The explosion of the blockchain ecosystem over the past decade has created a multi-chain reality, where networks operate as isolated oases with distinct rules, consensus mechanisms, and programming languages. To address this fragmentation, cross-chain protocols and bridges have become essential infrastructure, allowing the free flow of capital and data. However, this very convenience has opened up one of the most dangerous and costly attack fronts in the history of decentralized finance (DeFi).
According to experts at Tan Phat Digital, cross-chain interactive smart contracts are extremely dangerous because they create huge centralized liquidity weaknesses, possess complex logic structures that go beyond normal control capabilities, and often face risks from centralized governance. Statistics show that bridge attacks have accounted for 69% of all funds stolen in the DeFi space over the past two years, with total losses reaching billions of dollars. This report will delve into the analysis of root causes, attack mechanisms, and technical loopholes in validating transactions between different virtual machines.
Risk classification and root cause families
Securing cross-chain smart contracts is not just a matter of simple source code but also a synthesis of program structure elements and environmental assumptions. These contracts concentrate high asset values and complex logic in small, immutable programs, where even the smallest error can lead to catastrophic losses. Unlike conventional decentralized applications (DApps), the functionality of cross-chain bridges depends on the coordination of information both on-chain and off-chain, which significantly expands the attack surface.
Risk taxonomy studies have identified eight "families" of root causes of vulnerabilities:
Control flow and external calls:Risk of interacting with contracts unknown coin.
State integrity and arithmetic safety: Numerical overflow or errors in balance updates.
Environment dependency and access control: Variables from the blockchain or abused admin authority.
Input validation and cross-domain protocol assumptions: False belief in data from another chain that there is no full root verification mechanism.
In a cross-chain context, cross-domain protocol assumptions are the most dangerous. The immutability and composability of smart contracts amplify the impact of flaws: a single vulnerability can be replicated across thousands of instances, exploited without permission, and spread through interactions between contracts.
See also: What is a Cross-chain Bridge?
Liquidity Concentration Weakness: A "Honeypot" for Malicious Actors
One of the core reasons why bridges have become a prime target for hackers is their centralized design liquidity center. As observed by Tan Phat Digital, a common design of an inter-chain bridge is to lock a large amount of tokens in just one or two smart contracts on the source chain, creating an extremely high reward if the attack is successful. These "sinks" of liquidity accumulate hundreds of millions, sometimes billions, of USD, making them the highest-value targets in the entire crypto ecosystem.
This risk is exacerbated by the lack of end-to-end value accounting mechanisms. When an asset is locked on chain A and a representative version (wrapped token) is minted on chain B, the security of the asset on chain B depends entirely on the integrity of the contract locked on chain A. If the contract on chain A is hacked, all tokens on chain B will become "empty shells" without collateral, causing a chain collapse in that chain's ecosystem.
Technical analysis of bridge attack mechanisms connect
Bridge attacks are typically divided into two main categories: code attacks that exploit vulnerabilities in smart contracts, and network design attacks that typically through social engineering or validator hijacking.
Custodian Attacks
Custody attacks target smart contracts where assets are locked. Below is a detailed analysis of typical events:
Binance Bridge (October 2022):
Mechanism: Manipulation of IAVL Merkle evidence to illegally mint tokens.
Damage: About 568 million USD.
Cause: Logical error in parsing and validating using evidence.
Qubit Finance (January 2022):
Mechanism: Exploited logic error in sending malicious data to mint tokens without deposit.
Loss: Approximately 80 million USD.
Cause: Input validation error in valid source code copper.
Wormhole (February 2022):
Mechanism: Bypass signature check by using fake system account on Solana.
Loss: Approximately 326 million USD.
Cause: Failure to authenticate sysvar system program (fake system account impersonation).
In the Wormhole incident, the attacker took advantage of a vulnerability in the verify_signatures function. Instead of using Solana's real system program to verify the signature, the attacker injected a fake account. Because the contract did not check the validity of the sysvar account, it accepted the forged signatures as correct, resulting in the unauthorized minting of 120,000 wETH.
Message Exploits and Forgery (Message Exploits)
Message Exploits are a more sophisticated type of attack that targets the cross-chain communication layer. These attacks focus on intercepting, manipulating or falsifying transmitted data.
