L2 cross-chain bridges have been the single biggest security black hole in crypto over the past three years, with cumulative losses topping $2.5 billion. Visit the Binance official site to sidestep most bridge risk by using a centralized exchange instead, download the official Binance app to withdraw straight to an L2 network, and iPhone users should check the iOS installation guide first. The short answer: official L2 bridges (Arbitrum, Optimism, and Base's native bridges) inherit Ethereum mainnet security and have never been hacked; multisig-based "generalized bridges" (Multichain, Wormhole, Ronin, and others) are historically the hardest hit, with losses on a single bridge running into the hundreds of millions of dollars.
Here are the major historical bridge hacks, sorted by amount lost.
| Date | Bridge | Amount Lost | Attack Method |
|---|---|---|---|
| 2022-03 | Ronin Bridge | $625M | Validator private key theft (North Korea's Lazarus) |
| 2022-02 | Wormhole | $325M | Smart contract vulnerability |
| 2023-07 | Multichain | $130M | Insider malfeasance (CEO's death) |
| 2022-08 | Nomad | $190M | Smart contract vulnerability |
| 2022-06 | Harmony Horizon | $100M | Multisig private key theft |
| 2021-08 | Poly Network | $610M | Smart contract vulnerability (returned by white hat) |
| 2022-01 | Qubit | $80M | Contract vulnerability |
| 2024-09 | Penpie/Pendle | $27M | Reentrancy attack |
| 2022-10 | BNB Bridge | $566M | IAVL vulnerability (validators halted the chain in an emergency) |
Add these up and bridges have lost roughly $2.6 billion cumulatively, making them the single largest attack surface in DeFi.
Ronin is the Ethereum sidechain bridge Sky Mavis built for the Axie Infinity game. In March 2022, the North Korean state-sponsored hacking group Lazarus Group used social engineering (a fake job offer) to compromise a Sky Mavis employee's computer, eventually obtaining 5 of the bridge's 9 validator private keys (Ronin's multisig threshold was 5-of-9), and drained 173,600 ETH plus 25.5 million USDC from the bridge contract — roughly $625 million at the time.
The Ronin hack exposed the core risk of "low-threshold multisig" — a 5-of-9 setup looks solid on paper, but full control over the funds only requires 5 stolen keys. After the incident, Sky Mavis raised the multisig threshold to 8-of-11 and deployed on-chain fraud-proof mechanisms.
Between 2022 and 2024, North Korea's Lazarus Group stole roughly $3 billion cumulatively from crypto bridges and exchanges, making it the biggest threat actor in the space.
Wormhole is a major bridge connecting Solana and Ethereum. In February 2022, hackers discovered a flaw in Wormhole's signature verification function — by passing in a forged Sysvar::Instructions account, they could bypass the signature check and mint 120,000 wETH (wrapped ETH), worth $325 million.
Jump Trading, Wormhole's main backer, immediately covered the 120,000 ETH gap from its own reserves to keep the wETH on Solana from becoming unbacked "phantom tokens." This is the largest "VC bailout" event in crypto history.
Afterward, Wormhole completed multiple audits and introduced the Wormhole Guardian Network (19 guardian nodes), but the bridge's underlying architecture hasn't changed — it's still a multisig-plus-smart-contract model, carrying both signature-bypass and contract-bug risk.
Nomad is a bridge built on "optimistic verification." In August 2022, a contract upgrade mistakenly marked a zero hash as a valid root, which meant anyone could forge cross-chain messages and drain the bridge. What made this incident unique was that the attack required no technical skill — ordinary users simply copied the first attacker's transaction, swapped in their own address, and withdrew funds.
Ultimately, more than 300 "distributed attacker" wallets took part, draining $190 million in total. The Nomad team later recovered about $40 million, with most of the rest lost into mixers. The incident cast serious doubt on the "optimistic verification bridge" model.
