Most companies spend a lot of time trying to keep cyber attackers out. Firewalls, antivirus, and multi-factor authentication are all about protecting the perimeter.
But what if someone’s already inside?
Maybe it’s a stolen password. Maybe it’s an employee who clicked the wrong link. Either way, once that barrier is crossed, the real question becomes: how far could an attacker get before you even notice?
That’s why penetration testing matters, not just to simulate outside attacks, but also to see what happens after someone’s in.
Penetration testing is a way to safely test your defences by simulating real-world attacks. There are two main types: external, which mimics threats from the internet, and internal, which assumes the attacker already has a foothold.
In this guide, we’ll walk through the key differences between internal and external penetration testing, when to use each, and why both are important to strengthening your overall security measures.
What Is Internal Penetration Testing?
Internal network penetration testing simulates attacks that originate from within an organisation’s network perimeter. This type of penetration testing assumes that an attacker has already gained some level of access to the internal network, either through compromised employee credentials, physical access to the premises, or by successfully breaching external defences.
During internal pen testing, security professionals operate from within the organisation’s network infrastructure, typically connecting directly to internal network segments. This positioning allows them to assess security controls from an insider’s perspective, evaluating how well the organisation can detect and respond to threats that have bypassed perimeter defences.
Concerned that your internal defences might not stand up to a motivated attacker or a disgruntled insider? Contact our team to perform a targeted internal penetration test and protect your organisation from within.
What Is External Penetration Testing?
External network penetration testing evaluates an organisation’s security posture from an outsider’s perspective, simulating attacks that originate from the internet or other external networks. This testing approach mirrors the initial stages of most real-world cyberattacks, where malicious actors attempt to breach an organisation’s perimeter defences to gain their first foothold in the target environment.
External pen testing operates from outside the organisation’s network, using only publicly available information and the same tools and techniques that real attackers would employ. This approach provides an authentic assessment of how well an organisation’s external-facing assets can withstand attack attempts from external threats and motivated adversaries.
Internal vs External Penetration Testing: What are the Key Differences
Understanding the fundamental differences between internal and external penetration testing is essential for developing a security testing strategy:
| Aspect | External Penetration Testing | Internal Penetration Testing |
|---|---|---|
| Attack Perspective | Begins from outside the network with no prior knowledge or access, simulating real-world attack scenarios. | Starts from within the network perimeter, assuming initial compromise has already occurred. |
| Primary Target Systems | Internet-facing assets, web applications, email servers, VPN endpoints, DNS services, and publicly accessible infrastructure. | Internal network infrastructure, workstations, servers, Active Directory environments, databases, and internal applications. |
| Information Gathering | Relies on publicly available information through OSINT, reconnaissance, and external scanning. | Has access to internal network information, can observe internal communications, and system interactions. |
| Threat Actor Simulation | Simulates external attackers, cybercriminal groups, nation-state actors, and opportunistic hackers attempting initial compromise. | Simulates insider threats, compromised user accounts, lateral movement scenarios, and post-breach activities. |
| Testing Methodology | Extensive reconnaissance phase, limited exploitation time due to external monitoring, focus on initial access vectors. | Deeper exploitation and post-exploitation analysis, privilege escalation testing, and lateral movement assessment. |
| Network Access Level | No network access, initially, must gain access through exploitation of external vulnerabilities. | Already has network connectivity, focuses on exploiting internal trust relationships and configurations. |
| Detection Evasion | Must avoid external security monitoring, IDS/IPS systems, and perimeter controls. | Must evade internal monitoring systems, endpoint detection, and security operations centre (SOC) detection. |
| Compliance Focus | PCI DSS, external vulnerability requirements, and internet-facing system security standards. | Data protection regulations, privilege management requirements, and internal control validation frameworks. |
| Primary Deliverables | External attack surface analysis, perimeter security assessment, and web application vulnerabilities. | Network segmentation effectiveness, privilege escalation paths, internal data exposure risks. |
| Testing Duration | Typically, 1-3 weeks with an extensive planning phase. | Usually 2-4 weeks with a focus on thorough internal analysis. |
Benefits of Internal Penetration Testing
Internal penetration testing uncovers security risks inside your network, showing how attackers could move laterally, escalate privileges, and exploit security weaknesses and enhance detection.
- Identifies lateral movement vulnerabilities – Reveals how attackers can expand access once they’ve gained an initial foothold.
- Shows speed of internal compromise – Demonstrates how quickly and extensively attackers could move through internal systems.
- Validates network segmentation strategies – Ensures systems are properly isolated from general user networks.
- Provides Active Directory security insights – Identifies misconfigurations, excessive privileges, and vulnerable trust relationships.
- Enables privilege escalation detection – Reveals pathways that could allow attackers to gain administrative access.
- Evaluates internal monitoring capabilities – Tests whether SOC teams can detect and respond to threats that bypass perimeter defences.
