How to Perform REST API Security Testing: Step-by-Step Guide

Quick Summary: REST APIs, being a critical component of modern digital infrastructure, must be secure to protect your data and applications. However, understanding how REST API security testing works is vital to perform the tests efficiently. This blog provides crucial information along with steps to test REST APIs for security.

In today’s digital sphere, REST APIs play a vital role in connecting disparate systems and providing smooth data exchange between them. While they are indispensable for seamless communication between services, hidden vulnerabilities can pose a serious challenge to the security and integrity of these APIs.

Attackers can take advantage of common API security flaws such as data exposure, misconfigurations, broken authentication, verbose responses, and more to attack APIs and steal data. You need to perform regular REST API security testing to tackle this challenge and keep your data safe. REST APIs testing enables you to uncover hidden loopholes and fix them before an attacker exploits them.

Now the question is – how to perform REST API security testing, and why is it important? This blog aims to answer these questions and others regarding security testing for APIs. So, let’s dive into this blog to secure REST APIs for your business.

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An Overview of REST APIs

REST (Representational State Transfer) is an architectural pattern to design APIs and networked applications. Many modern APIs are built on REST architecture. However, REST APIs are often susceptible to cyberattacks due to direct access to data and logic, weak authentication, lack of rate limiting, improper input validation, insecure third-party integration, and more.

Why is Security Testing for REST APIs Important?

REST APIs serve as a gateway to the core functionality and logic of an application or system. If your APIs are not secure, your application or system is not secure as well. The following are the key pointers that show why REST API security is important to build a strong security posture for your apps and systems.

Protect Sensitive Data

REST APIs usually handle sensitive data such as personally identifiable information (PII), credit card data, phone numbers, etc. Security testing for REST APIs helps identify and resolve potential weaknesses that may expose sensitive data. By testing your APIs for security, you get in-depth insights into the threat landscape and strengthen your security posture.

Prevent Issues from Frequent Changes

As applications update over time, APIs evolve with them. Consequently, new code changes are introduced that need to be tested for security. REST API security testing helps continuously test APIs in the development environment to identify issues with frequent code changes. This ensures secure APIs in production.

Address API-specific Vulnerabilities

Many common vulnerabilities specifically occur in REST APIs that can only be identified by testing them. Examples of API-specific vulnerabilities include unrestricted resource consumption, broken object-level authorization, broken authentication, and more. Hence, API security testing for REST APIs is vital to identify these vulnerabilities precisely and protect APIs from common attack vectors.

Insecure APIs Impact the Entire Ecosystem

REST APIs connect disparate systems and applications, creating an intertwined ecosystem. Due to interdependence among these components, a vulnerable API will render the entire ecosystem vulnerable to cyberattacks. Hence, API security is vital to protect not only the score of APIs deployed in your production environment, but also the systems and applications running on them. Insecure APIs will allow attackers to gain access to sensitive data after bypassing front-end controls.

Maintain Compliances

For many organizations, compliance with different standards and regulations is required. Especially, it is mandatory for organizations in the healthcare, finance, and government sectors. In this case, organizations that fail to comply with these standards and regulations are subject to penalties and strict regulatory actions.

Consequently, REST API security testing is pivotal to ensure compliance with these standards and regulations. By identifying and resolving potential REST API security issues, you can ensure that your organization aligns with compliance.

Implement Best Practices

API testing within SDLC enables developers to understand the common flaws and encourages them to write better code. Developers can follow the best practices by identifying the key weaknesses and knowing the critical issues that frequently arise.

What are the Common REST API Security Vulnerabilities You Must Address?

The following is a list of common vulnerabilities in REST APIs that you must search and address to protect your business against potential cyberattacks.

Broken Object Level Authorization

BOLA, or Broken Object Level Authorization, is a kind of vulnerability in which an API fails to verify whether a user can access a specific resource. Consequently, an attacker may get unauthorized access to sensitive resources. This allows the attacker to modify other users’ data by manipulating object IDs.

Broken Authentication

Broken authentication is a vulnerability in which the authentication mechanism is not properly implemented or has flaws. For example, password policies are weak, or multi-factor authentication is missing. That can allow an attacker to bypass the authentication layer and gain unauthorized access to sensitive data.

