Blockchain bridges and cross-chain security issues

introduction

Blockchain interoperability is a core feature of the technology, which is currently widely used in DeFi apps. Investors are attracted to the option of profiting from many chains simultaneously. Users on the Bitcoin blockchain can earn revenue on the Ethereum chain, and users on the Ethereum chain have the option to move their assets or wrapped versions of assets to other networks so that one blockchain remains connected to the other. However, this interoperability and flexibility comes with tradeoffs. These create problems that don’t exist if the assets stay on one chain.

What is a blockchain bridge?

A blockchain bridge is a tool that allows users to move data, messages, and assets from one network to another. You should know that blockchain is a tight ecosystem and cannot communicate with the outside world or with another blockchain. They rely on oracles for external information and bridges to connect with other chains. These bridges act as intermediaries, locking digital currencies onto one chain and making them available on other chains in a wrapped version or other equivalent format. This hand option allows users to take advantage of applications, liquidity, and revenue opportunities not available on the native chain.

Main security issues

Whenever you take money out of your physical or virtual wallet, there is a chance that it could be stolen, intercepted, or fraudulently induced to mistakenly transfer your money to someone else’s account. The same thing can happen in the DeFi world when moving digital assets from one chain to another. According to recent industry analysis, cross-chain bridges have been exploited to steal assets totaling approximately $2.8 billion as of mid-2025. This diagram shows that bridges remain a prime target for attackers. There are many possible causes for such large-scale exploitation.

1. Risks of weak on-chain verification

There are many types and types of blockchain bridges. Some of them use a basic level of security, while others use smart contract-driven security. The former type of tools rely heavily on a centralized backend to perform basic operations such as minting, writing, and token transfers, while all validation is performed off-chain.

Bridges that use smart contracts for security have some advantages over other types of bridges. The smart contract validates the message and performs the validation on the chain. When a user brings funds into the blockchain network, the smart contract generates a signed message as proof. This signature is used to verify withdrawals on another chain. This is where the security flaw arises. If this on-chain validation fails, an attacker could steal funds passing through the bridge. They quickly bypass verification or forge the required signatures.

Additionally, when blockchain bridges apply the concept of wrapped tokens, an attacker can route those tokens to their own accounts and seize the assets of the sender and receiver. For example, a user plans to send $ETH coins from the Ethereum chain to the Solana chain. Currently, the bridge receives $ETH from the Ethereum chain and issues $ETH wrapped on the Solana chain. The problem gets even worse when bridges require endless approvals to save on gas bills.

Two dangerous things are happening right now. First, if an attacker successfully intercepts a transaction, the user’s wallet will be exhausted due to infinite authorizations. Second, infinite authorizations remain valid long after the transaction is executed. Therefore, even if the initial transaction was secure, the user could leave the chain, but an attacker could still exploit this vulnerability.

2. Issues with off-chain verification

Blockchain bridges may use off-chain verification systems in addition to on-chain verification, which is even more dangerous. Before we get into the details of risks, we need to understand how off-chain validation systems work. On-chain validation systems run on the blockchain itself, with bridges checking transaction signatures or using their own smart contracts to validate transactions. When a bridge uses off-chain validation, the bridge relies on servers external to the blockchain. The server checks the transaction details and sends a positive report to the target chain.

For example, let’s say a user deposits a token on the Solana chain and wants to use it on Ethereum. The bridge server validates the initial transaction and signs the instructions on the Ethereum chain. This is the same as being able to complete the procedure just by looking at the receipt, and there is a possibility that it is a forgery. This vulnerability is primarily due to excessive privileges being placed in the hands of the bridge server. If the attacker is able to deceive, the system is compromised.

3. Risk of mishandling of native tokens in blockchain bridges

The bridge sends native tokens directly to the destination blockchain network, but requires prior permission to send other tokens. It includes various systems to perform these tasks. Problems arise when the bridge mistakenly fails to manage the distinction. If users transfer $ETH tokens using a system for non-native utility tokens, they will lose their funds.

Additional risks arise if the bridge allows users to enter arbitrary token addresses. If the bridge does not strictly limit the tokens it accepts, attackers can exploit this freedom. Many bridges use whitelists to only allow approved tokens, but native tokens do not have addresses and are often represented by a zero address. If this case is poorly handled, an attacker may be able to bypass the check. This triggers a transaction without actually transferring the tokens, effectively tricking the bridge into releasing assets it did not receive.

4. How configuration errors break blockchain bridges

Blockchain bridges rely on special administrator settings to control important actions. These settings include authorizing tokens, managing signers, and configuring validation rules. If these settings are incorrect, the bridge may malfunction. In a real case, a small change during the upgrade caused the system to accept all messages as valid. This allowed the attacker to send fake messages and bypass all checks, leading to significant losses.

conclusion

In short, while blockchain bridges offer great utility in allowing you to make money on many chain networks simultaneously, they also pose serious risks that you need to learn how to manage when using these tools. Blockchain bridges play a critical role in enabling cross-chain interoperability and expanding DeFi opportunities, but they remain one of the weakest parts of the ecosystem. Weak on-chain validation, risky off-chain validation, mishandling of native tokens, and simple configuration errors make bridges prime targets for large-scale exploits.

As cross-chain activity continues to grow, users and developers must prioritize security, limit authorization, prioritize well-audited designs, and understand the risks involved. Ultimately, more secure bridge architectures and informed usage are essential to ensure that interoperability does not come at the cost of asset loss.