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Consider the following scenarios: a rogue employee may have plugged in a malicious USB stick, a phishing email may have been successful, or a cybercriminal may already be inside your network.
Internal network penetration testing answers that question. It simulates what a threat actor could do once past your external defenses, helping you find and fix hidden weaknesses before real attackers exploit them.
This guide will walk you through what internal pen testing is, why it matters, what it covers, and how to get started.
What Is Internal Network Penetration Testing?
Internal network penetration testing is a controlled, ethical hacking exercise that simulates an attacker with inside access to your network. Think of it as testing from the perspective of a malicious insider, a compromised employee laptop, or an attacker who has already breached your perimeter.
Internal testing explores your internal environment in great detail to find configuration errors, unpatched systems, and exploitable paths that could result in total domain compromise, in contrast to external penetration testing, which assesses your assets that are visible to the public online.
Why It Matters?
The majority of breaches do not begin with a hack straight out of Hollywood. They start with a foothold, such as a forgotten VPN portal or a phished credential, and then move laterally within the network.
Internal pen tests help you:
- Detect privilege escalation paths
- Discover weak or exposed credentials
- Validate segmentation and access controls
- Uncover dormant vulnerabilities in trusted zones
- Satisfy compliance requirements (PCI DSS, SOC 2, ISO 27001, etc.)
If you skip internal testing, you’re only securing the front door, while the windows and basement stay wide open.
What Internal Pen Testing Typically Covers
Here are some common areas tested:
- Active Directory Misconfigurations: Weak permissions, unconstrained delegation, and Kerberoasting risks
- Network Segmentation Flaws: Flat networks with unrestricted internal traffic
- Credential Reuse: Shared passwords across multiple services
- Outdated Software: Legacy applications with known exploits
- Sensitive Data Exposure: Unprotected shares, databases, or cloud drives
- Lateral Movement Vectors: Abused protocols and insecure configurations
A skilled tester will map your internal infrastructure, identify weak points, and simulate real-world attacks to validate risk.
Typical Methodology
While tools vary, here’s a high-level approach:
- Reconnaissance: Discover hosts, services, shares, and users
- Enumeration: Identify internal resources and potential targets
- Credential Attacks: Crack hashes or reuse leaked credentials
- Privilege Escalation: Gain elevated access through misconfigs or exploits
- Persistence Simulation: Demonstrate potential attacker footholds
- Reporting: Document findings with impact, evidence, and mitigation guidance
Signs You Need Internal Pen Testing
- Your IT infrastructure has recently been reorganised or expanded.
- You’re moving to hybrid or cloud environments.
- You’re working towards audits or certifications.
- Lateral movement paths are something you have never tested before.
- There are antiquated segmentation or legacy systems on your network.
Even well-staffed security teams often miss critical issues that require an attacker’s mindset to find.
Common Findings from Internal Pen Tests
- Domain Admin access via misconfigured GPOs
- Overprivileged service accounts
- SMB signing disabled across the network
- Sensitive documents stored in open file shares
- Stale admin credentials stored on end-user systems
These are not hypothetical. Bluefire Redteam regularly uncovers them during client engagements.
Next Steps: Secure the Inside
Internal network penetration testing is no longer optional. It’s foundational.
It’s time to conduct internal testing if you’re serious about knowing your actual risk exposure outside of the firewall.
Explore our Internal Penetration Testing Services or download our Internal Pen Test Readiness Assessment to assess your current gaps.
FAQs: Internal Penetration Testing
- What is the goal of internal penetration testing?To identify security weaknesses that could be exploited by insiders or attackers with internal access, before they lead to breaches.
- How is internal pen testing different from external testing?External testing targets internet-facing systems, while internal testing simulates attacks from within the network.
- How often should internal pen tests be performed?At least annually or after significant infrastructure changes, mergers, or compliance audits.
- Is internal pen testing required for compliance?Yes, standards like PCI DSS, SOC 2, and ISO 27001 recommend or require internal assessments.
- Can internal pen tests detect insider threats?Yes, they reveal how insiders or compromised devices could move laterally and escalate privileges.
- What is Internal Penetration Testing?
It simulates an attacker inside your network (e.g., malicious insider or compromised device). The goal is to identify how far they can go, what data they can access, and how to stop them.
- Do you test Active Directory (AD)?
Yes, AD security assessment is standard in Pro and Enterprise plans. We test for misconfigs, weak permissions, and escalation paths.
