As organisations adapt to hybrid working models and more complex IT ecosystems, the historic notion of perimeter defence has all but dissolved. Today, some of the most significant threats come from within the network, and internal penetration testing is fast becoming a vital tool in identifying them.
Insider threats, whether malicious or accidental, pose a growing risk. Misconfigured user access, unpatched legacy systems, unmanaged endpoints, and unsecured collaboration tools can all create vulnerabilities that attackers exploit once inside the network. In hybrid work environments, where employees routinely connect via personal devices, home Wi-Fi, and cloud platforms, the traditional assumptions of internal network trust no longer apply.
That’s why security leaders are increasingly adopting internal penetration testing: a proactive approach to identifying weaknesses behind the firewall before they’re exploited. Unlike external pen tests, which simulate attacks from outside the organisation, internal tests simulate what could happen if an attacker (or compromised user) gains access to the internal environment.
These tests explore lateral movement, privilege escalation, data exfiltration paths, and shadow IT risks. For example, can an attacker pivot from a printer to a file server? Can they access HR records from a misconfigured endpoint? Can a junior staff member escalate permissions due to overly broad group policies?
Threat modelling has evolved to reflect this shift. Security teams are moving beyond edge-case scenarios and focusing on realistic, business-specific risks, such as disgruntled employees, compromised contractor accounts, or an attacker exploiting a legacy intranet tool no longer supported by IT.
Importantly, internal pen testing also supports broader governance and compliance needs. Frameworks like ISO 27001, Cyber Essentials Plus, and NIS2 now place increasing emphasis on internal controls, privilege management, and incident response readiness. Pen tests help validate that these controls work not just on paper, but in real-world scenarios.
Hybrid working further complicates the picture. Remote endpoints, often outside the protection of on-prem firewalls, introduce new risks. Internal pen tests can simulate compromised laptops connecting to corporate VPNs or misconfigured cloud storage accessible to non-corporate devices.
Ultimately, internal pen testing is is about recognising that in a hyper-connected, hybrid world, the lines between external and internal threats are increasingly blurred. By expanding testing beyond the perimeter, cybersecurity leaders can gain a realistic view of their risk exposure and build defences where they’re needed most: on the inside.
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