Web3 Frontend Attacks: Hacker's New Playground

The Invisible Layer We Forgot to Protect

When most people talk about Web3 security, they usually think of smart contracts. This makes sense. After all, these pieces of code govern real assets, define protocol logic, and protect billions of dollars in user funds. For years, security teams have devoted endless effort to discovering reentrancy vulnerabilities, access control issues, arithmetic errors, and subtle bugs that only appear under specific execution paths. But amidst all this obsession with what happens on-chain, we have overlooked the first thing that the vast majority of users actually interact with: the front end.

The front end has always been seen as a shiny shell, an interface that helps users interact with the blockchain. However, this "shell" is rapidly becoming one of the most abused layers in the entire ecosystem. While smart contracts are immutable and auditable, the front end is mutable, centralized, and served by infrastructure that is completely outside the guarantees of the blockchain. Yet, it is these that construct the transaction payloads requiring users to sign. If this hasn't scared you yet, it should.

The Trust Interface Means Trusting the Attacker

The real danger of the front end is not necessarily the technical complexity; rather, it is the misplaced trust. Most users do not know what they are actually signing when confirming a transaction. They rely entirely on what the front end shows them.

A "Swap" button may be triggering an approval. A staking interface may be passing a delegation call. Unless the wallet decodes the data in a human-readable format, which many wallets still do not do, users cannot verify what they are doing.

This makes front-end intrusion one of the most effective ways to steal funds in Web3. Attackers do not need to compromise contracts or find vulnerabilities in the core protocol. All they need is a way to manipulate the front end, even if only temporarily, allowing them to invisibly sit between the user and the blockchain. Every click becomes an opportunity for hijacking intent.

How These Attacks Occur

The implementation methods of these attacks are nothing special. Sometimes it is as simple as DNS hijacking, where the attacker can access the project's domain records and point them to malicious servers. In other cases, the attacker injects code through infected dependencies, replacing malicious logic and modifying transaction data before passing it to the wallet. In some cases, the front end is directly compromised by accessing the cloud dashboard or CDN configuration, allowing the attacker to change the UI scripts in real time.

The outcome is always the same. Users access the application as usual, connect their wallets, and sign transactions they believe to be safe. But what they are signing is completely different, often approving an untrusted contract or transferring tokens to a wallet controlled by an attacker. And since the blockchain executes exactly as signed, there is no undo button.

Recent events proving this point

We have seen some painful examples in this regard. One of the most famous examples is the Curve Finance incident in 2022, where the attacker took control of Curve's DNS and provided users with a fake front end. The website looked exactly the same. The wallet prompts also appeared normal. But behind the scenes, every transaction was routed to the attacker's wallet. Nearly $600,000 was lost in just a few hours.

Another example is BadgerDAO, which lost over $100 million after an attacker injected malicious JavaScript into its frontend. The code quietly altered the transaction payloads of specific users (especially whales), leading these users to click into their own demise.

The commonality of these events is that the smart contracts remain unchanged. The logic is sound, the audits are clean, but when the front end tells a different story, all of this becomes irrelevant.

Why This Problem Won't Disappear

The reason why frontend security is particularly difficult in Web3 is that it belongs to a strange gray area. It is off-chain, so most on-chain security tools cannot monitor it. It is often overlooked during audits, especially in projects that prioritize delivery over security. Moreover, it heavily relies on centralized infrastructure, such as DNS, cloud storage, and JavaScript package registries, none of which provide the same guarantees as blockchain.

Worse still, the tools surrounding front-end validation are still immature. Unlike contract bytecode that can be verified on-chain, front-end code frequently changes, is rarely fixed or hashed, and is almost never published in a way that users can inspect. This creates a perfect environment for targeted attacks, especially during sensitive periods such as token launches, airdrops, or UI upgrades.

What needs to change

To ensure the safe development of Web3, security must extend beyond smart contracts. Developers must treat the front end with the same paranoia and rigor as the back end. This means locking down dependencies, avoiding unnecessary third-party scripts, protecting DNS configurations, and considering front-end audits as part of every major release.

Wallet providers should also play a role. Users need to have a clearer understanding of what they are signing. This may mean improved decoding, better warnings, and even front-end authenticity checks. Currently, there is an over-reliance on the interface, while efforts to verify its integrity are lacking.

From the user's perspective, the advice is stern but honest: do not blindly trust any UI. If you are interacting with high-value protocols, do not just check the domain name. Check the source code. Use browser extensions that track malicious contracts. If something feels off, do not sign.

Conclusion

Web3 is not just about trustless execution. It is about the entire trust boundary, its starting point, how it transfers, and its endpoint. Now, the front end just happens to be in the middle of that boundary and has become a playground for anyone clever enough to exploit the gap between what users see and what is signed.

Your contract may be perfect, but if your frontend is attacked, the result is the same. Funds lost, trust broken, and users want to know how everything went wrong. It's time for the industry to stop treating the frontend as an afterthought. Because for hackers, it has become the primary target of their attacks.