The Nomad Bridge incident (August 2022) is a classic example of mistakes in message structure. A contract update initialized the value of "trusted root" to 0x00. In Nomad's system, this value coincidentally coincided with the status of an unproven message. As a result, every incoming message is automatically considered valid. This creates an unprecedented "decentralized looting" where even people without technical knowledge can copy other people's transaction data to illegally withdraw funds.
Most recently, in February 2026, the CrossCurve protocol was also attacked through spoofed messages. An attacker exploited a gateway verification bypass vulnerability in the ReceiverAxelar contract, allowing anyone to call the expressExecute function with a crafted message to trigger illegal token unlocking.
See also: What is bridge hacking?
Risks from centralized governance and private key management
Although Web3 worships decentralization, in fact many leading inter-chain bridges are still operating under a governance model highly centralized or use small-scale validators. This is a fatal operational weakness.
Disaster from private key compromise
Private keys manage bridge operations, approving transactions based on digital signatures or a certain threshold of signatures (quorum). When these keys are compromised, the attacker can control the entire treasury:
Ronin Bridge (March 2022): Hackers have infiltrated and controlled 5 out of 9 authentication nodes, allowing 624 million USD to be withdrawn in a single transaction.
Harmony Horizon Bridge (June 2022): Hackers took control 2 of 5 signing nodes through server compromise, stealing 100 million USD.
Multichain (July 2023): All private keys are under the control of a single individual, causing the system to be paralyzed when that individual encounters legal problems.
Probability of failure over time
Mathematical analysis from Tan Phat Digital on the probability of validator hacks shows that trust-based bridges will almost certainly be hacked in the long term. If an individual validator has an annual compromise rate of 2-5%, the 3-year failure probability of validation thresholds is as follows:
5 out of 9 threshold (Ronin style): Up to 89.3% failure probability.
7 out of 15 threshold: Failure probability approximately 76.2%.
Threshold 11 out of 21:Probability of failure is about 63.8%.
The conclusion from this data is clear: no matter how many validators you add, if the architecture is still based on trust in humans and individual servers, the probability of being compromised will approach 100% over time.
The gap between virtual machines (VMs) and authentication asynchrony
The interaction between EVM-compatible chains (like Ethereum, BSC) and non-EVM chains (like Solana, Aptos, Bitcoin) creates major technical challenges due to differences in storage architecture and consensus mechanisms.
Language and memory safety differences
EVM chains use Solidity, while Chains like Aptos use Move or Solana uses Rust. The risk occurs when developers bring EVM thinking to Non-EVM chains. For example, in EVM, invoking another contract is a simple action, but in Solana, a lack of account ownership control can lead to a security disaster.
Finality and Reorganization Risk
Differences in finality rules between chains can be exploited by hackers. Tan Phat Digital emphasizes two main types:
Probabilistic Finality: Like old Bitcoin or Ethereum, a certain number of blocks is needed to ensure safety.
Deterministic Finality: Like Cosmos or Algorand, there is finality immediately after the block is confirmed.
If a bridge connecting escrow too quickly before finality is reached, and then the source chain restructures (Chain Reorg), the attacker can perform a cross-chain "double spend" attack.
Additional risks and network layer attack vectors
Besides contract logic errors, bridges also face threats from the network infrastructure:
BGP Hijacking (BGP Hijacking): Hackers impersonate the IP address of the bridge service provider to redirect traffic and forge transaction confirmations.
Supply Chain Attacks: Infiltrate social network accounts or personal devices of the administration team to appropriate private keys.
Towards secure interoperability solutions more
The industry is shifting dramatically toward trust-minimized models. Typical solutions include:
On-chain Light Client: Runs a scaled-down version of another blockchain right inside the smart contract, allowing direct verification of block headers without the need for an intermediary.
ZK-SNARK/STARK: Compresses the verification process of thousands of validator signatures into a small proof, reducing gas costs from millions to a few hundreds thousands.
1-of-N Trust Model: Only one honest entity is needed for the system to function correctly, eliminating the risk of majority collusion (51% attack).
Projects like Succinct Labs, Polyhedra, and Chainlink CCIP are leading this trend by using independent risk management networks and Zero-Knowledge technology to replace trust in humans with belief in mathematics.
