How to Secure File Uploads in Next.js

File uploads are one of those features that look simple until you think about the security side. A user uploads a file, your route accepts it, and everything seems fine. But what if that file is not what it claims to be? A renamed executable can look like a harmless PDF. A ZIP archive can hide traversal tricks or resource-exhaustion problems. A document can carry risky structures you would never catch by checking only the filename extension. That is why upload endpoints are part of your attack surface. In this article, I will show you how to secure file uploads in a Next.js App Router application by scanning them before storage with pompelmi , an open-source upload security tool for Node.js. We will build a minimal example that: accepts a file from a browser form scans it on the server returns a verdict blocks suspicious or malicious uploads before they reach storage Why file upload validation is usually too weak A lot of upload handlers still rely on checks like these: file.name.endsW