Next.js is an open-source web framework built by Vercel that powers React-based apps with features like server-side and static rendering. Recently, a critical vulnerability (CVE) was disclosed that lets attackers bypass middleware-based authorization checks. The issue was originally discovered and analyzed by Rachid Allam (zhero). In this blog, we’ll break down the vulnerability and walk through their research and will create a Nuclei template to help you detect it across your assets.
This critical vulnerability allowed attackers to bypass authentication implemented in the middleware layer. With the popularity of this framework on the internet and within our customers' attack surfaces, our Security Research team took a deeper look at the issue.
Recently, Yasser Allam, known by the pseudonym inzo_, and I, decided to team up for some research. We discussed potential targets and chose to begin by focusing on Next.js (130K stars on github, currently downloaded + 9,4 million times per week), a framework I know quite well and with which I already have fond memories, as evidenced by my previous work. Therefore, the “we” throughout this paper will naturally refer to the two of us.
Next.js is a comprehensive javascript framework based on React, packed with numerous features — the perfect playground for diving into the intricacies of research. We set out, fueled by faith, curiosity, and resilience, to explore its lesser-known aspects, hunting for hidden treasures waiting to be found.
It didn’t take long before we uncovered a great discovery in the middleware. The impact is considerable, with all versions affected, and no preconditions for exploitability — as we’ll demonstrate shortly.
How to find Next.js on your network
Explore the critical CVE-2025-29927 vulnerability in Next.js middleware, enabling attackers to bypass authorization checks and gain unauthorized access.