Multichain (formerly Anyswap) was one of the largest multi-chain bridges from 2021 to 2023, connecting more than 80 chains. In May 2023, Multichain's CEO, Zhaojun, was taken in by Chinese police for questioning, and since the bridge's operating private keys (multisig) were solely controlled by the CEO, bridge operations ground to a halt.
In July 2023, roughly $130 million flowed out of the Multichain bridge contract to unidentified multisig addresses. Multichain announced that its CEO was "unreachable" and that some of the multisig private keys were unaccounted for. By early 2024, Multichain was effectively confirmed dead, with most of the funds unrecoverable.
This is a textbook case of a bridge's "insider malfeasance" risk — there was no technical vulnerability, but the disappearance or misconduct of key operating personnel brought the entire bridge down.
Harmony's Horizon bridge used a 4-of-9 multisig to control funds. In June 2022, hackers used phishing to obtain the private keys of 2 core team members, plus 2 more (also presumably via phishing), giving them 4 signatures in total and letting them drain $100 million from the bridge.
A 4-of-9 multisig is one of the lowest thresholds among cross-chain bridges. After the Harmony incident, industry consensus shifted to "multisig bridge thresholds should be >= N/2 + 2," starting at 5-of-9 and ideally 7-of-11 or 8-of-12.
In August 2021, hackers drained $610 million from the Poly Network cross-chain bridge, the largest bridge hack at the time. But this attacker turned out to be a "white hat" — after succeeding, they contacted the Poly Network team on their own and returned every asset, treating it purely as a "vulnerability demonstration."
Poly Network publicly thanked the hacker and even offered them a role as a security advisor. This dramatic ending made the Poly Network incident one of the most unusual cases in crypto security history. But the underlying flaw (a broken contract permission check) still exposed just how fragile bridge code security can be.
Official L2 bridges (the Arbitrum Bridge, Optimism Bridge, Base Bridge) have never suffered a large-scale attack. There are three reasons for this.
First, their security model doesn't rely on multisig. An official L2 bridge's security is inherited from the Ethereum mainnet — deposits lock assets in a mainnet contract, and withdrawals require either a ZK proof (zkSync, Polygon zkEVM) or a 7-day challenge period (Arbitrum, Optimism).
Second, the code has been deeply audited. Arbitrum's and Optimism's bridge contracts have been audited multiple times by top security firms like Trail of Bits, ConsenSys Diligence, and OpenZeppelin.
Third, the cost of attack is extremely high. Even if a vulnerability is found, an attacker has to evade network-wide monitoring for the entire 7-day challenge period, a far higher bar than attacking a traditional multisig bridge.
| Type | Security Model | Historical Hacks |
|---|---|---|
| Official L2 bridge | Mainnet cryptographic verification | 0 |
| ZK bridge (Across, Polyhedra) | ZK proof | 0 |
| Multisig generalized bridge (Multichain, Wormhole) | N-of-M multisig | Multiple |
| Liquidity pool bridge (Hop, cBridge) | Liquidity + multisig | Occasionally |
Rule one: for large amounts (over $100,000), use only official L2 bridges. Even with the 7-day challenge period, it's still better than taking on the risk of a multisig bridge getting hacked. The official bridges from Arbitrum, Optimism, and Base are the safest option available today.
Rule two: for smaller amounts (under $10,000), third-party bridges are fine. Bridges like Across, Stargate, and Hop are fast and cheap, more than sufficient for everyday small transfers. Just don't leave large amounts parked on a bridge for long.
Rule three: avoid new bridges. Any cross-chain bridge that's been operating for less than a year counts as high risk. Neither the contract's vulnerability surface nor its multisig key security has been thoroughly proven yet.
Rule four: spread usage across bridges. Even among third-party bridges, spread your usage across several (Across, Stargate, Synapse, etc.) rather than relying on one, so a single bridge incident doesn't wipe everything out.
Rule five: routing through a centralized exchange is the safest. For moving funds from Arbitrum to Solana, the safest route is Arbitrum → Binance → Solana. The fee is a bit higher than a direct bridge, but it's the safest option.
