Penetration testing is a simulated cyberattack used to uncover and exploit vulnerabilities in an organisation’s IT systems before real attackers do. Internal penetration testing, a subset of this, focuses on risks within the network perimeter.
The IBM Cost of a Data Breach Report 2024 reveals that compromised credentials were the most common initial attack vector, responsible for 16% of breaches. This highlights how frequently attackers gain initial access via internal pathways like stolen login details or phishing-based footholds.
Organisations must assess internal security just as rigorously as external defences to reduce lateral movement risk, protect critical data, and build resilience from the inside out.
What is Internal Penetration Testing?
Internal penetration testing is a security assessment conducted from within your corporate network to simulate an insider threat or a scenario where an external attacker has breached the perimeter.
Internal pen testing assesses compromised employee credentials, misconfigured systems, or vulnerable internal applications. It tests how easily a malicious actor, once inside, could move laterally, escalate privileges, and access sensitive data or systems.
Malicious insider attacks were the most expensive breach in 2024, costing $4.99 million on average.
External pen tests evaluate perimeter defences like firewalls or exposed services. Internal pen tests focus on threats within the firewall, such as unsegmented networks, weak access controls, and legacy system vulnerabilities.
Why Is Internal Penetration Testing Important?
Internal network penetration testing is important because many real-world breaches don’t stop at the firewall; they go beyond. Once attackers are inside, unsegmented networks, weak credentials, and misconfigured internal services create a fast lane to high-value assets.
In 2024, breaches involving compromised credentials incurred an average cost of $4.81 million and took 292 days to detect and contain, the longest of all attack vectors. In other words, internal threats not only hit harder—they linger longer. Internal pen testing prepares organisations to detect and contain such threats early, before the damage compounds.
How Internal Penetration Testing Works: Step-by-Step
The internal pen test process to simulate and evaluate internal attack scenarios. Here’s how it works:
1. Scoping and Goal Setting
Scoping and goal setting define the objectives, systems in scope, testing constraints, and success criteria. This first step determines if the test will simulate a rogue employee, a contractor with limited access, or a threat actor who breached the external defences. It is key to align goals with business impact and regulatory risk.
2. Network Enumeration
Network enumeration identifies active hosts, open ports, running services, and domain structures within the internal network. Testers use tools like Nmap and Netdiscover to map the digital terrain, which forms the foundation for vulnerability analysis. This helps them map potential attack paths just as a threat actor would. The longer a threat remains undetected, the greater the cost. Effective enumeration is your first line of defence in shortening that window.
3. Vulnerability Identification
Vulnerability identification spots weaknesses in unpatched software, misconfigured systems, or exposed services. These often represent the exact flaws that attackers exploit once they’re inside. Testers correlate identified issues with public CVEs to prioritise exploit paths.
4. Exploitation
Exploitation simulates real-world attacks to verify and leverage discovered vulnerabilities.
This may include exploiting SMB flaws, RDP misconfigurations, or exposed database services to gain unauthorised access.
5. Privilege Escalation
Privilege escalation involves moving from standard user access to administrative or root-level access. Testers try methods like DLL injection, token impersonation, or exploiting unquoted service paths to escalate privileges.
6. Lateral Movement
Lateral movement tests how easily attackers can pivot across systems and domains.
Techniques include pass-the-hash, SSH hijacking, and exploiting trust relationships between internal systems.
7. Reporting and Remediation Recommendations
Finally, reporting summarises findings, ranks them by severity, and provides clear remediation guidance.
Microminder Cyber Security delivers detailed, board-ready reports with proof-of-concepts, risk scoring, and tailored patching advice.
Key Tools Used in Internal Pen Testing
Internal penetration testing requires a combination of reconnaissance, exploitation, and post-exploitation tools to simulate real attacker behaviour and uncover hidden vulnerabilities within the network. These are the most effective tools used.
- Nmap – Used for network discovery and service enumeration. Nmap helps testers identify live hosts, open ports, running services, and operating system fingerprints. It forms the foundation for mapping internal network topology and prioritizing targets.
- BloodHound – Used to analyze and visualize Active Directory attack paths. This powerful tool uncovers hidden privilege escalation routes by collecting data on domain relationships, group memberships, and permissions, helping testers plan effective lateral movement.