Excessive Data Exposure

REST APIs may usually return more data than required in a response, which could become a potential problem from a security point of view. These APIs often rely on the front-end to filter or hide excessive data. Excessive data exposure can reveal critical information that attackers can exploit to attack your systems or applications.

Missing Rate Limiting

In a common scenario, APIs will take a user request, process it, and provide an output. However, a bad actor can take advantage of it by engaging the API with excessive requests to disrupt the services. Consequently, the API is subject to security risks like DDoS or brute force attacks. This occurs due to rate limiting vulnerability, where no limit is defined for the number of requests a user can make in a single session.

Security Misconfiguration

Security misconfiguration arises when security configurations are not done properly or there are some loopholes in them. For example, verbose error messages, misconfigured CORS, unnecessary HTTP methods enabled, HTTP headers not secure, etc. These configuration issues can allow an attacker to overcome security mechanisms and misuse APIs for malicious purposes.

Injection Vulnerabilities

This is a type of API vulnerability that occurs when unvalidated or sanitized user input is processed in requests. An attacker can take advantage of this vulnerability to inject malicious commands or scripts. There are many kinds of security risks, like SQL injection, command injection, and more.

Improper Asset Management

When APIs in your digital landscape aren’t properly documented and managed, they turn out to be potential attack points. Outdated or deprecated APIs still operational in your digital landscape are a serious security gap that you must identify and address as early as possible. It protects against the threats of shadow or zombie APIs.

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The Full Process to Perform Security Testing on REST APIs

Let’s see the step-by-step process to perform security testing on REST APIs.

Step 1: Prerequisites

Before you initiate testing, there are some important steps that you need to take. Begin by understanding the API specs using Postman Collections or OpenAPI/Swagger docs. After this, discover all endpoints, including those that have been deprecated, besides all public and private endpoints. Further, collect authentication information such as JWTs, OAuth flows, API keys, etc. All these preparations will enable your AppSec team to run tests efficiently.

Step 2: Perform Testing

Start with API discovery to uncover zombie and shadow APIs that can compromise your security. After this, there are various checks and assessments that you have to perform to evaluate APIs. These checks and assessments will enable your AppSec team to discover potential loopholes and address them before they get exploited by attackers. They are:

• Authentication and Authorization Tests: Evaluate the authentication and authorization mechanisms of an API to identify any gaps in the validation of legitimate users. This API security testing will help ensure that users are properly validated, as well as that their access to certain resources is verified.
• Input Validation Testing: User inputs are prone to malicious content, and they must be validated for proper format, data type, and other attributes. Input validation testing helps identify weaknesses in this aspect to prevent possible injection attacks.
• Misconfiguration Testing: Misconfigurations are critical security vulnerabilities that leave your REST APIs wide open for cyberattacks. Testing your APIs for misconfigurations enables your AppSec team to identify issues that could allow an attacker to bypass security controls and access sensitive data.
• Rate Limiting Testing: This test helps identify the missing rate limiting and throttling functions to evaluate the susceptibility to excessive requests. It helps discover vulnerabilities that may allow attackers to launch DoS attacks by checking if the API allows unlimited login attempts.
• Business Logic Testing: Another crucial security test for APIs is business logic testing. This involves evaluating APIs for potential misuse, abuse of workflows, repetition of actions, and other flaws that attackers may take advantage of.
• Fuzz Testing: API fuzzing or fuzz testing is a kind of security assessment in which an API is fed with unexpected or random data to discover any weaknesses. For example, in the case of numerical inputs, it can be fed with large numbers, zero, or negative numbers to check the responses and find any security issues.

Step 3: Reporting and Remediation

Reporting is the summarization of the findings of the test, including the description of vulnerabilities, severity level, business impact, executive summary, and other essential information, along with displaying the vulnerabilities identified in a prioritized view. In addition to highlighting and prioritizing the issues, your AppSec team will also provide remediation steps to quickly address those issues.

Step 4: Retesting and Verification

Resting your REST APIs will help you verify that the issues have been resolved. If there are some vulnerabilities left, you can find and fix security flaws in the REST API.

Methods of REST API Security Testing

There are two methods for testing REST APIs as given below.

