Grey box penetration testing represents a middle ground between black box and white box approaches, where penetration testers are provided with partial knowledge of, or access to, the target system(s).
This typically includes being provided with user credentials, basic architecture documentation, or API specifications, but wouldn’t include full source code access or administrative privileges. This approach balances the realism of black box testing with the efficiency and thoroughness of white box testing, allowing testers to focus their efforts on finding meaningful vulnerabilities rather than spending excessive time on initial reconnaissance.
The grey box approach is often considered the most practical for real-world security assessments. It replicates scenarios where an attacker has gained initial access (for example, through phishing) or where a malicious insider with standard user privileges might initiate an attack. By providing limited information upfront, organisations enable testers to achieve deeper coverage within a reasonable timeframe, uncovering vulnerabilities that might remain hidden in a purely black box assessment.
This methodology is particularly effective for web applications, APIs, and internal systems where understanding basic functionality helps pentesters identify complex logic flaws and authorisation issues that automated tools would miss.