Security Guidelines in Next.js

Anton Ioffe - October 29th 2023 - 8 minutes read

As a senior developer, you're well aware of the evolving threats and challenges in maintaining web application security. In the modern web development landscape, Next.js has emerged as a go-to tool owing to its efficiency and versatility, but like all technologies, it also demands certain precautions. This article delves into advanced security measures you can take while working on Next.js applications—from implementing HTTP security headers to protecting API routes, from CSRF protection to error handling, and not forgetting the importance of data sanitization and the effective use of middleware. Dive in to understand these critical elements better and learn how to successfully bolster your application's security, piece by piece.

Implementing HTTP Security Headers in Next.js

HTTP security headers are an essential part of making your Next.js application safer and more robust against common web threats including cross-site scripting (XSS) and clickjacking. When correctly implemented, these security headers control and guide the behaviour of the browser, limiting potential attack vectors.

Let's take a closer look at some of the key HTTP security headers that you should consider incorporating:


This header prevents the browser from trying to MIME-sniff the content type and forces it to stick with the declared content-type. This defense is especially important for avoiding scenarios where scripts get executed due to MIME type manipulation.

Strict-Transport-Security (HSTS)

The HSTS header ensures that the browser only connects to your application using a secure HTTPS connection. Even if your application redirects users from HTTP to HTTPS, an attacker might still intercept this, eavesdrop, or change sensitive information. Implementing HSTS makes the browser bypass any insecure HTTP connection, forcing it to use secure HTTPS connections only.

Content-Security-Policy (CSP)

The CSP header improves your app's security by limiting the sources of executable scripts or stylesheets. It helps prevent attacks like cross-site scripting and other code-injection attacks. You can customize the policy to allow scripts to be loaded from certain domains only.

const securityHeaders = {
  "Content-Security-Policy": "default-src 'self'; script-src;",
  "Strict-Transport-Security": "max-age=31536000; includeSubDomains",

To add these security headers to your Next.js application, include them in your next.config.js file. This practice ensures that every server response includes the declared security headers.

// next.config.js

module.exports = {
  async headers() {
    return [
        // Apply these headers to all routes
        source: '/(.*)',
        headers: securityHeaders,

Remember that one size does not fit all when implementing security headers. Your policy should fit the needs of your app and its functionality. A strict policy might break your app if not appropriately configured. Always test comprehensively when setting up new security measures. A safer app means a better user experience and less worry about vulnerabilities.

Protecting API Routes and Data Handlers

Securing API routes in Next.js usually revolves around implementing reliable authentication strategies. This often leverages JSON Web Tokens (JWT) or external libraries like NextAuth.js. JWT comes in handy when managing user sessions securely since it includes encoding the data to safeguard it. Whereas, NextAuth.js is a robust tool that provides an easy-to-setup authentication solution with various providers like Google, Facebook, and Twitter. However, it's not a silver bullet. Take into account the complexity of your application, the level of user interaction, and the specific data you're looking to protect when deciding your authentication strategy.

import { getSession } from 'next-auth/react';

export default async function handler(req, res) {
    const session = await getSession({ req });
    if (!session) {
        res.status(401).json({ error: 'Unauthorized' });
    // Handle the protected logic here 
    // ... 
    res.status(200).json({ success: true });

Aside from securing API routes, it's also essential to consider how you handle data in your Next.js app, mainly because of data handlers' diversity. There are several models including; HTTP APIs recommended for large existing projects, the Data Access Layer recommended for new projects, and Component Level Data Access. Each model has its potential vulnerabilities, but they can all be made secure with careful consideration and implementation.

In case of Component Level Data Access, each component has its direct data access point. This ensures that only the data needed by that component is fetched, which reduces the attack surface area but also requires more granular security checks. On the other hand, using the Data Access Layer method, you can centralize data access security, which simplifies checks and validation but may expose more data points to malicious actors.

import { cache } from 'react'; 

// Cached helper methods makes it easy to get the same value in many places

Choosing the right data handling model according to the nature and scale of your app is crucial to ensure a robust security posture. The choice between HTTP APIs, Data Access Layer, or Component Level Data Access should consider factors like the complexity of the app, the amount of data being handled, and the level of authorization required. Proper implementation of these concepts can create a secure, maintainable, and high-performing Next.js application.

Overall, maintaining security in API routes and data handlers is about understanding the unique architectural landscape of your Next.js app, and thoughtfully implementing security measures. With the shifting nature of security threats, consistently updating and reevaluating these measures remains a necessity for all Next.js developers.

Implementing CSRF Protection and Rate Limiting

Cross-Site Request Forgery (CSRF) attacks can lead to serious security breaches, such as account takeover, data theft, and malware installation. One effective way to protect against CSRF attacks is to implement CSRF tokens. These security tokens ensure that every request made from a client is verified and trusted. Consider using axios for making HTTP requests from the client to the server. axios helps with creating and managing CSRF tokens in cookies by automatically including the CSRF token in every request header.

