What is Internal Penetration Testing: Methods, Tools, & Checklist – Source: securityboulevard.com

Internal penetration testing is a proactive approach that identifies vulnerabilities from within your network, allowing you to prioritize weaknesses and mitigate risks before they can be exploited. Understanding the methodology, steps, tools, and best practices involved in internal penetration testing is essential for establishing a robust security posture and protecting sensitive assets.

💡This Guide is part of our extenstive guide on penetration testing.

What is Internal Network Penetration Testing?

Internal network penetration testing is a cybersecurity exercise simulating a malicious attack launched within an organisation’s network.

The goal is to identify and exploit vulnerabilities that could be used by disgruntled employees, compromised accounts due to social engineering, or external attackers who have gained unauthorised internal access.

Why is Internal Penetration Testing Important?

Internal testing provides a crucial perspective on an organisation’s security. It won’t be wrong to say that a thorough internal penetration test offers the closest possible picture of cyber hygiene in an organisation. A few main factors include:

• Uncovers Insider Threats: It highlights risks posed by accounts of employees or contractors who may intentionally or accidentally cause damage.
• Reveals Hidden Vulnerabilities: Internal penetration testing exposes blind spots that external testing might miss, such as active directory security policy issues, weak passwords, outdated software, patching practices, information storage practices, or misconfigured systems.
• Evaluate Real-World Impact: Demonstrating how attackers can move within the network quantifies the potential damage a breach could cause.

Key Focus Areas of Internal Network Pen Tests

• Systems and Applications: Testing the security of operating systems, databases, and critical applications.
• Network Infrastructure: Evaluating the security of firewalls, routers, switches, security devices, and other network devices.
• Security Policies and Practices: AnalysiAnalysing directory group policy security settings, password policies, Kerberos security, auditing configuration, access controls, and incident response procedures.

• Data Exfiltration: Assessing the ability of an attacker to steal sensitive data.

Goals of performing internal infrastructure pentest

Internal pen testing delivers multiple objectives for a business and provides strategic input to the stakeholders. These include:

• Measures Insider Threat: Evaluate the potential for successful exploitation by malicious insider or compromised accounts.
• Assesses Security Controls: Provides a realistic, accurate picture of the effectiveness of existing security measures.
• Reveals Third-Party Risks: Simulates attacks to determine the extent of third-party/partner access to sensitive resources.
• Identifies Strategic Issues: Uncovers vulnerabilities related to data exfiltration, leaks, and system misconfigurations.
• Demonstrates Security Commitment: Shows active dedication to cybersecurity best practices, essential for clients and stakeholders.
• Shapes IT Strategy: Guides future IT investments and priorities by highlighting critical risk areas and potential security weaknesses.

Internal Vs. External penetration testing

Internal and external penetration tests offer complementary insights into an organisation’s posture. Internal penetration testing simulates attacks from inside the network, mimicking the actions of a malicious employee, contractor, or partner. Iscrutiniseses internal security practices, password strength, data handling, and the potential for lateral movement once inside the system. Conversely, external penetration tests target internet-facing assets like web servers and firewalls, replicating the tactics of an external hacker. External tests expose vulnerabilities in the network perimeter but provide a limited view of the internal security landscape.

Conducting annual internal and external penetration tests is ideal for the most comprehensive cybersecurity assessment. This dual approach allows for identifying and remedying vulnerabilities from within and outside the organisation’s risk of a successful breach.

Steps to Perform Internal Penetration Testing

Cyphere’s internal pentest approach consists of 6 phases with multiple steps based on test cases and the customer’s environment. Here is the detailed activity discussing steps in individual phases:

Phase 1: Pre-Engagement

• Scope: Define target network segments, subnets, VLANs, critical systems (domain controllers, file servers, sensitive databases, etc.), and any sensitive areas to avoid disruption.
• Rules of Engagement: Clarify permitted actions (e.g., exploitation, brute-forcing), off-limits tactics, and communication procedures during sensitive tests.
• Access: Determine tester accounts (domain, local admin), secure VPN or jump-box access, and necessary software/tools.

