Grey box, white box and black box penetration testing: what’s the difference?

June 21st, 2022 Posted in Penetration Testing

What is Grey box, white box and black box pen testing?

When you have researched the best penetration testing services and have scheduled a pen test, part of the process will involve defining the scope of the pen testing engagement. There are different terms to describe whether the tester will be given access to your systems or given no prior information, known as white box, black box and grey box testing. Below, we will explore the difference between black box penetration testing, grey box pen testing and white box pen testing.

A penetration test is a point-in-time assessment of your company’s security posture. A suitably skilled tester will use a combination of manual and automated techniques to identify security weaknesses, such as technical flaws, software testing for vulnerabilities, flaws in source code, misconfigurations and business logic flaws.  

The penetration tester will exploit these vulnerabilities to mimic a would-be threat actor, simulating an attack on your systems.  

The penetration testing exercise is helpful for assurance and improving security defences. These tests find unpatched vulnerabilities and configuration problems in your infrastructure and applications and provide independent validation that your security defences are sufficiently resilient. 

Penetration testing approaches

A penetration tester can perform the test with or without prior knowledge of the client’s systems. When you schedule a penetration test, part of the process will involve defining the scope of the engagement; whether the tester will be given access to your systems or given no prior information.  

There are different terms to describe these methodologies, known as white box, black box and grey box testing. For organisations looking to conduct a penetration test, understanding the definitions of each is essential to ensure you are meeting your objectives.  

Below, we will explore each methodology in more detail. For further information on penetration testing, please read our guide to penetration testing here.  

What is white box pen testing?

With white box test techniques, the penetration tester is given explicit and extensive information about your IT infrastructure and/or target applications. This can include network architecture, information about servers and applications, endpoints, security controls, access permissions and so forth. This degree of information enables an in-depth and highly targeted test. The tester will identify and exploit as many vulnerabilities and threat vectors as possible without spending too much time on discovery and enumeration.  

While this makes for a valuable and comprehensive assurance exercise, one potential downside of white box testing is that the amount of information given to the tester might cause them to approach the exercise differently than a would-be, less-informed attacker, meaning that the focus may not be placed on the highest real-risk areas. However, white box testing is extremely valuable for testing during the development phase of new applications and infrastructure as part of a ‘security by design’ approach. 

What is black box pen testing?

Black box penetration testing is a method of testing where the penetration tester is given no prior knowledge of the target environment. They are tasked with discovering and exploiting vulnerabilities from a completely outside perspective, simulating an external attack as an uninformed attacker.  

While black-box testing could be called the most ‘authentic’ form of a simulated attack, it has drawbacks. Namely, attackers have unlimited time to devote to analysis and exploitation, while penetration testers are given a specific engagement period.  

This is why black-box testing is generally used for specific scenarios, and white-box and grey-box testing more broadly for penetration testing. The latter two enable testers to use their time more efficiently and focus on testing and exploiting systems, rather than discovering and analysing them.  

What is grey box penetration testing?

This type of testing technique is a hybrid of black and white box testing. In a grey box test, the tester is given some knowledge of the system’s internal structure but not as much information as in a white box test.  

As an illustration, the information provided could include login credentials for each level of account, a network diagram and a list of administrative users.  

The availability of this information allows the tester to use their time efficiently, improving their ability to detect and exploit vulnerabilities in a shorter amount of time and providing more granular recommendations.  

Advantages and disadvantages of the different penetration testing methodologies

White box, black box and grey box testing approaches have their own merits and are suitable for different exercises. It’s not a case that one method is better than the other. Instead, one methodology is better for a particular type of test.  

Broadly speaking, we can think of differences between the three in terms of speed, efficiency and accuracy.  

Black box testing tends to be the most realistic engagement type as the tester has less information and access, making for a closer to real-world, but potentially slightly longer, process. This lack of knowledge and no provided access also heightens the likelihood that some vulnerabilities may be missed – especially those within obscure areas of the estate. This, in turn, undermines the assurance exercise.  

Grey-box testing may be slightly quicker than a black-box test, but the additional information enables a more efficient test. The information provided to the tester also helps them better direct their testing efforts to discover valid and valuable weaknesses.  

White box testing may be the longest, and the most comprehensive. However, this depends on the focus of the test. While the amount of information may increase the length of the test as the tester may engage in activities such as code reviews, the high levels of access also mean that testers will be able to find an increased number of both internal and external vulnerabilities for remediation.  

What method is best for my business?

The methodology you go for will depend on the goals of your exercise. Generally, we advise most customers to conduct a white or grey box assessment if they are looking to gain assurance about the security of their systems.  

These tests tend to be more efficient and cost-effective for discovering security weaknesses than black-box tests. Grey box testing, in particular, is valuable for discerning the level of access a user could gain and exploit. Many companies will not go beyond white or grey box testing, content that their systems are well run and provide a generally good level of security. 

However, as noted, these tests don’t accurately reflect a real-world attack, whereby an attacker could come from any angle at any time and exploit security weaknesses in unexpected ways. It doesn’t test how people, processes and technologies work under stress and in the face of the unknown. 

For a more accurate test of real-world resilience, we call on the Red Team – a testing scenario that relies on a black-box methodology. The Red Team is a pen tester – or multiple pen testers – that simulates a real-world attack on your systems. They will typically have a loose goal, such as to gain access to an HR system or to extract a website’s underlying database but will be given free rein to do so however they can. 

The Red Team will start with very little information beyond knowing the given target, hence why this is a “Black Box” test. This forces the Red Team to act the same way as an attacker would, gathering information about the systems they’re targeting and identifying the weaknesses they can exploit, simulating a real-world attack. 

As a general rule, red teaming should be reserved for organisations that consider themselves to have a mature cyber security posture or a much larger attack surface that a capable adversary could exploit. If the organisation’s cyber security defences are weak, starting with a red team test makes little sense. Instead, the organisation should begin with white box and grey box assessments.  

How often should my organisation conduct penetration tests?

At a minimum, we advise that penetration tests should be conducted at least annually. They effectively act as a technical audit of your IT systems and applications, helping you to ensure that relevant security patches have been applied, any new software has been integrated safely, systems are configured properly, your operating systems aren’t vulnerable to attack, and your employees are following security protocols. 

Moreover, every time your organisation introduces a new application, website or service, it should be assessed with a penetration test. This is pivotal to secure development and ensuring that your security posture has not been negatively impacted by the introduction of new vulnerabilities. Note, that your penetration testing programme should be complemented by regular vulnerability scans – at least on a monthly basis.  

As your security posture becomes mature and regular penetration testing identifies fewer vulnerabilities, you can consider layering in red team assessments to understand the strengths and weaknesses in your security defences and culture that need to be addressed.  

Need a penetration test or just want some advice?

If your organisation needs help running a penetration test on an application or infrastructure, we’re here to help. We can assess your environment and run a full penetration test. We can also advise you on any follow-up actions or remediations from our findings. Contact us for a friendly chat.  

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Written by Alex Harper

Alex is a senior security consultant, specialising in security testing of IT infrastructure, web applications and mobile applications. He started his career as a software developer before moving into ethical hacking and security consulting. His qualifications include Cyber Scheme Team Leader (CSTL), Offensive Security Certified Professional (OSCP) and Qualified Security Team Member (QTSM).