// pages/api/csrf-token.js
import { createCSRFToken } from '../../utils/csrf';

export default function handler(req, res) {
    const csrfToken = createCSRFToken();
    res.status(200).json({ csrfToken });

Then, inside a form component, import and use this token:

// The useCSRF hook

import { useState, useEffect } from 'react';
import { getCSRFToken } from '../api/csrf-token';

function MyForm() {
    const [csrfToken, setCsrfToken] = useState('');

    useEffect(() => {
        async function fetchCSRFToken() {
            const response = await getCSRFToken();

    }, []);

    // Use csrfToken in your form
    // ...

Implementing rate limiting on your API routes is also a crucial security step. Rate limiting prevents brute-force and Denial of Service (DoS) attacks by limiting the number of requests a client can make within a specified time window. Packages such as express-rate-limit are useful for this purpose.

// Rate limiting with express-rate-limit

import rateLimit from 'express-rate-limit';

const limiter = rateLimit({
    windowMs: 15 * 60 * 1000, // 15 minutes
    max: 100, // limit each IP to 100 requests per windowMs
    message: 'Too many requests, please try again later.'


Providing a balance between application usability and security can often be challenging. Overly strict rate limits may affect the user experience, while too lax restrictions may not provide adequate protection. Therefore, careful, conflict-free configuration of rate limits is key to enhancing the security and performance of your application.

In conclusion, implementing CSRF protection and rate limiting are vital security measures to enhance your Next.js applications. Understanding the risks and effectively using tools at your disposal will not only improve your application's security but also your skills as a developer. These methods will go a long way in protecting your application against CSRF and brute-force attacks.

Error Handling and Data Sanitization

In web application development, error handling is a critical tool for safeguarding your application from potential security vulnerabilities. When dealing with server-side errors in Next.js, it's vital to prevent your application's sensitive information often contained in error messages and stack traces from being exposed. Consider that when server-side errors are rethrown on the client side, they must be managed effectively in the user interface (UI) to prevent sensitive data exposure.

React's production mode provides a means to secure error information. Instead of emitting the actual error message, it emits a hash representing the error. The hashed error can then be associated with its instances and linked to server logs, limiting the exposure of sensitive data.

But, error handling isn't the only aspect of security. Cross-Site Scripting (XSS) attacks present another serious concern for web applications, which usually occur when untrusted data often from user input is injected into your application. That's where data sanitization comes into play.

User input is a common attack vector and it may contain harmful code or scripts. A recommended approach to handle this and circumvent XSS attacks is to always sanitize user input using libraries like DOMPurify to remove detrimental content before rendering. This needs to be done for all user inputs, whether they're from forms or API requests. Don't rely on client-side validation alone, as it might be circumvented; opt for server-side validation, as shown below:

// pages/api/submit.js 
export default function handler(req, res) { 
    const { data } = req.body; 
    // Validate and sanitize data 
    if (!isValid(data)) { 
        res.status(400).json({ error: 'Invalid data' }); 
    // Process the data securely 
    // ... 
    res.status(200).json({ success: true }); 

In the code snippet above, server-side validation is used efficiently to validate and sanitize user input.

In conclusion, proactive error handling and thorough data sanitization are paramount for securing your Next.js applications. Remember, the objective is not solely about preventing errors or refining code functionality, but also about fortifying your application against persistent threats in the web development landscape.

Enhancing Application Security with Next.js Middleware

Next.js middleware is another powerful way to enhance the security of your web applications. Middleware provides custom route handlers and is often used as an escape hatch for cases that cannot be addressed with built-in functions offered by the framework. However, with this customization comes great responsibility as these custom handlers may also inadvertently create certain security risks.

The use of custom middleware allows developers to craft specific security rules that fit their application needs. Here's a simple example of a middleware function that prevents unauthorized access to a particular route.

import { NextApiRequest, NextApiResponse } from 'next'

export default function handler(req, res, next) {
    // Check if user is authenticated
    if (!req.isAuthenticated()) {
        // If not authenticated, send an error response
        res.statusCode = 401
        return res.end('Access denied')

    // If authenticated, call the next middleware or route handler

Given this added control and flexibility, it is vital to keep an eye out for possible security leaks. The misuse or inadequate use of such freedom can potentially open up security vulnerabilities, like unauthorized access to sensitive data or secured routes, or allowing unintended behaviours that can be exploited by malicious users.

While working with middleware, it's crucial often to question the security implications of any given solution. For instance, when creating a middleware function to authenticate users, is the authentication token verified and correctly scoped? When validating user input, are all potential types and forms of payloads considered? Such thoughtfulness in design can help you maximize the security benefits of using middleware in Next.js.


This article discusses security guidelines for Next.js applications, covering topics such as implementing HTTP security headers, protecting API routes, CSRF protection, error handling, and data sanitization. The key takeaways include the importance of incorporating HTTP security headers to mitigate common web threats, securing API routes with reliable authentication strategies, implementing CSRF protection and rate limiting, and handling errors and sanitizing user input. A challenging technical task for readers could be to perform a thorough security audit of their Next.js application, evaluating the implementation of security headers, authentication mechanisms, error handling, and data sanitization to ensure robust application security.

Don't Get Left Behind:
The Top 5 Career-Ending Mistakes Software Developers Make
FREE Cheat Sheet for Software Developers