Even those familiar with penetration testing (pen testing) often find talk of pentesting “colours” – white box, grey box (or gray box), black box, etc. – very confusing. Before we provide clarity, let’s quickly revisit what pentesting is and why it’s important for your business.

A pentest is a type of intrusion test where a company audits itself (or outsources the effort to experts like Packetlabs) to discover its security flaws. Pentesting professionals (ethical hackers) deliberately attack the organization’s systems like a potential hacker to get deeper visibility into security gaps and help guide the organization’s cyber defence strategies.

Pentesting should be done at least once a year for maximum effectiveness. Only then can the company stay ahead of evolving threats and consistently secure its networks and systems.

With so many types of pentest options, which one should you choose: white box, grey box or black box?

And is a grey box pentest the best strategy?

What is a Grey Box Pentest?

Yes, pentesting is a very “colourful” area. But the different colours have specific meanings, which drive how that pentest is conducted and for what purpose.

In a black box pentest, the ethical hacker is provided with no prior information to guide their effort. In effect, they work in an “opaque” environment where they do not know the target system or source code. Since they’re essentially blind to all contextual or other cues, they must observe the system and create their maps and diagrams. Black box pentesting demonstrates how even a hacker with no inside knowledge could compromise a system and is considered the most authentic pentesting method.

At the opposite end of the spectrum is white box pentest. Here, the ethical hacker works within a “clear box” or “open box” because they have full access to the target system’s source code, network maps, credentials, etc. This test provides a comprehensive assessment of internal and external vulnerabilities and is best for simulating targeted attacks on specific systems by leveraging the maximum number of attack vectors. The cost is lower than a black box pentest since the tester already has relevant information to start and complete the test.

And finally – the grey box pentest. Just like the colour gray is a blend between black and white, a grey box pentest is a blend of white box and black box pentesting.  Here, the ethical hacker can partially see what’s in the box, which is why it’s also called a translucent box test. They have a limited amount of information about the target system, which they try to leverage to penetrate the system like a hacker. They may also have elevated system privileges.

Why a Grey Box Pentest is Often the Best Pentest Strategy

A grey box pentest is most beneficial to:

  • Simulate an insider threat
  • Test an application to check authenticated user access

In an insider attack, a user could damage the target system. Grey box pentesting can simulate this threat to understand the level of access a privileged user could gain to cause damage. It can also verify user authentications and check if a particular user can access another user’s data.

With a grey box pentest, testing speed is slightly quicker than a black box pentest since the tester more information. However, it makes up for this drawback with a broader and more efficient assessment of a target system’s security. Moreover, since testers are not entirely in the dark, they can simulate attacks more efficiently and go beyond what would be possible in the black box mode. A grey box pentest achieves a good balance between the efficiency of the black box method and the depth of the white box approach.

In the recent past, almost all high-profile cyberattacks have involved intelligent, persistent adversaries who took the time to conduct some reconnaissance on their target organization’s environment. This gives them practically insider-level knowledge and allows them to launch attacks larger in scope and scale than they would be otherwise. A grey box pentest strategy is often the best strategy in such scenarios since it delivers depth, efficiency, coverage, and authenticity.


The penetration testing strategy you choose would depend on the systems you want to test, your cybersecurity goals, and how much information you can provide to the tester. However, if you need a method that’s efficient, thorough and does not require time-consuming reconnaissance, choose grey box pentesting.

The Packetlabs penetration testing team comprises qualified and certified professionals who know what it takes to strengthen – and weaken – your organization’s systems. They find vulnerabilities automated tools and even other human testers overlook, and tailor their testing approach to your system requirements. They also create detailed reports, so the organization can quickly understand your security posture and prioritize efforts to strengthen it. For a free, no-obligation quote, click here.