Gray Box Penetration Testing: The What, Techniques, Benefits & Examples

What is Gray Box Pen Testing?

Gray box penetration testing is an application security testing method combining elements of white box and black box pen testing techniques. In gray box testing, the tester has partial knowledge of the system’s or application’s internal workings. This means they have access to some information about the system’s architecture, design, or code, but they do not have full knowledge of all its details.

Gray box security testing is often used when there is a need to verify specific functionalities or security vulnerabilities that may be challenging to identify with only black box testing. It bridges the gap between the limited knowledge of external behaviour and the detailed knowledge of the internal workings of an application or system.

Key Characteristics of Gray Box Testing:

Focused Testing: Gray box testing is often used to focus on specific areas or components of the system that are considered critical or high-risk.

Test Scenarios: Test scenarios are designed based on external behaviour (like black box pen testing) and an understanding of the system’s internal logic (like white box pen testing).

Test Data: Test data is selected to understand how the system processes information and interacts with its internal components.

Benefits: Gray box penetration testing can be more thorough than black box testing alone, allowing testers to target specific areas of concern. It also balances the complete knowledge of white box testing and the lack of knowledge in black box testing.

Gray Box  Pen Testing Example:

In testing a website form that triggers an email confirmation upon submission, a black box tester focuses on inputting valid and invalid email addresses without prior knowledge of the system’s internal workings to assess how the system responds.

In contrast, armed with the understanding that email validation relies on client-side JavaScript, a gray box penetration tester designs test cases to examine the system’s behaviour, adding depth to the testing process.

Furthermore, the gray box pen tester extends the scope by including a test case where JavaScript is intentionally disabled in the browser to evaluate how the system performs in this context. These testing approaches offer varying levels of insight into system behaviour and security.

What are the Steps Involved in Gray Box Penetration Testing?

  • Start by assessing what you already know about the system for gray box testing
  • Combine white-box and black-box testing methods to discover possible inputs
  • Consult the documentation to understand the expected outcomes for these inputs
  • Concentrate on the critical pathways within the system
  • Give special attention to vital sub-components
  • Determine suitable inputs for these sub-components
  • Define the expected outputs for these inputs in the sub-components
  • Create and run tests for each sub-component
  • Verify if each sub-component behaves correctly
  • Iterate these steps for all major sub-components

What Are Gray Box Testing Techniques?

Matrix Testing

Matrix testing involves creating a matrix representing various combinations of inputs, conditions, or scenarios to be tested. Testers use their partial knowledge of the software to identify critical paths and inputs that need thorough testing.

Matrix testing is beneficial when dealing with complex systems where multiple factors can influence the behaviour of the software. It helps ensure comprehensive coverage of various combinations of inputs and conditions.

Regression Testing

Regression testing is a gray box testing technique to ensure that new code changes or updates do not introduce defects or regressions into the software’s existing functionality. Testers may have partial knowledge of the code changes.

Regression testing is crucial in software development to maintain the quality and reliability of the application as it evolves. It helps detect unintended side effects of code modifications.

Pattern Testing

Pattern testing in the gray box testing technique involves identifying and testing specific patterns or structures within the code.

This type of evaluation can help identify the specific elements that led to defects, the strategies used for defect detection, and the effectiveness of the subsequent fixes. This knowledge can be used to identify and proactively address similar defects in future versions of the application or in new applications that share comparable structures.

Pattern testing is useful for verifying codebase coding standards, design patterns, or specific architectural elements.

Orthogonal Array Testing (OAT)

Orthogonal Array Testing is a systematic gray box testing technique used to test input parameter combinations efficiently. Built upon mathematical concepts, this technique reduces the number of test cases needed while maximizing test coverage.

OAT is especially valuable when dealing with software configurations with multiple parameters that interact with each other.

Authenticated Testing

Authenticated testing is a technique used in gray box testing to assess the security and functionality of a system with partial knowledge of its internal workings and access permissions. This technique involves testing a system while having limited access or privileges, often with the same level of access as an authenticated user.

In authenticated testing, testers log in or gain access to the system using valid credentials or authentication methods, just like authorized users would. This allows testers to interact with the system as an authenticated user would, which is crucial for assessing its behaviour in a real-world scenario.

What Sets Gray Box Testing Apart From Black Box And White Box Testing?

Gray Box Testing Black Box Testing White Box Testing
Testing Level Depending on the tester’s knowledge and objectives, it can be applied at various levels, including functional, integration, and system testing. Functional testing, higher-level testing (focuses on the software’s external behaviour). Lower-level testing (focuses on internal code structure and logic).
Tester Role Testers have partial knowledge of the internal code or structure.

Design test cases to target specific areas or components based on that partial knowledge.

Testers don’t need knowledge of the internal code or structure.

Focus on testing the software’s functionality, usability, and compliance.

Testers have in-depth knowledge of the internal code, algorithms, and data structures.

Design test cases based on code analysis and logic.

Skills Required Requires a balance of domain knowledge and some technical skills.

Testers should be able to use their partial knowledge effectively to design relevant test cases.

Requires strong domain knowledge and testing skills.

Less technical expertise is needed compared to white box testing.

Requires deep technical knowledge of programming languages, algorithms, and software architecture.

Testers need strong coding and debugging skills.

Cost Costs can vary depending on the extent of partial knowledge required.

It may require training and some technical resources, but generally less expensive than white-box testing.

Typically, the least expensive option in terms of training and resources.

Testers do not need specialized technical skills.

Generally, the most expensive option due to the need for highly skilled testers with in-depth technical expertise.

Requires access to the source code and specialized tools.

You can explore when to use each method on our detailed blog on black box vs. gray box vs. white box testing.

What are the Benefits of Gray Box Testing?

Enhanced Test Coverage: Gray box testing allows testers to design test cases that provide broader coverage than black box testing.

Uncover Hidden Defects: Testers can identify defects, vulnerabilities, or issues that might not be evident through black-box testing. This is especially valuable when internal code structure knowledge helps find potential weaknesses.

Efficiency: Gray box testing can be more efficient than white box testing in terms of resource and time requirements. Testers do not need to delve deep into the source code but can still achieve meaningful coverage.

Realistic Scenarios: Testers can simulate real user scenarios and interactions more effectively than black box testing, as they have some insight into how the application works internally.

What are the Limitations of Gray Box Testing?

Limited Knowledge: Testers have only partial knowledge of the internal code, which can be a limitation. They may miss certain critical issues or vulnerabilities that can only be uncovered through white-box testing.

Dependency on Documentation: Gray box testing often relies on documentation or informal knowledge sharing about the application’s internals, which may not always be accurate or up-to-date.

Complexity: Depending on the extent of the partial knowledge, gray box testing can be more complex to plan and execute than black box testing, and it may require specialized skills.


When deciding between black box, white box, and gray box penetration testing, it’s essential to consider several critical factors.

These factors encompass your testing timeline, adherence to security and compliance standards, the depth of analysis needed, the application’s complexity, the presence of additional security layers within your application, and your confidence level in your chosen pen-testing vendor.