Secure Next.js + React Apps: Prevent Injection Attacks with Proper Input Validation Using Yup and DOMPurify

In modern web applications, improper input validation remains one of the most critical and commonly exploited vulnerabilities. This issue arises when user-provided input is not properly validated, sanitized, or filtered before being processed by the application. Improper input validation is one of the most persistent security flaws, often opening doors to client-side and server-side attacks if left unaddressed.

Context and Impact

Improper input validation can lead to significant security risks depending on how user data is processed and stored. If user input is accepted without restrictions, an attacker may inject malicious scripts or unexpected payloads that can exploit the system. These attacks can lead to:

• Injection Attacks: Including SQL injection, command injection, or script injection.

• Authentication Bypass: Gaining unauthorized access by manipulating form inputs.

• Buffer Overflows: Causing memory corruption by supplying unusually large inputs.

• File Manipulation: Overwriting or accessing sensitive files through poorly validated upload/download mechanisms.

• Denial of Service (DoS): Causing performance degradation or application crashes through malformed or excessive input.

Best Practices and Remediation (Specific to Next.js + React with Yup)

In a Next.js React application that uses Yup for client-side validation, the following best practices are recommended to mitigate improper input validation risks:

• Client-Side Validation with Yup: Use Yup schemas to strictly validate form input fields. Ensure that inputs conform to the expected types, formats, and character lengths. For example, email fields should be validated using .email(), numbers can be range-checked using .min()/.max(), and string patterns can be enforced via .matches().

• Input Sanitization with DOMPurify in Yup: For inputs such as comments, names, or descriptions that accept free text, integrate DOMPurify into Yup’s .test() method to sanitize the content. DOMPurify helps remove or neutralize potentially harmful content such as:

  • Inline <script> tags

  • HTML event handlers (e.g., onerror, onclick)

  • Embedded JavaScript URLs (e.g., javascript:alert('XSS'))

  • <iframe>, <object>, and other suspicious HTML elements

  • Malformed or encoded HTML intended for injection

  Example Implementation (React Hook Form with Yup + DOMPurify)
  
  Below is a sample implementation that demonstrates how to combine DOMPurify with custom forbidden pattern checks in a Yup schema.

1. Validation Schema Setup (Yup + DOMPurify)
   


2. Using in a React Component (with React Hook Form + Yup)

This ensures only plain text or safe content is submitted, reducing the attack surface for cross-site scripting (XSS) and other injection vectors.

• Server-Side Validation: Reinforce all client-side checks with server-side validation. Inputs must be re-validated on the backend to ensure no bypass has occurred. Additionally, server-side sanitization should mirror or complement the client-side logic to maintain consistency and security.

By combining schema-based validation using Yup with content sanitization via DOMPurify, the application now effectively filters out potentially malicious input types that could have otherwise led to XSS, layout injection, or DOM manipulation attacks.

Conclusion

Improper input validation is a critical issue that should not be underestimated. In applications built with Next.js and React, adopting a layered approach to input validation—using Yup for schema validation and DOMPurify for sanitization—provides robust defense against injection attacks and other user input-related vulnerabilities. These best practices help secure application workflows and uphold user data integrity.

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