White box testing, sometimes called open-book testing, provides penetration testers with complete access to internal system information that can include source code, architecture diagrams, administrative credentials, network topology, and other detailed documentation.
This pentesting approach enables the most thorough security assessment possible, as testers can analyse the target systems from multiple perspectives. With full visibility into how the application or system functions, pentesters can identify vulnerabilities in code logic, architectural weaknesses, and other security flaws that may be impossible to discover in the typical time that is allocated for an assessment.
This methodology is particularly valuable during the development phase of applications or before major product launches, as it catches security issues when they’re the least costly to fix – both in time, expense, and impact. White box testing is more time-intensive than other approaches but provides the highest assurance that critical vulnerabilities have been identified. It’s especially important for systems handling sensitive data, financial transactions, or healthcare information where security validation is essential.
Many organisations combine white box testing during development with periodic black or grey box testing in production to validate that security controls remain effective from both insider and outsider perspectives.