Phase 2: Reconnaissance

• Network Mapping: Document IP ranges, hosts, operating systems, open ports, and running services (SNMP, SMB, RPC, etc.)
• Active Directory Mapping: Enumerate domain structure, OUs, user accounts, groups, trust relationships, service accounts, and identify stale or privileged accounts.
• Peripheral Discovery: Scan for printers, MFPs, network-attached storage (NAS), IoT devices, IP cameras, building control systems, etc.

Phase 3: Vulnerability Identification

• Infrastructure Vulnerabilities:

  • Outdated OS/firmware (servers, switches, routers, printers, etc.)
  • Misconfigurations (default settings, open shares, weak ACLs)
  • Known software vulnerabilities (scan against CVE databases)
  • Weak SNMP configurations (default community strings, excessive permissions)

• Active Directory Vulnerabilities:

  • Weak/default passwords
  • Kerberos weaknesses (roasting, golden/silver tickets)
  • Unconstrained delegation
  • Excessive permissions and overprivileged accounts
  • Trust vulnerabilities (forest/domain trusts)

• Peripheral Vulnerabilities:

  • Default credentials (device web interfaces)
  • Outdated firmware and known exploits
  • Configuration weaknesses (open file shares, insecure protocols)

Phase 4: ExploitatioPrioritise

Focus on vulnerabilities with high potential impact (privilege escalation, domain compromise, sensitive data exfiltration)

• Network Devices: Target weak passwords, configuration flaws, and known exploits (e.g., router vulnerabilities) to gain control or disrupt network traffic.
• Active Directory: Exploit weak passwords, Kerberos attacks, delegation issues, etc., to elevate privileges and gain domain-wide access.
• Peripherals: Attempt unauthorised, exfiltrate print jobs, intercept network traffic, and use as pivot points for further attacks.

Phase 5: Reporting

• Technical Report: Detail vulnerabilities, exploit paths, evidence, attack impact, CVSS scores, and step-by-step remediation guidance.
• Executive Summary: Non-technical explanation of risks, potential business impact, and high-level mitigation strategies.

Phase 6: Post-Test

• Remediation Support: Collaborate with IT teams on fixing vulnerabilities, hardening AD, and securing devices.
• Lessons Learned: Review the test to refine the process and improve future internal penetration testing assessments.

Important Considerations

• Test plan: At Cyphere, we ensure all customers know the prerequisites, scheduling, resourcing and engagement specifics through a detailed test plan. It allows multiple parties (where involved) and relevant stakeholders to follow a mutually agreed-upon reed approach and ensure smoother execution of the internal pentest.
• Staging Environment: Test risky exploits in a lab first to avoid disruption in a customer’s production environment that can have huge effects on the operational side.
• Communication: Maintain open communication with stakeholders before, during, and after the test. This is one of the differentiating factors of service quality-based security consultancies from point-and-click scanning work.

Internal network penetration test tools and utilities

Internal penetration testers have specialised toolkits for specialised-world attackers operating within your network. Let’s dive into some key categories:

Nmap

The king of network mappers, Nmap helps identify live hosts, open ports, running services, and operating system details – a vital foundation for any internal test.

Arp-scan

Uncovers MAC addresses and devices on your local network segment, often revealing hidden systems.

Nessus

It is a popular commercial option with vast vulnerability coverage and excellent reporting features.

OpenVAS

A powerful open-source alternative to Nessus, offering deep vulnerability scanning capabilities.

Metasploit Framework

The industry standard for exploit development and execution. It offers a massive library of exploits and payloads, streamlining the process of weaponising discovered weaponising ties.

Password tools

Password tools such as CeWL, Hashcat, and John the Ripper for password cracking.

Exfiltration tools

Exfiltration tools such as Iodine, Client/server C2 tools (TrevorC2), dnscat.

PowerShell tools and utilities

Pen testers are famous for helping in-house utilities gain access to the target systems. Built into Windows, PowerShell is versatile for reconnaissance, automation, and post-exploitation tasks.

Custom scripts

Pen testers often develop scripts in Python or Bash to automate everyday tasks or execute unique attack vectors.

Internal Infrastructure Penetration Testing Methodology

An internal penetration testing methodology provides a structured and systematic approach to evaluating the security posture of an organisation’s internal organisation. These methodologies guide pen testers in identifying vulnerabilities, exploiting them safely, documenting attack paths, and providing a roadmap for security improvements.

Using these methodologies sets an excellent benchmark for customers to ensure test cases are covered thoroughly against their environment.