- Responder – Used for capturing and relaying NTLM credentials via LLMNR/NBNS spoofing. Responder enables internal attackers to harvest credentials by impersonating legitimate services, making it ideal for testing insecure network protocols and poor segmentation.
- CrackMapExec – Used to automate SMB and Active Directory exploitation. Often described as a Swiss Army knife for internal networks, CrackMapExec facilitates credential validation, command execution, and lateral movement across Windows environments.
- Metasploit – Used for exploitation, privilege escalation, and post-exploitation. This framework allows testers to safely simulate real-world attacks, exploit known vulnerabilities, and assess the depth of compromise an attacker could achieve.
- Nessus/OpenVAS – Used for vulnerability scanning and risk identification. These tools scan for known CVEs, misconfigurations, outdated software, and insecure services — offering critical input to prioritize manual testing efforts and remediation.
Internal vs External Pen Testing
While both internal and external penetration testing serve vital roles in a comprehensive security strategy, their focus areas differ significantly.
| Feature | Internal Pen Testing | External Pen Testing |
| Attack Origin | Inside the firewall | Outside the network perimeter |
| Primary Goal | Simulate insider threat or post-breach scenario | Assess perimeter defenses and public-facing assets |
| Common Targets | Domain controllers, intranet apps, file shares | Web servers, email services, exposed APIs |
| Realistic Scenario | Rogue employee, compromised internal device | External hacker attempting initial access |
| Security Focus | Lateral movement, privilege escalation | Firewalls, access controls, application hardening |
How Often Should You Conduct Internal Pen Tests?
You should conduct internal penetration testing at least once a year or after significant infrastructure changes.
Trigger events include:
- A merger or acquisition
- Major changes in Active Directory or network segmentation
- New employee onboarding systems
- High-risk third-party integrations
- Following an actual security incident
Tip: Incorporating cyber tabletop exercises alongside internal pen tests to evaluate incident response effectiveness.
Best Practices for Internal Penetration Testing
The best practices for internal penetration testing include defining a clear scope, using real-world threat models, minimizing disruptions, combining testing methods, prioritizing remediation, involving certified experts, and integrating red and blue teaming. Here’s how to implement them effectively:
1. Define Clear Scope and Objectives
Before testing begins, clearly define the scope of the engagement. Focus on business-critical assets such as file servers, internal applications, databases, domain controllers, and sensitive endpoints. Align your testing goals with risk tolerance, compliance needs, and potential insider threats to ensure meaningful outcomes.
2. Use Current Threat Models
Leverage up-to-date attacker behavior frameworks like MITRE ATT&CK to simulate realistic internal threats. This ensures the test covers tactics such as credential dumping, lateral movement, privilege escalation, and data exfiltration — all commonly used in real-world breaches.
3. Minimize Operational Disruption
Internal pen tests can be intrusive. To prevent downtime, conduct tests in isolated environments or during off-peak hours. Coordinate with IT and security teams to ensure business continuity while enabling ethical exploitation.
4. Combine Automated Tools and Manual Techniques
Automated scanners can identify known vulnerabilities, but they often miss complex logic flaws, misconfigurations, and privilege abuse scenarios. Microminder Cyber Security’s internal penetration testing combines cutting-edge tools with expert-driven manual testing to uncover deep, context-specific risks.
5. Prioritize Remediation and Retesting
After testing, don’t stop at the report. Implement recommended fixes, then retest to validate that vulnerabilities have been properly addressed. Document all remediation efforts to support compliance and audit readiness.
6. Choose Experienced, Certified Testers
Internal testing requires deep knowledge of network architecture, Active Directory, endpoint configurations, and lateral attack techniques. Partnering with CREST and ISO 27001 certified professionals from Microminder Cyber Security ensures the test is ethical, safe, and delivers actionable results.
7. Integrate Red and Blue Teaming
Go beyond traditional testing by incorporating
red teaming (attack simulation) and blue teaming (defensive response). These exercises validate how well your internal teams can detect and respond to internal threats, a crucial component in zero-trust or hybrid environments.
Thank you. An expert will get in touch shortly 
