> For the complete documentation index, see [llms.txt](https://zokyo-auditing-tutorials.gitbook.io/zokyo-tutorials/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://zokyo-auditing-tutorials.gitbook.io/zokyo-tutorials/tutorial-61-vyper-vulnerable-versions.md).

# Tutorial 61: Vyper Vulnerable Versions

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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.