back. The longer your value sits as a synthetic claim inside someone else's contract, the longer it is exposed to that contract failing. And remember that in India a bridge or swap can be a taxable event, so it pays to understand the rules — we cover them in our explainer on crypto tax in India.

Where to take this next

Crypto bridges are not a scam, and they are not going away — the entire multi-chain world, including the Layer 2 networks we explained in our guide to Layer 2 rollups, depends on them. The lesson is not to avoid bridges forever, but to use them the way a professional does: knowing that your real coins are locked in a vault, knowing who can open that vault, and moving only what you are prepared to expose while it is in transit.

Get the mental model right and bridges stop being a mystery and become just another tool with a known risk. That is the difference between reacting to headlines and actually understanding the machine underneath them.

Frequently Asked Questions

What is a crypto bridge in simple terms?

A crypto bridge is software that lets you move value between two separate blockchains that cannot natively talk to each other. It does this by locking your real asset on the first chain and issuing you a matching wrapped token on the second chain, so your coins effectively appear on the new network without ever leaving the old one.

Why do cross-chain bridges keep getting hacked?

Because a bridge pools everyone's locked collateral in one contract, and it publicly advertises where that collateral sits. That makes it a single, enormous target. Attackers only need to break one of two things — the validator keys that guard the vault or the contract code that verifies deposits — to drain the entire pool.

What was the biggest crypto bridge hack?

The Ronin bridge hack of March 2022, worth over $600 million, is the largest theft where the funds were not recovered. Poly Network lost a similar amount in 2021, but the attacker returned everything. Wormhole ($325M), Nomad ($190M) and Harmony ($100M) round out the most-cited bridge exploits.

Are crypto bridges safe to use in 2026?

Some are far safer than others. Bridges with large independent validator sets, audited and unchanged code, and a long track record carry less risk than new or thinly-secured ones. Bridges are a normal part of using multiple chains, but you should treat every transfer as an exposure and move only what you can afford to have at risk in transit.

Is bridging crypto taxable in India?

It can be. Converting or swapping one crypto asset for another is generally treated as a taxable transfer under India's virtual digital asset rules, which apply a flat 30% tax on gains plus 1% TDS on transactions. Because bridging often involves a swap into a wrapped token, keep records and check the current rules before assuming a transfer is tax-free.

Disclaimer: This article is for educational purposes only and does not constitute investment advice, and it does not endorse any specific bridge, exchange or product. Markets carry risk — please do your own research or consult a qualified financial professional before investing. NIFM provides training and exam preparation; certification exams conducted by regulatory or professional bodies are administered by those bodies independently.