Open to developers—and also wide open to malicious actors. Written by: 0x Compiled by: Chopper. It’s time to face the real-world issues caused by the Uniswap v4 Hook mechanism. This year, the 0x Protocol has completed 81.92 million transactions, with total volume reaching $42.67 billion—about 70% of trades calling Uniswap’s liquidity pools. Every month, we receive dozens of applications to integrate v4 Hooks, and we’ve seen both good and bad cases. But recently, a large number of malicious cases have started to emerge. Hooks can indeed enable many useful functions, including custom trading rules and liquidity management. This article is not saying these application scenarios should not exist, nor is it opposing developers building based on Hooks. Instead, an unpermissioned Hook mechanism introduces brand-new tradeoff risks for trade execution and aggregation. A typical problem is that the quoted prices returned by certain malicious pools do not match the assets users actually receive. In the past few weeks, 0x has observed a sharp increase in malicious Uniswap v4 Hooks. These malicious Hooks return one set of prices when responding to quote requests, but use a different set of prices at the time of actual settlement. While the malicious Hook implementations vary in approach, the end result is the same: by deceiving aggregators, wallets, and trading applications, they steal users’ assets. Below are the on-chain observations we found, and the countermeasures 0x has already taken. ## Problems with the Hook mechanism: Open to developers—and also open the door for wrongdoing First, the advantages. v4 Hooks bring a layer of innovation to automated market makers (AMMs). Developers can build AMMs with custom logic, and execute logic at key points in a pool’s lifecycle—such as before/after a swap, or when a liquidity provider’s position changes. Hooks can implement arbitrary logic; anyone can deploy them. Once deployed, they can directly reuse the traffic from the DeFi liquidity network with the highest integration. This is the core contradiction: while the mechanism gives legitimate developers stronger liquidity and trade-execution customization capabilities, it also makes it difficult for aggregators to determine which pools are trustworthy. Beyond lowering the development barrier, Hooks also leave enormous room for malicious activity. Malicious Hook projects don’t need to build a well-known brand, don’t need to drive users to an independent frontend, and don’t need to cold-start from scratch to obtain traffic. They only need to return extremely tempting quotes to various liquidity aggregators. The aggregator sees the best quote and routes the trade to that pool. Then, since wallets and trading applications rely on the aggregator’s output, malicious pools can exploit these infrastructure layers that users already trust to commit fraud. ## The current state of malicious Hooks Over the past 18 months, the number of Uniswap v4 Hooks has grown explosively. We conducted static and dynamic analysis on a total of 84,163 Hooks across 6 chains, and—together with real execution and settlement data—reconstructed the outcomes: only 19.4% are safe Hooks, 54.2% are malicious Hooks, and 26.4% are suspected malicious Hooks. Data statistics as of 2026‑09‑11 ## Malicious patterns vary Some are similar to rolling dice to randomly deduct fees, while others detect the EVM runtime environment to identify whether the call originates from a quote query. But the underlying behavior is highly consistent: the quoted price returned by the routing contract is not a reliable price the user can actually obtain. We observed that after trades go through malicious v4 Hooks, the assets users actually receive can shrink by up to 50% compared with the quote shown to the user at the start. ## Case 1 Hook address: 0x800cef53c3fd41109dffec62e5251bdd7acba5c7 Chain: Base Trading pair: ETH/NVDA Total executed trades: 6,516 Fee-charged trades: 3,946 (60.6%) Fee range: 0–18% Median fee rate among all executed trades: 17.96% Median fee rate among fee-charged trades: 18% Total fees collected (USD): $143,037 Data as of 2026-09-11 ## Case 2 Hook address: 0x141984423d1a28242b3dd8888c5b0daa7b13c880 Chain: BNB Chain Trading pair: USDT/WBNB Total executed trades: 4,879 Fee-charged trades: 1,619 (33.2%) Fee range: 0–12.8% Median fee rate among all executed trades: 0% Median fee rate among fee-charged trades: 12.8% Total fees collected (USD): $18,592 Data as of 2026-09-11 ## Conclusion The original intent of designing Hooks is to enhance Uniswap’s extensibility, but it has also spawned a large amount of abuse risk. Unpermissioned extensibility creates unavoidable tradeoffs on both trade execution and the trust layer. No one—routing contracts, applications, or ordinary users—can ignore this risk. This summer’s market reality has proven that permissionless liquidity is not the same as trustworthy liquidity. Just like the earlier Prop AMM chaos, this flexibility that allows developers to customize swap logic also gives malicious actors a new way to manipulate trades. Based on the observations above, we propose several key points: - Routing contracts must verify that the quotes returned by a pool match the actual execution results. - Applications need the ability to quickly filter out suspicious trade routes. - Users need to understand that a displayed best quote is only meaningful when the route behind it is safe.
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