Manual Method

In this method, testing relies on human expertise, and your AppSec team will manually inspect APIs by manipulating and exploiting endpoints. This method is suitable for in-depth security assessment of your REST APIs, enabling your AppSec team to test for business logic flaws, authorization bypass, sensitive data exposure, and unexpected behaviors.

Pros:

• It helps discover more complex and contextual issues that automated tools may not detect.
• It can be used to identify flow-based and custom logic issues.
• There is flexibility in testing, and payloads can be customized.

Cons:

• Time-consuming and expensive.
• Specialized skills are required.
• Not better for frequent and large-scale testing.

Automated Method

Your AppSec team can leverage automated API pen testing or vulnerability scanning tools to quickly test APIs and identify critical issues in no time. These tools run automated tests on APIs by simulating real-world attacks. Automated tests can be static, which checks the source code for security issues, and dynamic, which involves testing APIs at runtime.

Pros:

• It offers faster speed and efficiency in security testing.
• It can be integrated into CI/CD pipelines for testing within the SDLC.
• There are initial costs, but it’s cheaper in the long term.
• It offers repeatable tests to continuously identify and resolve issues.

Cons:

• It struggles to detect business logic and contextual vulnerabilities.
• There is a possibility of missed vulnerabilities or false positives.
• The initial setup may be costly and time-consuming.
• Testing is limited to the tool’s capabilities.

Top Tools to Perform Security Testing on REST APIs

The following is the list of top REST API security testing tools.

ZeroThreat

A modern API security testing tool with cutting-edge features to test web apps and APIs for 40,000+ vulnerabilities. It dynamically tests apps and APIs by imitating real-world attacks and uncovers vulnerabilities with near-zero false positives. Built with a zero-trust model, the tool offers role-based access control to ensure secure scanning. With seamless CI/CD integration and AI-powered remediation reporting, ZeroThreat is ideal for fast-paced environments for quick testing and remediation. It is best suited for testing REST, SOAP, and GraphQL APIs. It uncovers various security issues, including the OWASP API top 10.

OWASP ZAP

ZAP or Zed Attack Proxy is another powerful API security testing tool that is open source and free. It offers both active and passive scanning to test APIs for vulnerabilities, including traffic manipulation and fuzz testing. ZAP allows you to create custom test scripts and seamlessly integrate into CI/CD pipelines. It is one of the top choices for automated web app and API security testing among the free options.

Burp Suite

As a professional-grade security testing tool, Burp Suite is a powerful solution with top-notch functionalities. It offers rich features, extensions, and testing capabilities to evaluate web apps and APIs by analyzing traffic to identify potential security loopholes. Equipped with multiple in-built tools like Intruder, Repeater, Sequencer, etc., it allows for in-depth assessment of injection flaws, misconfigurations, and other security issues.

42Crunch

42Crunch focuses primarily on shift-left security testing, allowing developers to identify and resolve security issues in real-time during the development phase. With static analysis of APIs in the development process through OpenAPI specs, it identifies common security loopholes in REST APIs. It also performs dynamic testing with random inputs. With 300+ security tests, it thoroughly analyzes APIs for potential weaknesses. It can also be easily integrated into CI/CD and offers real-time reporting.

Postman API Security

Postman’s built-in automated API security testing enables you to evaluate REST APIs for a wide range of security issues, including OWASP top 10. While it’s not a dedicated REST API security testing tool like the rest, it offers automated security assessments that help uncover critical security issues. It offers JavaScript-based security tests in its sandbox environment that check APIs for potential security loopholes.

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Final Thought

Securing your REST APIs isn’t a requirement; it’s an essential practice to keep your data and applications secure from cyberattacks. It enables you to proactively identify and address critical security issues and slam the door on attackers before they try to hack your applications or systems.

Moreover, choosing the right REST API security testing tool is vital to perform REST API testing efficiently. ZeroThreat stands out from other tools with its next-gen DAST capabilities and automated pen testing. It combines deep and accurate scanning with AI-powered capabilities.

With advanced vulnerability detection, MFA-based scanning, and comprehensive coverage of 40,000+ vulnerabilities, ZeroThreat allows you to secure your APIs. You can integrate it into a DevSecOps workflow to continuously test and resolve issues in real time.

Give it a try to see how it works.