You’re Only Testing Half the Attack Surface

Many organizations run external penetration tests. It’s expected. It satisfies compliance requirements. It checks a box and results in a clean report.

Here’s the issue: Most attackers don’t stop at the front door. They phish credentials, exploit internal systems, escalate privileges, and move laterally. Once they’re in, the real damage begins. That’s why internal penetration testing is critical—and it’s what most organizations are missing.

Compliance Is a Baseline, Not a Strategy

We see this all the time. A company runs annual external tests, scans internet-facing systems, and addresses a few vulnerabilities. On paper, things look fine. However, none of that tells them what happens if an attacker gets inside. It doesn’t test segmentation, reveal privilege escalation paths, or expose shared credentials and legacy systems. Internal testing does. That’s where the actual risk hides.

External vs. Internal: What’s the Difference?

External Pen Test Internal Pen Test
Simulates An attacker on the internet targeting your public-facing systems*

An attacker who has already gained access (e.g., via phishing, stolen credentials, or insider threat)
Focuses On External exposed IP addresses for vulnerabilities and exploitable systems

Lateral movement, privilege escalation, internal systems, and data access
Common Goal Find vulnerabilities that could allow someone to gain a foothold from outside your organization

Understand what damage could be done post-breach and how well internal defenses hold up
Compliance Requirement      Often required (e.g., PCI, HIPAA)

Less commonly required, but critical for risk

Note: Web apps can also be tested; to ensure a robust assessment a dedicated application-layer testing, which focuses on specific areas beyond the scope of an external network penetration test is required.

Why You Need Both

External tests show how attackers get in; internal tests show what happens next. Combined, they provide a full picture of your organization’s exposure. Want a breakdown of what kind of penetration testing is right for your organization? We’ll walk you through it.

Real-World Example: What We Found

A regional healthcare client had never performed an internal pentest. Although their external results looked strong, once inside the network, we uncovered serious risks.

We were able to:

  • Move laterally between departments

  • Access sensitive health records

  • Escalate to the domain admin

  • Disable detection tools without alerting anyone

All of this was easily remediated, but only because it was discovered through internal testing.

If You Only Test the Outside, You’re Guessing

Most security teams understand that breaches can and do happen. That’s why detection and response capabilities are a priority. But without testing the internal environment like a real attacker, you’re relying on assumptions.

Internal penetration testing helps answer key questions:

  • Are segmentation and security controls working?

  • What happens after a phishing attack or credential theft?

  • How quickly can an attacker escalate and move?

  • Will your tools detect the behavior?

Want to simulate a real-world attack safely? Our breach and attack simulation platform, BlindSPOT,  is purpose-built for that.

What to Do Next

External tests meet compliance needs. But paired with internal testing, you now have the full picture. If you’re serious about protecting what matters, it’s time to test your assumptions, before an attacker does.

Let’s schedule a discovery call and talk about what an internal pentest would look like for your environment.

 

Strengthen your cybersecurity maturity by combining penetration testing with threat detection and response validation. 

 

Penetration testing is a foundational cybersecurity practice. It helps organizations identify exploitable vulnerabilities, validate prevention controls like firewalls and antivirus, and satisfy the expectations of compliance frameworks, cyber insurers, and board stakeholders. But in today’s threat landscape, pentesting only tells part of the story. 

Pentests answer questions like: 

  • Can a threat actor get in? 
  • Where are the gaps in our perimeter defenses? 
  • What vulnerabilities should we prioritize for remediation? 

What they don’t answer is: 

  • Will our tools detect an attacker once they’re inside? 
  • Will our SOC, MDR, or NDR teams respond in time? 
  • Are our detection and response investments actually working? 

This is where OnDefend’s Breach and Attack Simulation platform, BlindSPOT’s Threat Detection and Response Validation comes in—and why pairing it with OnDefend’s penetration testing services creates a more complete and proactive security strategy. 

 

Penetration Testing vs. Threat Detection and Response Validation: 

Pentesting checks your locks—on doors and windows—to ensure your house is secure from outside entry. But it doesn’t test every lock, every day. And it doesn’t tell you if your alarm system works, if each sensor works, or whether anyone responds when it goes off. 

Threat Detection and Response Validation does just that.  It simulates real-world attacker behaviors to validate whether your detection tools (EDR, SIEM, NDR) and response teams (internal SOC or third-party MDR/NDR/MSSP) detect, escalate, and respond in real time. 

 

Why Threat Detection and Response Validation Matters 

Modern cybersecurity assumes breach is inevitable. That’s why mature security programs focus not just on keeping adversaries out—but on how quickly they can detect, contain, and recover from an intrusion. 

BlindSPOT adds that missing operational visibility: 

 

  • Threat Response Validation: Measures your actual Mean Time to Detect (MTTD) and Mean Time to Respond (MTTR), benchmarking both tools and response teams against expectations and SLAs 

 

  • Alert Monitoring: Notifies you when a detection fails or a response is delayed—so issues are caught before an attacker takes advantage. 

 

Why Both Are Better Together 

You wouldn’t run a business with only a financial audit—you also track performance metrics in real time. Security should work the same way. 

  • OnDefend’s Penetration Testing validates perimeter security and identifies vulnerabilities before attackers do. 

 

  • Threat Detection and Response validates whether your internal and external detection and response controls are functioning as expected. 

 

  • Together, they provide a full-spectrum view of your readiness and resilience. 

That’s how you move from a reactive security posture to a proactive, mature one. 

 

Want to Learn More? 

BlindSPOT‘s new Threat Detection and Response Validation features are available in both our BAS platform and as a fully managed service. These features can also be bundled with OnDefend’s expert-led penetration testing. 

Whether you want to run it yourself or just get the outcomes, OnDefend can help you: 

  • Find gaps in prevention and detection before attackers do 
  • Hold vendors accountable to their SLAs 
  • Translate technical findings into board-level risk conversations 

Learn more at ondefend.com/blindspot