# Tutorial 61: Vyper Vulnerable Versions {% hint style="info" %} [**Book an audit with Zokyo**](https://www.zokyo.io/) {% endhint %} On July 30th, 2023, a significant vulnerability was exposed within the Vyper compiler that affected multiple Curve.Fi liquidity pools, leading to substantial financial losses. The issue stemmed from faulty reentrancy guards implemented in Vyper versions 0.2.15, 0.2.16, and 0.3.0. These vulnerabilities allowed malicious actors to bypass reentrancy protections and execute reentrancy attacks, a type of exploit that can drain contracts of funds. The flaw was eventually patched in Vyper version 0.3.1, but the incident raised critical questions about the reliability of reentrancy protections in Vyper. In this tutorial, we will deep dive into the underlying mechanics of Vyper's reentrancy vulnerability, how reentrancy attacks work, and what the developer community can learn from these exploits. This tutorial will also provide guidance on how to avoid such issues when writing smart contracts in Vyper, as well as best practices for reentrancy protection. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://zokyo-auditing-tutorials.gitbook.io/zokyo-tutorials/tutorial-61-vyper-vulnerable-versions.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.