Grey Box Pen Testing: The Layer Most Teams Miss

hacker with stolen password-2

Most cyberattacks don’t begin with a sophisticated exploit or elite hacker wizardry. They usually start with something far simpler: a stolen password.

Maybe it came from a phishing email. Maybe it was found in a dump of breached credentials. Or maybe it was just a case of reused logins. But once someone has valid credentials—especially in environments with overly permissive access—the question quickly shifts from if they can cause damage to how much.

And yet, we still tend to fixate on keeping attackers out, not asking the tougher question: what if they’re already in?

That’s where Grey Box Pen Testing comes in. It’s designed to answer exactly that.

What Grey Box Testing Actually Looks At

In most security testing, we follow one of two routes:

  • Black Box Testing: No internal knowledge, simulating an outsider probing from the outside.

  • White Box Testing: Full access, simulating a security team doing an in-depth audit with full system context.

Grey Box Testing sits between the two. It reflects what happens when an attacker has some legitimate access—say, they’ve phished a staff member or bought their credentials online—but they still need to move laterally or escalate privileges to do real damage.

And that’s an increasingly common threat scenario.

A Quick Analogy

Think of your network like a secured office building.

  • Black Box is someone trying to pick the front lock.

  • White Box is giving someone the blueprints, keycards, and alarm codes.

  • Grey Box? That’s someone walking through the front door with a cloned employee badge.

Which of those is most common in the real world? And which gets tested for the least?

What Grey Box Testing Uncovers

When we run Grey Box tests we’re often looking for the same core things:

1. Credential Exposure and What Comes After

Credentials get compromised all the time. The real concern is what those credentials allow. With Grey Box testing, we map out how far someone can go with everyday access.

2. Overprivileged Accounts

“Permission creep” is real. Employees change roles, but their access sticks around. We often find standard users with legacy access to systems they shouldn’t have—and that attackers would love.

3. Privilege Escalation Paths

This is the jackpot for attackers. If they can jump from standard user to domain admin, it’s game over. Grey Box testing helps us find those escalation routes before someone else does.

What the Process Looks Like

Here’s how a typical Grey Box test plays out:

1. Start with Limited Access

We begin with standard user credentials—often linked to Active Directory—to reflect the kind of access a compromised employee account might have.

2. Internal Reconnaissance

We explore:

  • Shared folders
  • User roles
  • System access points
  • Network layout
3. Lateral Movement and Escalation

Can we move sideways across the network? Can we elevate privileges? Can we access sensitive systems?

4. Reporting Real-World Risk

Instead of listing every low-risk vulnerability, we write up the attack paths: how we got in, what we accessed, and what would have happened if it were a real attack.

 

Why These Trends Matter

Plenty of businesses do pen testing to check a box for ISO 27001, Cyber Essentials, or SOC 2. Fair enough.

But the reality is that attackers don’t care about your compliance schedule. They care about access. And they exploit weak credentials, misconfigurations, and flat internal networks long before you spot them in a once-a-year audit.

Grey Box testing closes that gap.

It shows you what an attacker could actually do today with a foothold—not what might happen in theory.

The Shift Toward Continuous Testing

Another thing worth mentioning: pen testing used to be expensive and infrequent. But with the rise of automation, that’s starting to shift.

There are now tools that allow us to run frequent, non-disruptive Grey Box tests using real credentials in real environments—without waiting weeks for a report or booking an expensive annual engagement. That means we can test continuously, and catch issues as they appear.

We’ve started building that into our own processes because it’s no longer enough to assume annual testing is enough. Attackers don’t wait 12 months between attempts.

Take Control of Your Security Posture

If you’ve only ever tested your perimeter, you’re missing a critical part of the picture.

Attackers are getting smarter, and credential-based attacks are only going to rise. Grey Box testing helps us see our network the way they would—with partial access, lateral movement, and escalation in mind.

It’s not about fear. It’s about clarity. The more you understand what your internal network actually looks like under pressure, the better decisions you can make to protect it.

If you found this article useful, you can sign up to receive more security insights, practical guides, and checklists like this—straight to your inbox.

Subscribe to the Newsletter Today!