White Box Penetration Testing: Essence, Importance, Methods

White box penetration testing, also known as "clear box" or structural testing, is a type of penetration testing where the tester is given access to the internal workings of software or IT infrastructure to simulate hacker actions and find potential vulnerabilities.

Unlike "black box" or "gray box" testing, "white box" testing involves providing the tester (ethical hacker) with complete data about the network and system, allowing them to dig deeper and find hidden security flaws. White box penetration testing is typically used to examine core system components, especially in companies that develop their own products or integrate multiple applications.

Advantages of White Box Penetration Testing 

• The most comprehensive analysis of internal and external vulnerabilities from an internal perspective, which is not available to typical attackers.
• Ability to identify potential weaknesses in areas inaccessible to "black box" testing, such as source code, design, and business logic of the application.
• Availability at early stages of development when no user interface exists, which is not relevant for other types of penetration testing.
• Ease of automating test cases, which reduces the time and cost of penetration testing.

Methods and Criteria of White Box Penetration Testing

When it comes to software security testing, "white box" penetration testing involves examining source code to find vulnerabilities that could make the application susceptible to cybersecurity threats. The main aspects to be checked include:

Branch Coverage
A branch is one of many execution paths that code can take after processing a decision statement, such as an if statement. Branch coverage checks whether all branches in the codebase are exercised by tests and that no branch leads to anomalous application behavior.

Path Coverage
A path is an execution flow that follows a set of instructions. Path coverage examines all possible program paths and ensures that each path is traversed at least once. Path coverage is much more powerful than branch coverage and is useful for testing complex builds.

Statement Coverage
Statement coverage evaluates whether each line of code is executed at least once and helps find unnecessary or missing lines.

In addition to the three metrics above, white box penetration testing can rely on the following criteria:

• Control flow testing
• Data flow testing
• Decision coverage
• Condition coverage
• Modified condition/decision coverage
• State machine coverage

Stages of White Box Penetration Testing 

An approximate process of white box penetration testing of software may look as follows:

• Source Code Review. The first step involves understanding the internal functionality of the target application. At this stage, the test engineer studies the source code of the target software to lay the foundation for creating targeted test cases that will help identify security flaws.
• Test Creation and Execution. The tester creates test cases and executes them to find vulnerabilities in the software source code. Application testing can be either manual or automated.
• Report Generation. In conclusion, the tester creates a report with all the steps and strategies used and delivers the results of the entire testing process to the client.