External VS Internal Network Penetration Tests

External VS Internal Network Penetration Tests: What’s The Difference?

Penetration testing, also known as ethical hacking, is the practice of checking the security weaknesses of an application software, computer system or network. Penetration tests can be either external or internal depending on the goal of the project.


An external penetration test researches and attempts to exploit vulnerabilities that could be performed by an external user without proper access and permissions. An internal penetration test is similar to a vulnerability assessment, however, it takes a scan one step further by attempting to exploit the vulnerabilities and determine what information is actually exposed.


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What Are The Benefits Of Penetration Tests?


Because cyber security is a day to day effort, penetration testing has evolved to become an integral part of most comprehensive security programs. The goal of a penetration test is to identify security vulnerabilities which could be exploited by an attacker.



A licensed penetration tester performs a cyber attack on an organization’s IT assets either remotely or physically to simulate a real attack. A penetration test determines whether unauthorized access or any malicious act is possible.


The report provided by a penetration test can be used to strengthen an organization’s security policy and adherence of compliance requirements.


Performing penetration tests regularly help to:


  • Determine weakness in the hardware, software, or human assets of an organization in order to develop controls.
  • Maintain the 3 triads of cyber security – Confidentiality, Integrity, and Availability.
  • Ensures that controls which have been implemented are adequate.
  • Provides intelligence and insight of an organization’s security measures by understanding how it could be and likely will be attacked and what steps should be taken to secure the organization.
  • Improve the overall security posture of an organization.


It’s typically best practice for businesses to perform penetration tests at least 1 – 2 times per year, however, compliance requirements or major infrastructure changes may require more frequent tests.


What Is An External Penetration Test?


External penetration testing consists of testing vulnerabilities to review the chances of being attacked by any remote attacker. By exploiting the found vulnerabilities it identifies the information being exposed to outsiders.


The main objective of this test is to simulate an attack on the internal network by mimicking the actions of an actual threat actor.


This type of penetration testing attempts to find and exploit vulnerabilities of a system to steal or compromise the organization’s information. As a result, the test will show whether the implemented security measures are enough to secure an organization and to assess its capability to defend against any external attack.


On average, an external penetration test will take 2-3 weeks to complete. However, this depends on the complexity of the system, the size of the network, and the goals of the test itself.


Examples of external penetration tests include:


  • Configuration & Deployment Management Testing
  • Identity Management Testing
  • Authentication Testing
  • Authorization Testing
  • Session Management Testing, Input Validation Testing
  • Testing for weak Cryptography
  • Business Logic Testing
  • Client Side Testing
  • Testing for Error Handling.


External penetration testing methodologies include:


  • Footprinting
  • Checking for public information and other information leakages.
  • System Scanning/Port Scanning/Service Scanning for vulnerabilities
  • Manual testing identified vulnerabilities.
  • IDS/IPS Testing
  • Password Strength Testing


Popular tools used in external penetration tests are:


    • Nessus
    • Metasploit
  • Burp Suite Pro
  • Dirbuster/Dirb/GoBuster
  • Nikto
  • Sqlmap
  • Recon-ng
  • Nmap
  • Hydra
  • GHDB
  • theHarvester


What Is An Internal Penetration Test?


An internal penetration test uses a different way of dealing with the attacks and comes into the picture after completion of an external penetration test. In this test, the main focus is to identify what could be accomplished by an attacker who has internal access to your network.


This can be a threat actor who penetrated the organization’s external defense systems or it can be an employee, contractor, or other staff with internal access.


Internal penetration tests include using:


  • Computer Systems
  • Access Points
  • Wi-Fi Networks
  • Firewalls
  • Local Servers
  • Employees


Once those vulnerabilities are identified, testers exploit them to discover the impact of an attack and show the weakness/entry points to the organization.


Internal penetration testing is not just limited to exploiting internal network vulnerabilities, but it also includes privilege escalation, malware spreading, man in the middle attacks (MITM), credential stealing, monitoring, information leakage or any other malicious activity.


You might be wondering why you would conduct an internal penetration test, to begin with, given your systems are supposedly secure from any external threats.


However, internal tests provide the results to an organization that should an attacker manage to gain access equivalent to an insider, or if any malicious internal user tries to break the security, what impactful it could have in terms of disclosure, misuse, alteration, or destruction of organization’s confidential information.


Internal penetration testing methodologies include:


  • Internal Network Scanning
  • Port Scanning and System Fingerprinting
  • Finding vulnerabilities
  • Exploiting
  • Manual Vulnerability Testing and Verification
  • Firewall and ACL Testing
  • Administrator Privileges Escalation Testing
  • Password Strength Testing
  • Network Equipment Security Controls Testing
  • Database Security Controls Testing
  • Internal Network Scan for Known Trojans
  • Third-Party/Vendor Security Configuration Testing


Popular tools used in internal penetration testing:


  • Nmap
  • Wireshark
  • Burp Suite Pro
  • Dirbuster/Dirb/GoBuster
  • Nikto
  • Sqlmap
  • Nessus
  • Responder
  • Metasploit Framework
  • Nmap
  • Hydra
  • Bettercap/Ettercap
  • Hashcat/John the Ripper
  • Custom Scripts




For every organization, best practice is to perform an external and internal penetration test along with regular security audits to ensure security of their IT System and determine what information can be exposed to the attackers. It is also necessary because of IT Security Rules & Regulations and Guidelines like GLBA, FFIEC, NCUA, HIPAA, and etc.


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Jason Firch

Jason is a veteran IT operations manager, digital marketer, as well as the co-founder and CEO of PurpleSec, with nearly a decade of experience in business management and operations. When he's not studying for his CISSP or contributing to the PurpleSec blog you'll find Jason helping nonprofits with their online marketing.

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