External vs Internal Network Penetration Testing

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Strong network security is a fundamental responsibility for all organisations and businesses. Weak cybersecurity can be extremely damaging to your company with severe brand and financial implications.

External and internal network penetration testing is the solution to security testing and leads to remedial actions. Pen tests are carried out by security companies with ethical hackers that have extensive knowledge of offensive security.

The penetration tests check for vulnerabilities of an organisation’s network, computers, laptops, software, wired and wireless systems, applications, cloud networks, email servers, routers, and employees. The scope of the test is agreed upon and includes internal and external testing.

 External pen tests asses your organisation’s perimeter defences, while internal tests assess weaknesses once your network has been compromised. The analysis uses automated and manual tools to test different attack paths. 

 In some industries, penetration testing is mandated, such as government departments, healthcare, and financial services. For other organisations, testing should take place at least once or twice a year.

Here we take a look at external vs internal network penetration testing.

External network penetration testing 

External network penetration testing looks to exploit weaknesses from an external position, with no pre-permissions or access. This simulates an attack by a cybercriminal, looking to compromise or steal a company’s information.

By simulating an external cyberattack, your company will find out if its existing security measures are adequate. 

External penetration tests include:

  • Authorisation testing
  • Authentication testing
  • Cryptography testing
  • Business logic testing
  • Identity Management testing
  • Client-side testing
  • Session management testing
  • Input validation testing
  • Error handling testing

Internal network penetration testing 

Internal network penetration testing is one level above vulnerability scanning and typically takes place after external penetration testing. Internal pen tests attempt to exploit detected internal weakness to reveal what data is at risk and the potential impact this could pose.

The simulated cyberattack comes from a cybercriminal who has gained access to the company’s internal network. The testing is also conducted from an attack by an on-site contractor or employee.

Internal penetration tests assess network elements such as access points, computer systems, firewalls, Wi-Fi networks, employees, and local servers, as well as IDS/IPS. They also assess the effects of malware spreading, privilege escalation, and other malicious activities.

Internal penetration tests include:

  • Firewall and ACL testing
  • Internal network scanning
  • Database control testing
  • Password strength testing
  • Social engineering testing
  • Port scanning
  • System fingerprinting
  • Trojan scanning
  • Manual vulnerability testing
  • Networked equipment control testing
  • Vendor/third-party configuration testing

Pen test reporting

Once internal and external penetration testing is completed, your company receives a debrief and a formal written report of the findings. This report highlights detected software flaws, insecure or non-configured firewalls, inadequate security controls, malware presence, and unpatched systems.

The pen test report also highlights what remedial action should be taken to address the risks. This list of steps is prioritised by the level of risk and potential impact on your organisation.

Businesses need to perform both external and then internal penetration tests to determine the effectiveness of technical security controls and policies. It is necessary to conduct regular security audits to tackle the fast pace of developing cyberattack techniques, the weaknesses that become known in software and hardware and to conform with security regulations.

To ensure penetration testing is carried out successfully, you should choose a third-party cybersecurity company that is CREST accredited and uses Certified Infrastructure Testers (CCT INF).

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