How to Secure A Rest API
Tags: api, security, restapi, webdev
Published: 2023-09-05 12:16:43

In today's interconnected(As of My opinion it's "Internet Connected") world, REST (Representational State Transfer) APIs have evolved from being a mere buzzword to the lifeblood of modern software development. I hope, you already have a good understanding of what REST APIs are and how they work. However, even for the seasoned developer, the paramount importance of securing these APIs cannot be stressed enough.

## What is REST API?
As a quick recap, REST APIs are a set of architectural guidelines and conventions for building and interacting with web services. These APIs adhere to the principles of REST, a concept introduced by Roy Fielding in his seminal 2000 dissertation. Leveraging the ubiquitous HTTP protocol, REST APIs enable systems to exchange data and functionality seamlessly, making them indispensable in today's software landscape.

## What are use cases of REST API?

1. **Mobile Applications**: REST APIs are the linchpin that facilitates communication between mobile apps and server-side databases and services. This facilitates crucial functionalities like user authentication, data retrieval, and real-time updates.

2. **Web Applications**: Modern web applications often heavily rely on REST APIs to fetch data from servers, enabling dynamic and responsive user experiences.
 
3. **IoT (Internet of Things)**: REST APIs play a pivotal role in connecting IoT devices to cloud services, facilitating real-time monitoring, remote control, and data analysis.
 
4. **Third-Party Integrations**: Businesses leverage REST APIs to open their platforms to third-party developers, fostering innovation and expanding their reach through integrations with various services.

## How attacker attack or exploit vulnerabilities in REST API?

**1. Reconnaissance Phase:**

- **Target Identification**: Attackers identify potential targets by scanning the web for exposed APIs, typically searching for endpoints or known API documentation.

- **Endpoint Enumeration**: They attempt to discover all available API endpoints, as each endpoint represents a potential entry point for exploitation.

 **2. Exploitation Phase:**

**a. Injection Attacks**:

- **SQL Injection**: Attackers try to manipulate SQL queries through input fields, potentially gaining unauthorized access to databases or exfiltrating data.
- **XPath Injection**: When XML-based communication is used, attackers attempt to manipulate XPath queries, which can lead to unauthorized data retrieval or even XML entity expansion attacks.
- **Command Injection**: Attackers seek to execute arbitrary commands on the server by injecting malicious code through input fields.

**b. Authentication and Authorization Bypass**:

- **Brute Force and Credential Stuffing**: Attackers may attempt to guess or reuse passwords to gain unauthorized access to user accounts or administrative interfaces.
- **Session Hijacking**: If session tokens are not adequately protected, attackers may try to steal or manipulate them to impersonate legitimate users.
- **Inadequate Access Control**: Attackers may exploit poorly defined or implemented authorization mechanisms to access sensitive resources or functions they shouldn't have access to.

**c. Cross-Site Request Forgery (CSRF)**:

Attackers create malicious web pages or send malicious links to trick users into executing actions on a different site without their consent.

**d. Cross-Site Scripting (XSS)**:

Attackers inject malicious scripts into web pages viewed by other users, potentially stealing user information, session tokens, or redirecting users to malicious sites.

**e. API Rate Limiting and Denial of Service (DoS)**:

Attackers can overwhelm the API by making a large number of requests, causing it to become unresponsive or slow for legitimate users.

**f. Insecure File Uploads**:

Attackers may attempt to upload malicious files to the server, which could lead to arbitrary code execution or other vulnerabilities.

**3. Evasion and Anonymity:**

Attackers often use techniques to hide their identity, such as anonymizing proxies, VPNs, or the Tor network, making it harder to trace their actions.

**4. Persistence**:

Attackers aim to maintain access to the compromised system or data for as long as possible by creating backdoors, implanting malware, or manipulating configurations.

**5. Data Exfiltration**:

Once inside the system, attackers try to exfiltrate sensitive data, often by encoding it or disguising it within legitimate traffic.

Additionally, there are several crucial areas for attack where attackers always keep a watch on.

1. URL Path
2. User Token
3. Payload
4. Query Strings

### How to Secure REST API if you are a developer?

**1. Validate the User Using the Token Against the Token:**
When a user or client sends an authentication token (e.g., JWT) with a request, always validate it to ensure it matches the user associated with it. This prevents unauthorized access and ensures the request is coming from a legitimate source.

**2. Do not accept input directly from the browser; instead, validate and polish it.**
 User inputs, especially from browsers, should never be trusted. Always validate and sanitize user inputs to prevent potential security vulnerabilities like SQL injection or Cross-Site Scripting (XSS).

**3. A Request/Response Schema Validator Should Always Be Used:**
Implement request and response schema validation to ensure that the data exchanged between clients and your API adheres to predefined structures. This guards against unexpected or malicious data.

**4. Sending passwords or API keys to the front end is not recommended:**
Sensitive information like API keys and passwords should never be sent to the client-side code (frontend). Keep these secrets on the server-side to prevent exposure and potential misuse.

**5. Make sure the error message doesn't provide hackers with any hints:**
Avoid revealing sensitive information in error messages. Provide generic error messages to users while logging detailed errors on the server side. This helps thwart attackers' efforts to gain insights into your system.

**6. Follow the principle of least privileges or deny by default:**
Adopt the principle of least privilege, which means granting the minimum necessary permissions to users or services. By default, deny access to resources and only allow specific, authorized actions.

**7. Role-Based Access Control for API Implementation:**
Define roles and permissions for users or client applications. Specify which roles can perform particular actions and access specific resources. This approach enhances security by controlling who can do what.

**8. Create the Resources in JSON or YAML and begin implementing them:**
Represent your API resources and configurations in standardized formats like JSON or YAML. This simplifies management, version control, and documentation.

**9. Use intelligent rate limiters:**
Implement rate limiting mechanisms to control the number of requests a client can make within a specific time frame. Smart rate limiters adapt to the client's behavior and help protect against abuse or DoS attacks.

**10. Only allow HTTPS traffic:**
Ensure that all communication with your API occurs over HTTPS (TLS/SSL). This encrypts data in transit, preventing eavesdropping and man-in-the-middle attacks.

**11. Implement an API Risk Assessment:**
Regularly assess your API's security posture by identifying potential risks and vulnerabilities. This includes reviewing code, configurations, and dependencies.

**12. API keys, hashing keys, and other secrets shouldn't be included in code:**
Avoid hardcoding sensitive information, such as API keys or hashing keys, directly into your codebase. Instead, store these secrets securely in environment variables or configuration files.

**13. Implement Strong Authentication and Authorization**: Ensure robust authentication mechanisms like OAuth 2.0 or API keys, and implement fine-grained authorization controls.

**14. Input Validation and Sanitization**: Validate and sanitize all input data to prevent injection attacks.

**15. Rate Limiting and Throttling**: Implement rate limiting to mitigate DoS and brute-force attacks.

**16. Content Security Policy (CSP)**: Use CSP headers to mitigate XSS attacks.

**17. Regular Security Audits**: Periodically audit your API for vulnerabilities and conduct penetration testing to identify weaknesses.

**18. Monitoring and Logging**: Implement real-time monitoring and comprehensive logging to detect and respond to suspicious activities promptly.

**19. Security Patching**: Keep software and libraries up-to-date to mitigate known vulnerabilities.