Next.js Security

A Login Page Does Not Make Your Next.js Application Secure

Your Next.js application can look polished, pass every functional test, and still expose user accounts, private tenant data, API keys, or production systems.

Next.js brings rendering, data access, mutations, and API logic into one codebase. That speed is powerful, but it creates security traps that are easy to miss: Server Actions invoked outside the intended interface, sensitive data crossing the Server Component boundary, tenant records exposed through altered IDs, sessions that cannot be revoked, and caches that return private information to the wrong user.

Next.js Security shows you how to identify these weaknesses before they become expensive incidents. Instead of memorizing disconnected rules, you will learn how to turn each threat into a clear design requirement, a reliable code pattern, and a test that proves the protection works.

With this book, you will learn how to:

• Map the true attack surface of App Router and Pages Router applications so hidden entry points do not escape review.
• Build registration, login, MFA, OAuth, passkey, recovery, cookie, and session flows that remain dependable under hostile input.
• Enforce object-level and tenant-level authorization so authenticated users cannot access records or operations that belong to someone else.
• Secure Server Components, Server Actions, Route Handlers, and API Routes at the point where protected work actually occurs.
• Prevent XSS, CSRF, injection, SSRF, unsafe redirects, path traversal, mass assignment, webhook replay, and other common web attacks.
• Protect secrets, dependencies, build artifacts, CI/CD pipelines, containers, serverless deployments, logs, and production infrastructure.
• Create security tests, audit trails, alerts, incident procedures, and pre-launch checks that help your team detect weaknesses and respond with confidence.