Microservice architectures, public web services, system integrations, unified backends for web and mobile apps—all these things and more are made possible by APIs, or application programming interfaces. APIs are the backbone of modern web technologies but come with their own challenges and security risks, requiring as much (if not more) security testing as the user-facing parts of applications. Manual penetration testing can rarely keep up with the scope and speed of development, making API security scanners vital tools to maintain a baseline level of application security testing across API and GUI attack surfaces in between pentests.

What is API security scanning?

API security scanning involves automatically analyzing APIs to uncover vulnerabilities, misconfigurations, and compliance issues. This starts with discovering endpoints using various approaches and may include validating adherence to schemas defined in API specifications, but in-depth API vulnerability scanning is the most important capability to keep in mind.

While API security is often treated as a separate field of cybersecurity, it is an integral part of application security, so any vulnerability scanner you use for your web apps should ideally also cover your APIs. That way, scanning APIs doesn’t require separate tooling to uncover security issues in the underlying systems and applications, like having a REST API scanner for your REST endpoints, a web vulnerability scanner for your websites, and so on. Advanced DAST (dynamic application security testing) tools with API-specific features now exist that are able to simulate real-world attack scenarios across the entire application attack surface, including testing API endpoints and finding API-specific vulnerabilities.

The importance of API security scanning

Modern APIs are integral to the functionality and often the internal architecture of web applications, making them a significant attack surface. Compared to more visible graphical user interfaces, they tend to fly under the radar when it comes to asset inventory and testing—including security testing. Key reasons to prioritize API security scanning include:

• Protecting sensitive data: APIs are designed to provide automated access to application data and operations, which makes them a prime target for attackers going after sensitive information.
• Securing the underlying applications: While APIs can be targeted in their own right, they also provide an avenue to attack applications or systems that reside behind them, for example to access backend databases via SQL injection.
• Ensuring compliance: Cybersecurity standards, regulations, and frameworks now often mandate application vulnerability scanning and remediation, and these efforts must also cover APIs to be comprehensive.
• Finding forgotten or abandoned endpoints: Endpoints or entire APIs that have fallen out of use but remain accessible (shadow APIs) are a major vector for data breaches, making discovery features a vital part of API security scans.
• Maintaining security in between manual pentests: Manual testing has always been the dominant approach to API security testing, but any manual test will be less complete, more expensive, and slower to respond than automated security scanning, so both are needed.

Why API security testing needs special attention

Scanning APIs presents unique challenges compared to testing traditional web applications. This starts with scanning to find API definitions and endpoints in the first place because, unlike websites and web applications, APIs can’t be crawled to find test targets and determine their input parameters. Any API security scanner worth its salt should therefore cover multiple aspects of API discovery and testing, including at least:

• Support for major API types: REST is still the most popular API type, but the older XML-based SOAP is still in use and GraphQL is quickly gaining popularity. Supporting all the major types in one tool gives you maximum coverage and flexibility while also cutting down on the number of scanning tools and future-proofing your AppSec program in case engineering deploys a new API type tomorrow.
• Comprehensive discovery: Various API discovery techniques can be combined to identify undocumented APIs, deprecated versions, and exposed endpoints to find, test, and secure as much of your attack surface as possible. Methods can include finding API spec files, reading API information from container deployments, or reconstructing API specs based on traffic analysis.
• Support for API specification formats: There are even more spec formats than API types themselves, so scanners need to support as many as possible in order to ingest API information from all available sources. For REST APIs, this starts with YAML and JSON definitions as well as OpenAPI (Swagger) files, while GraphQL APIs have their own schema file format.
• Advanced authentication: Most APIs require authentication to access some or all their endpoints, making it vital for scanners to support standard auth technologies like OAuth 2.0 and JWT in order to perform authenticated scans in real enterprise environments. Without proper authentication, most API security scans will find few to no vulnerabilities, potentially leaving you with a false sense of security.

Best practices for API security scanning

To build and maintain a solid API security posture, organizations should make vulnerability scanning an integral part of their wider API and application security strategy. The following best practices will help you maximize security benefits from API vulnerability scanning:

• Use API discovery: Include APIs in a consistent and continuous discovery and security testing process that encompasses all your web assets. This helps normalize API security as a subset of application security and reduces the risk of undocumented or untested APIs making it to production (or remaining there).
• Integrate API scanning into DevOps: Build API security testing into your DevOps pipelines and the software development lifecycle by integrating application and API discovery and security testing with existing development tools and issue trackers.
• Streamline API vulnerability remediation: Make sure vulnerability reports from your API security scanner are accurate and actionable to help developers resolve issues efficiently. Where possible, API scanning should be part of the same toolchain as other AppSec tools.
• Centralize and enforce API management: Provide a process and inventory for API commissioning, versioning, modifications, and decommissioning. This lets your API scanner always work with the latest and most complete specifications while also reducing the risk of lingering shadow and zombie APIs.
• Define and update secure coding standards for APIs: The API scanning process should contribute to proactive security by incorporating lessons from security vulnerabilities and fixes into future development work.

The bottom line: API scanning is central to application security

APIs are an inescapable part of the web application landscape, both as external data interchange points and as a means of internal communication between software components. All too often, applications are deployed and updated far too quickly for manual security testing to keep up with the changes, and APIs are their most dynamic parts. Reliable and accurate application vulnerability scanners (DAST tools) are a vital part of any cybersecurity program—and to be truly effective, they also need to cover APIs.

As the only AppSec vendor, Invicti can help you with automated discovery and vulnerability scanning across your web applications and APIs alike, all on a single platform that integrates deeply into existing workflows and toolchains. Read more about how Invicti combines app and API discovery and security testing on one platform, and schedule a demo to streamline your application security testing—including your API security!