Hey there, back again with another post! 😄

When CVE-2025–55182 dropped, it immediately became one of the most impactful Remote Code Execution (RCE) vulnerabilities in the JavaScript ecosystem. The issue affected Next.js 13+, specifically a feature called Server Actions, which quietly introduced a dangerous deserialization bug.

In this blog post, I’ll try break down CVE-2025–55182 from scratch what caused it, how to identify it in real-world applications, how to test it, and what developers need to keep the applications safe. Whether you’re a pentester, developer, or security enthusiast, this write-up will make you fully understand how this vulnerability works and how to detect it.

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Understanding Next.js

Next.js is a framework built on React. In newer versions (13+), Next.js introduced Server Actions.

What is Server Actions?

They allow you to write a server-side function directly inside your React component:

async function addUser(data) {
  // runs on the server
}

Instead of building an API endpoint, the browser automatically sends a special POST request that triggers these functions. These requests are not normal JSON APIs. They use something called the React Server Components protocol (RSC/Flight).
This “special” request structure is…