Cross-chain bridges face four main attack vectors.
| Vector | Cases | Difficulty to Defend |
|---|---|---|
| Smart contract vulnerability | Wormhole, Nomad, Poly Network | Medium (audits help) |
| Multisig private key theft | Ronin, Harmony | High (social engineering is hard to fully block) |
| Insider malfeasance | Multichain | High (a human problem) |
| Validator misconduct | Some PoS bridges | High (economic incentives) |
Smart contract vulnerabilities can be mitigated through audits and bug bounties, but eliminating them entirely is nearly impossible. Multisig key theft can be reduced through distributed custody and hardware wallets. Insider malfeasance is the hardest problem to solve — as long as a bridge is controlled by a small group of people, there's always a chance of misconduct.
Over the past two years, ZK bridges (like Polyhedra and zkBridge) have started to gain traction. They replace multisig with ZK proofs, turning cross-chain message verification into a fully mathematical process that, in theory, eliminates both multisig key theft and insider malfeasance risk.
Polyhedra already supports 30+ chains, and Wormhole has begun integrating ZK proofs (Wormhole Native Token Transfers). But ZK bridges still carry a relatively high cost (generating a single ZK proof can cost tens of dollars), which makes them best suited for large transfers. For small and mid-size transfers, liquidity pool bridges remain more practical for now.
Q: Is it safe to withdraw from Binance to Arbitrum?
Very safe. Binance withdrawals use Arbitrum's official network, with funds routing from Binance's hot wallet through the mainnet to the Arbitrum bridge and then to the user's wallet, with the entire process relying on Ethereum mainnet security.
Q: Has the Stargate bridge ever been hacked?
Stargate's main contract has never suffered a large-scale attack. But Stargate is an application built on LayerZero, and the LayerZero protocol itself has been audited multiple times. Stargate uses a liquidity pool model, so if a pool runs dry, withdrawals could be delayed, but the contract itself can't be drained.
Q: Is the Across bridge safe?
Across is built on the UMA Optimistic Oracle, and its security depends on UMA's dispute-resolution mechanism. It has never been hacked since launch, but as an "optimistic verification" model, it's structurally a notch weaker than ZK bridges.
Q: Is Wormhole still usable today?
Wormhole underwent a major upgrade after the 2022 incident, introducing the Guardian Network and multiple rounds of audits, and has returned to normal operation. But as a "generalized bridge," it still carries structural multisig risk. Large amounts are not recommended.
Q: Is there a big difference between a 5-of-9 and a 4-of-9 multisig?
The difference is huge. Statistically, 5-of-9 is several times safer than 4-of-9. The Harmony incident used 4-of-9, so the attacker only needed 4 private keys; the Ronin incident used 5-of-9, requiring 5 private keys. Current industry consensus is that multisig thresholds should start at 8-of-12.
Q: If a bridge gets hacked, can I get my money back?
Historically, cases where users got funds back are rare. Poly Network (100% returned by the white hat), Nomad (roughly 25% recovered), and Ronin (roughly a third recovered with help from Binance and others). Most cases have a recovery rate under 10%.
Q: Can a hardware wallet protect funds sitting on a cross-chain bridge?
A hardware wallet protects your private key, not the bridge itself. If your funds are already deposited into a bridge contract, a hardware wallet can't help — if the bridge gets hacked, your share is lost just the same.
Q: How do I judge whether a cross-chain bridge is trustworthy?
Check four things: contract audit reports (at least 2 top-tier firms), multisig threshold (>= 7-of-11), operating history (>= 2 years), and peak historical TVL (over $100 million with no attack yet).
Cross-chain bridges are among the highest-risk pieces of infrastructure in DeFi. Even audited bridges can carry undiscovered vulnerabilities. For large cross-chain transfers, prioritize routing through a centralized exchange or using an official L2 bridge. This article is compiled from public case data and does not constitute investment or security advice. Please read our disclaimer.
Data sources: Chainalysis 2024 Crypto Crime Report, Rekt News, L2Beat bridge risk ratings, official incident announcements from each project (data as of April 2026).