Design Flaw in Uniswap v4 Hook? 0x Reveals Over Half of Hooks Exhibit Malicious Behavior

Open to developers, but also a gateway for wrongdoers.

Written by: 0x

Compiled by: Chopper, Foresight News

It’s time to confront the real issues with the Uniswap v4 Hook mechanism.

This year, the 0x protocol has completed 81.92 million transactions, with a total trading volume of $42.67 billion, and about 70% of transactions call on Uniswap’s liquidity pools.

We receive dozens of audits and applications to access v4 Hook every month, witnessing both good and bad cases. However, recently, a surge of malicious cases has emerged.

Hooks can indeed enable many practical functions, including custom trading rules and liquidity management. This article does not argue against the existence of these application scenarios or oppose developers building on Hooks; however, the permissionless Hook mechanism introduces new risk trade-offs for transaction execution and aggregation. A typical issue is that some malicious pools return quotes that do not match the actual assets users receive.

In the past few weeks, 0x has observed a sharp increase in the number of malicious Uniswap v4 Hooks. These malicious Hooks return one price during the quote request but use another price during actual settlement. The implementation patterns of malicious Hooks vary, but the end result is the same: they deceive aggregators, wallets, and trading applications to steal user assets.

Here are the phenomena we have observed on-chain, along with the measures 0x has taken in response.

Issues with the Hook Mechanism: Open to Developers, but Also a Gateway for Wrongdoers

Let’s start with the advantages. v4 Hook brings a layer of innovative capability to automated market makers (AMM). Developers can build AMMs with custom logic, executing logic at critical points in the pool's lifecycle, such as before and after swaps, or when liquidity provider positions change. Hooks can implement any logic, and anyone can deploy them; once deployed, they can directly reuse traffic from the most connected liquidity networks in the DeFi ecosystem.

This is the core contradiction: while this mechanism provides legitimate developers with stronger liquidity and transaction execution customization capabilities, it also makes it difficult for aggregators to discern which pools are trustworthy.

In addition to lowering the development threshold for developers, Hooks also leave significant operational space for malicious behavior. Malicious Hook projects do not need to build a well-known brand, guide users to access independent front-ends, or acquire traffic from scratch. They only need to return highly attractive quotes to various liquidity aggregators.

When aggregators see the optimal quotes, they will route transactions to that pool. Wallets and trading applications rely on the results output by aggregators, allowing malicious pools to exploit this trusted infrastructure to commit wrongdoing.

Current State of Malicious Hooks

In the past 18 months, the number of Uniswap v4 Hooks has exploded. We conducted static and dynamic analyses on a total of 84,163 Hooks across 6 chains and reviewed actual transaction data: only 19.4% are safe Hooks, 54.2% are malicious Hooks, and 26.4% are suspected malicious Hooks.

Data statistics as of September 11, 2026

The malicious behavior patterns vary: some resemble random fees like dice rolls, while others detect the EVM runtime environment to identify whether it comes from a quote inquiry. However, the underlying behavior is highly consistent; the quotes returned by the routing are not reliable prices that users can actually obtain. We have observed that transactions through malicious v4 Hooks result in users receiving assets that can be up to 50% less than the quotes initially presented to them.

Case 1

Hook Address: 0x800cef53c3fd41109dffec62e5251bdd7acba5c7

Chain: Base

Trading Pair: ETH/NVDAc

Total Transactions: 6,516

Fee Transactions: 3,946 (60.6%)

Fee Range: 0-18%

Median Fee for All Transactions: 17.96%

Median Fee for Transactions with Fees: 18%

Total Fees Collected (USD): $143,037

Data as of September 11, 2026

Case 2

Hook Address: 0x141984423d1a28242b3dd8888c5b0daa7b13c880

Chain: BNB Chain

Trading Pair: USDT/WBNB

Total Transactions: 4,879

Fee Transactions: 1,619 (33.2%)

Fee Range: 0-12.8%

Median Fee for All Transactions: 0%

Median Fee for Transactions with Fees: 12.8%

Total Fees Collected (USD): $18,592

Data as of September 11, 2026

Conclusion

The original intention of designing Hooks was to enhance Uniswap's scalability, but it has also given rise to significant abuse risks. Permissionless scalability introduces trade-offs in transaction execution and trust that cannot be ignored by routing contracts, applications, or ordinary users.

The current market situation this summer proves that permissionless liquidity does not equate to trustworthy liquidity. Just like the previous chaos with Prop AMM, this flexibility that allows developers to customize swap logic also provides wrongdoers with new means to manipulate transactions.

Based on the above observations, we propose several insights:

• Routing contracts must verify that the quotes returned by pools align with the actual execution results;
• Various applications need to have the capability to quickly eliminate suspicious transaction routes;
• Users need to understand that a displayed optimal quote is only meaningful if the route behind it is secure.

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