Common Internal Penetration Testing Methodologies

• PTES (Penetration Testing Execution Standard): Offers detailed technical guidelines for penetration testing, divided into seven main phases. PTES includes steps relevant to planning, conducting, and reporting on internal pentests.
• NIST SP 800-115 (Technical Guide to Information Security Testing and Assessment): A NIST (National Institute of Standards and Technology) publication providing broad guidance on security testing. It includes sections applicable to internal infrastructure penetration, planning, discovery, and reporting.
• OSSTMM (Open Source Security Testing Methodology Manual): A comprehensive framework emphasising scientific emphasising goes beyond traditional network penetration testing to address physical security, wireless, human (social engineering), and operational processes.

When to perform internal penetration testing?

• After major changes: When significant network infrastructure changes occur, roll out new applications or major system updates. These introduce potential new vulnerabilities.
• Annually or regularly: Internal penetration tests should be part of your ongoing security program. Annual or even semi-annual testing is ideal. More frequent testing may be needed for high-risk environments or those subject to strict compliance standards. For instance, many organisations are now upgrading their workstations and servers or making other significant changes that necessitate the internal pen test to validate new security controls and any gaps that could pose a risk to the organisation.
• CompliancorganisationIf you operate in a regulated industry (healthcare, finance, etc.), compliance frameworks like PCI DSS and NHS DSPT (Data security protection toolkit) may mandate specific pen testing frequencies.

How long does internal penetration testing take?

Most internal pen tests for small- to medium-sized organisations take up organisations. Large organisations take a long time to deal with complexors such as multiple domains, internal networks, workstations, servers, and segmentation zones.

• No simple answer: The duration depends heavily on your network’s size and coScopeity, the test’s Scope, and the Scoper of systems in Scope.
• Estimate: A small to medium internal network might be tested within a week or two. Larger, more complex environments could take several weeks.
• Phased Approach: For pervasive environments, breaking the testing into phases targeting specific network segments is sometimes more practical.

Internal penetration test checklist to follow

A robust checklist is detailed, but here’s a high-level structure to ensure you address the core elements:

1. PScopegagement

• Define Scope (assets, objectives, off-limits systems)
• Rules of Engagement
• Secure tester access/accounts

2. Reconnaissance

• Network Mapping
• Active Directory Mapping (if relevant)
• User Enumeration

3. Vulnerability Identification

• Automated ScansPrioritiseze manual validation)
• Service version checks
• Any low-hanging fruits such as null session RID cycling, default credentials, open files, shares
• Configuration reviews (if applicable)

4. Exploitation

• Prioritise by potential impact
• Attempt privilege escalation
• Lateral movement simulation

5. Reporting

• Technical report (vulnerabilities, evidence, reproduction steps)
• Risk assessment (criticality, likelihoodPrioritiseded remediation recommendations
• Executive summary for non-technical stakeholders

6. Post-Test Debrief

• Walkthrough with IT team and stakeholders
• Remediation support & guidance

How Cyphere can help?

Cyphere provides CREST-accredited internal penetration testing services to uncover security flaws within your network before attackers can exploit them. Our tailored assessments help you prioritize risks and deprioritised remediation strategies to strengthen your security posture.

Know your unknowns through internal pentest to assess and quantify the internal network security vulnerabilities and prepare a risk mitigation approach to reduce the attack surface and improve internal security posture – the most critical component of a corporate cyber security strategy.

Frequently Asked Questions

What are internal and external pen testing?

• Internal penetration testing simulates an attack from within your network, focusing on vulnerabilities accessible to employees or those who have already breached your perimeter.
• External penetration tests target your internet-facing systems and identify vulnerabilities an attacker could exploit from the outside. An external pen test is based on black box test methodology.

Which team conducts internal penetration testing?

Internal penetration testing is conducted by ethical hackers hired from security consultancies such as Cyphere, NCC Group, Trustwave or others. Ethical hacking simulates insider threat scenarios or other test cases that are tailored to the organisation’s needs.

How do you perform internal penetration testing?

Ideally, internal pentest should be conducted at least annually or more frequently in high-risk environments or after significant network changes.

Which internal data are prone to security vulnerabilities?

Sensitive data like customer information, financial records, intellectual property, and healthcare data are desirable targets and, therefore, most at risk.