What Is API Security Testing?

Application programming interfaces, or APIs, have become a primary attack vector for cybercriminals in recent years — making API security testing an essential part of modern cybersecurity programs. Early and frequent API security testing enables security teams to identify and remediate vulnerabilities that hackers often exploit, helping to improve the overall security posture of the organization and its web applications and services.

APIs have become the backbone of software architecture. APIs are protocols, tools, and definitions that enable software applications to share data and functionality. As a result, APIs are critical to integration, automation, and connection between diverse applications and services. As developers build new applications, they can use APIs to access data and functionality from existing software rather than building databases and functionality from scratch. This speeds development processes while resulting in more powerful software and interconnected systems.

As the usage of APIs has exploded in recent years, the number of attacks that target APIs has grown as well. Because APIs are involved in a vast majority of interactions between users and applications, they have access to a great deal of sensitive data and they facilitate core business functions — which makes APIs very attractive targets for threat actors.

Successful attacks on APIs may allow threat actors to gain unauthorized access to IT environments. This in turn may lead to security breaches, data exposure, operational disruption, financial losses, damage to an organization’s reputation, and the loss of intellectual property.

The stakes are high. API attacks can jeopardize an enterprise’s revenue, resilience, and regulatory compliance. However, most organizations don’t yet have the right controls and the full scope of API security capabilities in place to prevent them.

Cybercriminals frequently target vulnerabilities in APIs, such as those outlined in the OWASP API Security Top 10 list. API security threats to APIs fall into several categories:

• API abuse. Attackers frequently exploit flaws in development that allow APIs to be used for unexpected behavior and malicious outcomes such as data exfiltration.

• Vulnerability exploitation. Many APIs are created with vulnerabilities and flaws that hackers can exploit to gain unauthorized access to data or functions.

• Credential theft. Threat actors may use social engineering techniques to steal login credentials and to access privileged API keys that allow them to use and manipulate the API, posing as a legitimate user or administrator.

• Exploiting misconfiguration and unmanaged APIs. Because of rapid API proliferation, IT teams are not always aware of all the APIs in their ecosystem. Many APIs may be left unprotected, allowing threat actors easy access. Attackers may also take advantage of failure to properly configure API security settings. Misconfigurations include incorrect access controls, insecure default settings, and exposed sensitive information.

Through regular API security testing, security teams can identify and remediate flaws to prevent attackers from successfully exploiting and abusing APIs.

The objective of an API testing solution is to ensure that security requirements for the API have been met, including requirements for secure access, encryption, and authentication. To achieve this, tests send a variety of API requests to API endpoints, analyzing the responses to uncover any security vulnerabilities, unwanted behavior, or bugs in the code. These API requests are inputs that mimic the actions and attack vectors of would-be cybercriminals. The testing process should cover all parameters, authentication mechanisms, and business logic to uncover potential security risks.

Common API security issues identified during a security testing include inadequate access control, improper input validation, and unwanted data exposure. Tests also verify that JSON data is properly validated and sanitized to prevent injection attacks and data leaks.

The most common types of API security testing include:

• Dynamic application security testing (DAST): DAST tools test APIs in real time during runtime to identify security issues. By simulating real-time attacks, DAST methods can identify vulnerabilities like injection flaws, authentication issues, and data exposure that might only be uncovered during execution, rather than by examining the source code.

• Static application security testing (SAST): These tools scan and analyze the API’s source code, looking for patterns that indicate possible flaws and vulnerabilities. SAST methods may uncover vulnerabilities such as insecure coding practices or flaws that could lead to SQL injection and cross-site scripting (XSS).

• Penetration testing (pen testing): These manual tests are performed by security experts and simulate real-world attacks to discover vulnerabilities. Pen testing can uncover complex security issues that automated tools may miss.

• Fuzz testing (fuzzing): This testing technique sends malformed, unexpected, or invalid data inputs to the API, seeking to uncover vulnerabilities related to input handling. The objective is to identify inputs that may cause an API to crash or behave unexpectedly.

• Automated testing: Automated testing enables DevSecOps teams to continuously test APIs as part of the software development pipeline.

• Functional testing: This test verifies that an API functions as intended. While primarily aimed at ensuring performance, functional testing also helps improve security by identifying issues that could lead to vulnerabilities. Functional tests include testing various data formats for communication, including JSON formats, to ensure that the API parses and processes data according to the specifications.

API security testing should be performed as early in the software development lifecycle as possible, before APIs go into production. When testing in pre-production, DevSecOps teams should “shift left,” moving testing to the earliest possible stage in the DevOps workflow. This allows developers to identify and fix bugs when they are most familiar with the code they’ve written, rather than remediating issues several months later. With continuous integration (CI) and continuous development (CD), new versions of APIs may be released hourly or daily, making it imperative to perform API security testing before code reaches the end of the CI/CD pipeline.

AppSec (application security) teams should also perform API security testing in post-production to catch flaws such as production configuration issues that may be hard to detect during earlier stages.

Here are the general steps involved in API security testing.

• Definition of scope: Testing teams identify all the APIs to be tested, including all API endpoints.

• Tool selection: Teams may choose API security testing tools like Burp Suite, Postman, and open source solutions from GitHub for functional and security testing.

• Automation: Integrating automated testing into the CI/CD pipeline helps to ensure continuous attention to security.

• Manual testing: Manual tests are important because they can help to uncover complex security issues that automated tools may miss.

• Input validation: This step helps to prevent attacks like SQL injection and data exposure.

• Run a wide range of automated tests that simulate malicious traffic, including the OWASP API Security Top 10 threats.

• Discover vulnerabilities before APIs enter production to reduce the risk of a successful attack.

• Inspect your API specifications against established governance policies and rules.

• Run API-focused security tests on demand or as part of a CI/CD pipeline.

By implementing a robust API security testing program, organizations and their security teams can:

• Enhance security posture: Regular testing enables teams to identify and mitigate security vulnerabilities to reduce the attack surface and minimize the risk of security breaches in cyberattacks.

• Ensure compliance: Testing helps to ensure compliance with security standards and regulations.

• Improve functionality: Regular testing can discover issues that could negatively impact an API’s performance and functionality.

• Reduce false positives: Automated testing tools help to minimize false positives, allowing security teams to focus on real issues.

• Faster remediation: Testing frequently enables earlier detection of vulnerabilities, allowing for quicker remediation.