Protect Your REST APIs: 10 Security Mistakes You Didn’t Know You Were Making

Ramesh Fadatare

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4 min read

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Feb 8, 2025

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REST APIs are the foundation of modern web and mobile applications. However, poor API security can expose sensitive data, making your application vulnerable to attacks like data breaches, unauthorized access, and injection attacks.

In this article, we’ll cover 10 common REST API security mistakes and how to fix them with best practices. To demonstrate each mistake, we will use Java and Spring Boot examples.

For non-members, read this article for free on my blog: Top 10 REST API Security Mistakes and How to Fix Them.

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1️⃣ Exposing Sensitive Data in API Responses 🔓

❌ Mistake: Returning Passwords, API Keys, or Internal Data

Some developers accidentally expose sensitive information in API responses.

Bad Example: ❌

{
    "id": 1,
    "email": "user@example.com",
    "password": "mypassword123",
    "apiKey": "XYZ-SECRET-123"
}

✔ Risk:

• Hackers can steal credentials and gain unauthorized access.
• Exposed API keys can compromise your entire system.

✅ Solution: Use DTOs and Restrict Fields

Use Data Transfer Objects (DTOs) to control what data is returned.

✔ Good Example: ✅

public record UserDTO(Long id, String email) {}

@GetMapping("/users/{id}")
public UserDTO getUser(@PathVariable Long id) {
    User user = userRepository.findById(id).orElseThrow();
    return new UserDTO(user.getId(), user.getEmail());
}

✔ Best Practices:

• Never return passwords, API keys, or tokens in API responses.
• Use DTOs to expose only necessary fields.

2️⃣ Lack of Proper Authentication and Authorization 🔑

❌ Mistake: No Authentication