Frequently Asked Questions (FAQ)
1. What is a cross-chain bridge? It is a protocol that allows the transfer of assets, data or smart contracts between independent blockchain networks. It helps solve the blockchain's isolation problem, allowing users to transfer tokens from one network to another to take advantage of lower gas fees or specific DeFi applications.
2. Why are bridge attacks so damaging?Because bridges often act as centralized liquidity "sinks" (Honeypots), locking up billions of dollars in assets as collateral to mint representative tokens on other chains. A single logic error could help hackers drain all of this money in minutes.
3. How does the Lock-and-Mint model work? This is the most common model, where the original asset is locked in a smart contract on the source chain, then a "wrapped" version (representative token) of equal value is minted on the destination chain. When users want to return to the original chain, they burn wrapped tokens to unlock the original assets.
4. How is a "Message Exploit" different from a regular source code attack? Source code attacks often exploit logical errors in the contract itself (for example, number overflow errors), while message errors focus on manipulating, intercepting or falsifying data transmitted between chains. Hackers can send fake messages that make the target contract believe that a deposit has been made on the source chain.
5. Why is the 2022 Nomad Bridge incident called a "decentralized heist"? Because a buggy update set the "trusted root" value to 0x00, causing the system to automatically treat every incoming message as valid. This allows anyone, even non-technical people, to simply copy someone else's transactions and change their wallet address to withdraw funds.
6. How does "Finality Risk" affect bridges?If a bridge records a deposit too quickly on the source chain before it reaches an irreversible state (finalized), and then the source chain is reorged, the original transaction disappears but the tokens that were minted on the destination chain still exist, creating "unbacked" tokens.
7. What is the 1-of-N security model? This is an extremely strong security model used in ZK-Bridges and Light Clients. It only requires a single honest entity (prover) operating in the entire system to ensure integrity, instead of relying on a 51% majority like traditional models.
8. How does Chainlink CCIP help mitigate security risks? CCIP uses a "defense in depth" architecture that includes an independent Risk Management Network, which continuously monitors and reserves the right to suspend cross-chain operations if abnormalities are detected or withdrawal limits are exceeded.
9. How does BGP Hijacking attack the bridge? This is an attack on the Internet infrastructure layer instead of the source code. Hackers impersonate the IP address ranges of validator nodes or Oracles to redirect data to their servers, thereby falsifying transaction confirmations to steal funds.
10. Why are ZK-Bridges considered the future of cross-chain? Because they replace trust in humans (validator team) with trust in mathematics (zero-knowledge proof - ZKP). ZK-Bridges allows for direct and cheaper verification of another chain's state through compressed proofs, eliminating the risk of validator collusion.
11. What risks does wrapped tokens pose to users? The value of wrapped tokens depends entirely on the collateral locked on the bridge. If the bridge is hacked and the original assets are taken, the wrapped token will become worthless and lose its 1:1 parity (depeg).
12. What lesson does the Ronin Bridge (2022) incident teach us about governance? This incident shows the risk of concentrating power in too few authentication nodes (only 9 nodes, hackers need 5 to control). In addition, maintaining temporary access rights but not revoking them (as in the case of Axie DAO allowing Sky Mavis to sign transactions on its behalf) created a fatal vulnerability.
13. Is it possible to completely prevent message tampering (spoofing)?Possibly by implementing strict gateway verification mechanisms and requiring cryptographic proofs of the source chain state instead of just trusting the signatures of off-chain relayers.
14. Why are some Non-EVM chains more secure against cross-chain errors? Languages like Move (in Aptos/Sui) are designed with resource safety in mind, helping to prevent some common errors like reentrancy or overflow logic errors that Solidity on EVM often suffers from.
15. What should users check before using a bridge?It is necessary to check whether the bridge has been audited by multiple entities, whether there is a bug bounty program, whether the governance model is centralized (multisig) or decentralized (ZK/Light Client), and how long the finality confirmation wait time is to avoid the risk of reorg.
Inter-chain interaction through smart contracts is a "double-edged sword". While it opens up endless liquidity, it also creates enormous systemic risks. Tan Phat Digital recommends that users and organizations apply an "assume breach" mindset, deploy multi-layered protection layers, and always prioritize using bridges with mathematical architecture (ZK-Bridges) instead of centralized validator-based systems to ensure asset safety in the multi-chain era.
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