Penetration testing, or pen testing, can be categorised based on the amount of information given to the tester and the specific focus area of the assessment. It is a critical component of a comprehensive cybersecurity strategy, offering organisations a proactive way to evaluate and improve their defences. The main types include
black box, white box, and grey box testing, each providing unique insights into an organisation's vulnerabilities and attack surfaces.
In
black box testing, the tester has no prior knowledge of the system, simulating an external attacker attempting to breach the organisation without any internal assistance. This type of testing is often used to simulate real-world threat actors such as cybercriminals or hacktivists.
For instance, the tester might only be given a URL and would need to uncover vulnerabilities through a combination of reconnaissance and exploitation methods, such as subdomain enumeration, brute-force attacks on login forms, and code injection via poorly secured web forms or APIs. Black box testing emphasises the attacker's perspective and is particularly effective in testing how well an organisation’s perimeter defences can withstand intrusion attempts.
In contrast,
white box testing gives the tester complete access to internal documentation, source code, and system configurations. This level of visibility allows for a more thorough and comprehensive analysis, revealing flaws that a black box test might miss. White box testing is ideal for identifying complex issues such as logic errors, insecure coding practices, misconfigurations in authentication or authorisation mechanisms, and cryptographic weaknesses. Organisations often use white box testing during software development or major infrastructure overhauls, as it helps validate the robustness of internal security measures and is also useful for regulatory compliance and internal security audits.
Grey box testing strikes a balance between black and white box methodologies by providing the tester with limited or partial knowledge of the system. For example, the tester might be given user-level credentials or architectural diagrams, simulating a threat posed by a disgruntled employee or an attacker who has gained a foothold through a phishing campaign. This approach combines the realistic attack simulation of black box testing with the deeper analysis capabilities of white box testing. Grey box testing is particularly effective in evaluating access controls, privilege escalation paths, and the segmentation of networks or applications.
Beyond these classifications, pen tests can also be described as either external or internal. External penetration testing targets assets exposed to the internet, such as web applications, email servers, VPN gateways, and DNS servers. The goal is to assess how well these public-facing systems resist unauthorized access. On the other hand, internal penetration testing simulates an attacker already within the network, such as one who has breached physical security or compromised an insider account. This form of testing helps identify risks related to lateral movement, unauthorized access to sensitive files, and privilege escalation opportunities.
There are also specialized forms of penetration testing tailored to different layers of an organization’s infrastructure. Web application testing identifies common vulnerabilities such as SQL injection, Cross-Site Scripting (XSS), and insecure cookie configurations. Network testing evaluates infrastructure elements like firewalls, routers, and open ports, focusing on insecure protocols (e.g., Telnet, FTP) and improper segmentation.
Wireless testing assesses Wi-Fi networks for weaknesses like outdated encryption standards (e.g., WEP), rogue access points, and weak pre-shared keys. Social engineering testing goes beyond technical controls, emulating human-based attack vectors such as phishing emails, vishing (voice-based phishing), and physical intrusion attempts like tailgating or dropping malicious USB drives.
The pen testing process typically follows established methodologies such as OSSTMM (Open Source Security Testing Methodology Manual) or the guidelines provided by NIST (National Institute of Standards and Technology).
It begins with planning and reconnaissance, where testers and stakeholders define the scope of the engagement, establish rules of engagement, and gather initial intelligence using passive reconnaissance techniques such as WHOIS lookups, Google hacking, and public data mining. The next phase, scanning, includes network mapping and vulnerability scanning using tools like Nmap, Nessus, Nexpose, and Qualys. This phase helps testers identify live hosts, open ports, and known vulnerabilities.
Once vulnerabilities are identified, the exploitation phase begins. Testers attempt to breach systems using tools like Metasploit for automated exploitation, SQLMap for database attacks, or Hydra for password brute-forcing. After gaining access, testers may attempt to maintain access using persistent methods like reverse shells or establishing new user accounts, and often escalate privileges by exploiting misconfigurations or outdated software.
Finally, during the analysis and reporting phase, the findings are carefully documented, typically using standardised scoring systems like CVSS (Common Vulnerability Scoring System) to rank severity. Reports map technical vulnerabilities to business risks and include practical remediation guidance. These deliverables often include a detailed technical breakdown, an executive summary for stakeholders, and sometimes a live presentation or walkthrough of the findings and recommendations.
