An external network penetration test (pentest) assesses your digital perimeter’s resilience to attacks such as phishing, brute-force password attacks, and SQL injection. This gives you insights into vulnerabilities that might be used by attackers who haven’t yet penetrated your perimeter. Conducting external network pentests helps you protect critical assets by securing your security perimeter before attackers get an initial foothold.
Along with internal pentesting, external pentesting forms a vital part of an effective offensive security strategy. In this guide, we’ll cover what it is, what it’s for, how it works, and why you need it.
An external network penetration test is a simulated cyberattack targeting an organization’s internet-facing perimeter. It attacks vulnerabilities exposed through publicly available information as well as public-facing network components such as IP addresses, networking devices, open ports, webcams, printers, and IoT devices. This reveals what an attacker can discover and exploit when they’re outside your network looking in.
External network pentests expose vulnerabilities such as leaked credentials, open ports, unsecured network devices, unpatched software, and insecure plain-text pastebins. Attackers who can exploit these vulnerabilities can achieve objectives such as stealing customer data, hijacking email servers to send spam, altering websites, or disrupting service.
Pentesters conduct external network tests using tools such as network scanners, directory and file enumeration tools, search engine crawlers, attack surface management (ASM) platforms, vulnerability scanners, and HTTP proxies. These tools, along with others, help pentesters create a comprehensive map of your network to manually probe vulnerabilities.
After identifying vulnerabilities, pentesters prioritize them by severity and provide reports recommending remediations. After recommended fixes have been applied, retesting is performed to verify that remediation is completed completely. This ensures development teams are empowered to remediate complex vulnerabilities such as chained exploits.
External network pentests aim to achieve a number of objectives:
Not all of these goals are necessarily included in every pentest. Customized tests may focus on specific areas. Likewise, not all goals are pursued at once, but in successive phases of the pentesting process.
External pentesting is not limited to networks. Security teams also apply external pentesting methods to other external-facing attack surfaces, including:
Whether any of these additional methods apply to your security needs depends on the nature of your attack surface and your priorities.
External pentesting works in tandem with internal pentesting. Where external pentests focus on initial entry through the front door of network perimeters, internal pentests hone in on intruder activity after a breach has occurred.
Once an attacker is inside your network, they may pursue actions such as:
Running internal pentests helps protect you against these follow-up stages of attack that occur after external penetration. Both external and internal pentests are needed for comprehensive coverage of your network’s vulnerabilities.
Defining the scope of your attack surface forms a vital prerequisite for performing external network pentests. Typical components of external network attack surfaces include:
The exact components of your network that need to be tested depend on the breadth of your organization's digital footprint.
The external network pentesting process can be broken down into four phases:
Here’s a more detailed breakdown of what each phase involves:
The reconnaissance phase begins with a search for publicly available information that attackers can gather from outside your network without internal access. This provides testers with insight into which resources hackers might use to gain initial access to your network.
To conduct reconnaissance, pentesters investigate sources such as:
Pentesters conducting reconnaissance are assisted by tools such as Nmap, DirBuster, Shodan, and Censys. These tools help identify targets on your network perimeter, such as IP addresses, routers, firewalls, open ports, and other Internet of Things devices
By gathering this information, pentesters can identify vulnerabilities such as Exposed user data and files, open ports, insecure devices, outdated software, or exposed assets
The initial information gathered during reconnaissance provides pentesters with a basis for probing your attack surface to identify potential attack vectors.
In the next phase of the pentesting process, testers use the information gathered during reconnaissance to scan your ports and active services and discover vulnerabilities. Port scanning yields initial information that can be used to deepen knowledge of your network. Scans are conducted using tools such as:
Running complete port scans across IP address ranges for your assets reveals signatures of public-facing machines and active services running on your network. These detectable signatures may indicate:
Scanning for this information provides data that can be used to collect additional information on your network, such as:
The scanning process may discover active services without associated functions, which can indicate misconfigurations, inactive identities, or missing API permissions.
Pentesters follow up port-scanning analysis with vulnerability scanning to discover ways attackers might exploit identified machines, active services, and software to gain internal access to local area networks and resources. To analyze this, pentesters use tools such as:
Vulnerability scanning yields the information pentesters need to identify attack vectors hackers are likely to use.
The next phase enters the heart of the pentesting process, as testers manually attempt to exploit vulnerabilities that have been identified in the previous phase. Pentesters usually focus on visibly open surfaces. For example, a typical process involves attempting to exploit vulnerabilities in DNS servers, routers, firewalls, and other systems.
Attempting to exploit these attack surfaces may involve actions such as:
Depending on network specifics, additional custom tests may be performed. During the exploitation phase, pentesters avoid executing exploits that could disrupt services or affect customers. Instead, in these cases, testers limit their activity to noting potential risks.
At the conclusion of the pentesting process, testers produce reports summarizing their findings and recommending fixes. Findings can be divided into current findings from the ongoing test and historical findings that provide context from previous tests.
To assist with applying testing results, findings can be filtered and sorted according to select criteria, searched by keyword, or exported in CSV format for local analysis or external reporting. Current findings can be filtered by criteria such as:
Historical findings reports classify previously found vulnerabilities by grouping them based on whether:
In addition to reporting on vulnerabilities, pentesters recommend remediations and provide guidance on implementing fixes. Findings can be remediated during ongoing pentests or after pentests have been completed. After remediation attempts, retesting can be done to ensure that fixes have been successful.
By tracking historical data and testing remediations, pentesting becomes an ongoing, iterative process of continuous improvement. This helps ensure that your security posture keeps pace with the current threat environment and regulatory requirements.
External network pentesting has become a necessity for organizations for a variety of reasons, ranging from security and business needs to regulatory compliance requirements.
The ever-growing proliferation of network devices in today’s cloud-based, IoT-connected environment has expanded the external attack surface, while AI has accelerated attack frequency and the adaptation of attack methods. Leaving your external network untested exposes your organization to risks like data theft, ransomware attacks, email server hijacking, service disruption, or website defacement.
Risk management represents another driver of external network pentesting. As news reports of major data breaches and financial losses have become commonplace, boards and stakeholders are investing in cybersecurity as a risk-mitigation strategy, with pentesting as a cornerstone of security risk management.
Tightening regulatory requirements are likewise increasing the urgency of external network pentesting. Some industry frameworks, like Payment Card Industry Data Security Standard (PCI DSS), mandate pentesting, while others recommend pentesting as the most efficient way to meet regulatory obligations.
Together, these factors combine to create a need for third-party validation of security posture. Verifying the security of your network and the effectiveness of your security policies is a sound business strategy and, increasingly, a legal obligation to do business.
External network pentesting forms one prong of a complete offensive cybersecurity strategy. A complete strategy includes external pentesting, internal pentesting, and other methods such as red teaming.
To learn more about offensive security and other cybersecurity topics, visit the Cobalt Offensive Security Learning Center.