What is black-box testing?

Black-box testing refers to any type of testing performed without prior knowledge of the internal workings of a system. In cybersecurity, the term black-box testing is used interchangeably with dynamic security testing and can cover a variety of testing techniques, from manual penetration testing to fully automated vulnerability scanning using dynamic application security testing (DAST) tools.

What is the role of black-box testing in application security?

The idea behind black-box testing in application security is to take an external attacker’s view of your security posture to find security vulnerabilities and misconfigurations in your running websites, applications, and APIs (application programming interfaces). This kind of outside-in application security testing is vital for many reasons, allowing organizations to:

• Get a realistic security assessment for their systems in the face of real-world attack techniques
• Find runtime security vulnerabilities that are not detectable through white-box testing at the level of source code, including misconfigurations, vulnerable tech stack components, and security issues resulting from interactions between various application components as deployed
• Maximize technology-agnostic security test coverage across their application environments

Why is black-box testing important for security?

Black-box security testing is an important part of any cybersecurity program and strategy. Combining automated security scanning with in-depth penetration testing by security experts gives you:

• An outside-in view of potential vulnerabilities and attack vectors, including issues that may not be detectable with other testing methods
• Broader coverage of your attack surface, including systems and dependencies that are not accessible to white-box testing
• Regulatory compliance in scenarios where your organization is required to use black-box methods in its security assessments and audits
• An independent third-party view of your security posture (when using external penetration testing services)

Differences between black-box testing and white-box testing

The main difference between black-box and white-box test methodologies is the level of knowledge of the system being tested. When treating the system like a black box, tests are performed by examining it from the outside without any knowledge of its internal workings. White-box testing, on the other hand, encompasses all tests performed with information about system internals.

In application security, black-box methods are usually understood to cover manual penetration testing and vulnerability scanning using DAST tools, while white-box security testing methods are those that encompass testing application source code (static application security testing aka SAST) and components (software composition analysis aka SCA). In practice, black-box and white-box approaches to application security are most effective when combined into a unified process that plays to the strengths of each methodology.

The distinction can also apply to different types of penetration testing, depending on the scope of a test and the level of information available to the penetration tester. While not as common as black-box pen testing and harder to set up as external testing services, white-box penetration tests can provide invaluable information about the effectiveness of existing security controls. Black-box penetration testing, on the other hand, is most useful as a security assessment measure that checks for gaps in the security process that may allow vulnerabilities to slip into production.

What is gray-box testing?

Gray-box testing falls somewhere between white-box and black-box approaches and is performed with some partial knowledge of the system under test. The name originates from a color mixing analogy: if you can’t see anything inside a black box but can see everything inside a white box, then mixing the two visibility levels in some proportion is like mixing black and white paint to give grey.

In application security, the term grey-box testing is synonymous with IAST (interactive application security testing). Depending on the product, you can think of IAST tools as either adding some dynamic insights to SAST or adding some code-level insights to DAST. Invicti and Acunetix are currently the only products that offer true DAST-driven IAST without requiring code instrumentation.

Pros and cons of black-box application security testing

PROSCONSTest any running system you need to, including legacy web apps and third-party softwareCan only test systems and endpoints that are already runnable and which are running and accessible during testingTechnology-agnostic for broader coverage and easier setup across websites, applications, and APIsOnly the most advanced dynamic security testing tools can fully crawl and test JavaScript-heavy applications and systems that require authenticationUse at any stage of the software development lifecycle (SDLC) where a runnable application is availableMay affect system performance if performed directly on production systemsGet fewer false positives and more actionable issues for remediation compared to static analysis tools

Using DAST tools for black-box testing

Dynamic application security testing tools are the mainstay of black-box test automation for security teams and ethical hackers working with web applications and APIs. Any DAST tool automates many time-consuming recon and testing operations for pentesters, but enterprise-grade solutions can also serve as standalone black-box security testing platforms. Best practices for building DAST into your black-box testing process depend on where in your SDLC you decide (and are able) to run DAST:

• Black-box security testing during development: Modern DAST tools can and should be integrated into DevOps workflows and CI/CD pipelines to test as early as possible, starting already with the first available application builds.
• Using DAST in staging and on pre-release builds: Modular applications only bring all their functionality together once deployed, making staging the most important stage for automated black-box testing with DAST.
• Black-box testing in production: When carefully fine-tuned, modern DAST is far less invasive than legacy tools, making it possible to scan in production on a regular schedule for a continuous security process. Wherever possible, it is still best practice to run any automated testing on cloned instances rather than directly on production environments.

To learn more about using DAST in your development pipeline, read the Invicti white paper Security at the Speed of Software: DAST in the SDLC.

Frequently asked questions about black-box testing