The Decentralized finance (DeFi) ecosystem recently faced a major stress test after a critical vulnerability was discovered in versions of the Vyper programming language. The exploit resulted in the theft of millions of dollars worth of cryptocurrencies on July 30. Pools using Vyper 0.2.15, 0.2.16, and 0.3.0 were targeted, with at least four liquidity pools on the Curve Finance protocol falling victim to the malfunctioning reentrancy lock. This article delves into the implications of the vulnerability, its impact on DeFi projects, and the potential risks faced by the wider ecosystem.

Vyper – A Contract-Oriented Programming Language for DeFi

Vyper is a specialized contract-oriented programming language designed specifically for the Ethereum Virtual Machine (EVM) within the decentralized finance (DeFi) ecosystem. As a Pythonic language, Vyper shares similarities with the widely-used Python programming language, making it an accessible choice for developers familiar with Python who are venturing into the Web3 space.

Vyper Programming Language

Vyper was created to address security concerns and enhance smart contract development, emphasizing simplicity and clarity in its syntax. Its focus on readability and avoidance of complex features reduces the risk of errors and potential vulnerabilities, ensuring a safer environment for DeFi protocols. Due to its user-friendly nature and efficient execution on the EVM, Vyper has gained popularity as a reliable language for creating secure and auditable smart contracts in the rapidly expanding world of DeFi.

Vulnerability and Targeted Pools

The Reentrancy attack on Curve Finance via Vyper’s exploit

The vulnerability in Vyper’s programming language posed a significant risk to DeFi protocols utilizing the affected versions. At least four liquidity pools on the Curve Finance protocol were targeted, leading to considerable outflows. The exploited pools include aETH/ETH, msETH/ETH, pETH/ETH, and CRV/ETH. Curve Finance assured its users that all remaining pools were safe and unaffected by the bug. The issue of reentrancy lock malfunction could potentially expose all pools with wrapped Ether (WETH) to similar attacks, raising concerns among the DeFi community.

Impact on DeFi Projects

The attack had far-reaching consequences on several DeFi projects, with Alchemix’s alETH-ETH experiencing outflows of $13.6 million, PEGd’s pETH-ETH pool drained by $11.4 million, and Metronome’s sETH-ETH pool hacked by $1.6 million. Furthermore, over 32 million Curve DAO (CRV) tokens, worth more than $22 million, were drained. Decentralized exchange Ellipsis also reported that a limited number of stable pools with BNB were exploited using an old Vyper compiler. These incidents triggered a negative impact on CRV’s price, causing a decline of over 12% at the time of writing.


The Vyper vulnerability has highlighted the importance of robust security measures in the DeFi ecosystem. The exploitation of multiple liquidity pools underscores the need for thorough stress testing and continuous auditing to safeguard user funds. As the DeFi space continues to evolve, developers and protocols must remain vigilant against potential vulnerabilities and collaborate on implementing best practices. The incident serves as a stark reminder of the risks associated with smart contract programming languages and the necessity for timely updates and security patches to protect the integrity of DeFi protocols.

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