- Improves incident response procedures – Provides feedback essential for enhancing security tool effectiveness.
- Validates insider threat controls – Assesses protection against malicious employees or compromised internal accounts.
- Ensures compliance requirements – Meets internal control validation mandates for various regulatory frameworks.
If your business is serious about security, penetration testing isn’t optional. Reach out to us today to discuss your goals, systems, and compliance requirements, and we’ll help you determine the most effective testing plan.
What Does Internal Penetration Testing Cover?
Internal penetration testing examines areas within your network to identify weaknesses that could be exploited by attackers with insider access. It focuses on uncovering unauthorised access, privilege escalation paths, and vulnerabilities that could put sensitive data and systems at risk.
- Access to sensitive files and systems inside the network – Testing unauthorised access to confidential databases, file servers, and important applications
- Privilege escalation (gaining higher access rights) – Attempting to gain administrative or root privileges from standard user accounts
- Lateral movement (moving across different network segments) – Testing the ability to move between network zones and access restricted areas
- Exploitation of internal services and misconfigurations – Identifying vulnerable internal applications, services, and system configurations
- Weaknesses in internal user authentication and access controls – Evaluating password policies, multi-factor authentication, and user permission structures
When Should You Choose An Internal Penetration Test?
Choose internal penetration testing for the following situations:
- After suspected or confirmed security incidents – Understanding the potential compromise scope and identifying additional vulnerabilities
- Managing complex internal networks – Multiple network segments or sophisticated Active Directory environments require regular assessment
- Experiencing insider threat concerns – High employee turnover or disgruntled employee situations warrant internal testing
- Storing sensitive data internally – Organisations with internal databases and file systems need validation
- Operating infrastructure – Systems requiring additional protection layers benefit from an internal assessment
- Implementing zero-trust architecture – Validating micro-segmentation and identity-based access controls
Benefits of External Penetration Testing
External penetration testing helps organisations understand how vulnerable their public-facing systems are to real-world cyberattacks. It uncovers weaknesses in the perimeter defences, validates security assets, and protects necessary customer-facing services from potential breaches.
- Simulates real-world attack scenarios – Provides authentic insights into how actual attackers approach target organisations
- Reveals external vulnerability exposure – Shows genuine attack likelihood from internet-based threats
- Reduces unnecessary exposure – Helps organisations minimise their external footprint and implement appropriate perimeter controls
- Validates perimeter security investments – Ensures firewalls, intrusion detection systems, and web application firewalls provide expected protection
- Confirms security tool effectiveness – Verifies that significant security investments are working as designed
- Assesses web application security – Identifies vulnerabilities in customer-facing applications and partner portals
- Protects customer trust – Critical for maintaining confidence in public-facing services and applications
- Prevents data breaches – Helps identify and fix vulnerabilities before malicious actors discover them
- Ensures regulatory compliance – Meets external security testing requirements for various industry standards
Think your internal systems are secure from insider threats, privilege escalation, or lateral movement? Contact us today and let our experts simulate a real-world breach scenario within your network to uncover what’s really at risk.
What Does External Penetration Testing Cover?
External penetration testing focuses on identifying vulnerabilities in your publicly accessible systems, including servers, firewalls, exposed services, and authentication portals. It may also assess your organisation’s susceptibility to social engineering or phishing attacks.
- Internet-facing servers and applications (websites, email servers, VPNs) – Testing all publicly accessible systems for vulnerabilities
- Network firewalls and perimeter defences – Evaluating the effectiveness of boundary security controls
- Publicly exposed ports and services – Identifying unnecessary services and potential entry points
- Vulnerabilities in authentication systems accessible externally – Testing remote access portals, VPNs, and web-based login systems
- Social engineering or phishing susceptibility (sometimes) – Assessing human vulnerability to targeted attacks
When Should You Choose An External Penetration Test?
Choose external penetration testing for the following situations:
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- Launching new internet-facing applications or services – These represent new potential attack vectors requiring validation
- Operating a significant web presence – E-commerce operations or customer-facing digital services need regular external testing
- Undergoing digital transformation initiatives – Changes that increase internet footprint or alter external attack surface
- Meeting regulatory compliance requirements – Particularly for financial services, healthcare, and retail industries
- Experiencing frequent external attack attempts – Organisations under constant threat need regular perimeter validation
- Implementing new cloud services – Cloud migrations and new SaaS integrations require an external security assessment
Final Thoughts!
Understanding the differences between external and internal penetration testing empowers your organisation to tailor security efforts effectively. Whether guarding against external hackers or insider threats, both forms of pen testing are critical in building cyber defences.
If you’re looking to safeguard your business and want expert assistance with penetration testing tailored to your needs, reach out to a trusted cybersecurity partner today. The right tests today can prevent tomorrow’s costly cyber disasters. Contact us to schedule a no-obligation consultation and learn how our penetration testing services can expose real risks before attackers do.
