External Network Penetration Testing Best Practices

With the growing number of websites and digital services, companies face a higher risk of cyber threats. Institutions such as financial firms, governmental agencies and e-commerce platforms must rigorously test their security to protect customers from fraud and maintain their trust. A single breach can result in significant financial losses and irreparably damage a company’s reputation. Identifying security weaknesses and implementing security controls is necessary for every company, which is why external network penetration testing is in high demand.

At EPAM, we specialize in performing this type of testing. Below, we share our expertise, covering how we execute external network penetration tests, the key elements we target, the techniques we use and how we address security vulnerabilities.

What is External Network Penetration Testing?

External network penetration testing simulates real-world attacks from outside your network to identify vulnerabilities and security issues in internet-facing assets like websites, email servers and external services.

This process benefits businesses by reducing the risks of compliance violations, reputational loss and legal issues. Reputation is crucial; it helps retain customers based on trust and high-level security. It ensures users experience a secure and reliable digital environment where sensitive data is protected.

When Is It Needed?

External network penetration testing is particularly necessary during the following events:

• Before Launching New Services or Applications: To ensure security and prevent vulnerabilities.

• After Network Changes: To verify that updates to software, hardware or configurations haven’t introduced new threats.

• During Security Audits: To assess an organization’s security posture against evolving threats.

• To Meet Compliance Standards: To adhere to regulations, protect sensitive data and avoid penalties.

• After Security Breaches: To identify existing vulnerabilities and prevent future incidents.

• When Adopting Cloud Services: To secure cloud configurations and internet-exposed services.

• As Part of a Risk Assessment: To proactively identify and mitigate potential threats.

External vs Internal Penetration Testing

External penetration testing targets vulnerabilities accessible from outside an organization’s network, while internal testing focuses on weaknesses within. Both are critical, but they address different threats.

So, we have explored how these two types of penetration testing differ. Now, let's proceed to discuss the network elements that are commonly targeted by malicious attackers.

Commonly Tested Network Elements

External penetration testing in network security involves examining specific areas of the network that are accessible or affected from outside. At EPAM, external penetration testing evaluates specific internet-facing areas:

• Web Applications: These include all the public-facing web applications that can interact with users outside the organization, such as e-commerce sites, login portals, and informational websites. High-level testing typically focuses on the most prominent features and functionalities exposed to the internet rather than delving deep into the application layers, which is time-consuming.

• Network Services: This includes testing all your network's external services, such as FTP, SSH and VPN services. The goal is to evaluate the security controls to protect these services from unauthorized access and ensure they are properly segregated from the internal network.

• Email Systems: Penetration testers evaluate email systems focusing on external configuration audits, potential information leakages such as email enumeration and thorough authentication and authorization checks.

• Firewalls and Routers: This includes determining if malicious data can pass through undetected and assessing unauthorized network access vulnerabilities. Additionally, testers evaluate the configurations and software versions of these systems, particularly firewall management systems, to identify any vulnerabilities that have been commonly exploited in recent incidents.

• DNS Servers: Penetration testing on these servers focuses on identifying vulnerabilities that could lead to DNS spoofing or hijacking, potentially rerouting users to malicious sites. Pen testers also assess for sensitive information leakage due to improperly configured DNS servers or revealing DNS records. These server evaluations help prevent unauthorized access to internal information that might contain sensitive data.

• API Endpoints: External APIs that allow other applications to interact with your system are assessed generally to ensure they reject unauthorized requests and prevent data leaks or breaches.

Testing Techniques

To identify vulnerabilities, various testing techniques are used:

• Port Scanning: This technique involves scanning the network's external IPs to identify open ports. The results can show what services are exposed to the internet and whether any should be restricted or better secured.

• Vulnerability Scanning: A semi-automated approach, which includes various automated tools and manual techniques to identify vulnerabilities in the system, such as outdated software versions, misconfigurations and weak default settings.

• Brute Force Testing: This test attempts to gain access to systems by trying numerous password combinations to bypass authentication. It helps organizations understand the strength of their password policies and the effectiveness of account lockout mechanisms.

• Exploit Testing: After vulnerabilities are identified, penetration testing involves attempting to penetrate these weaknesses to understand the actual level of risk and impact they could have on the organization. This helps prioritize which vulnerabilities should be addressed first based on their exploitability and potential damage.

Common Attack Vectors in External Network Penetration Tests

External penetration tests often identify these attack methods:

• Exploitation of Web Application Vulnerabilities: Vulnerabilities include cross-site scripting (XSS), SQL injection, cross-site request forgery (CSRF), broken access control, insecure design and vulnerable and outdated software. They can be used to change online apps, preventing permitted access to private information or interfering with the operation of the application. These security flaws are frequently used by real-world attackers to obtain more thorough access to the data and systems underneath.

• Misconfigurations and Unpatched Software: Exploiting poor-quality or default software and system configurations including outdated software improperly set access restrictions and open ports that shouldn't be accessible.

• Credential Theft: Stealing login credentials remains a favored strategy for real-world attackers with easy access to systems and data. Techniques like phishing, spear-phishing or using credentials obtained from third-party breaches are common. Attackers can then pose as legitimate users, bypassing access controls and gaining unrestricted access to sensitive systems and data.

• Brute Force Attacks: A hacking method that cracks encryption keys, login credentials and passwords through trial and error of testing many combinations on a machine.

• Network Protocol Exploits: Exploitation of SSL/TLS or SMB vulnerabilities to intercept or manipulate traffic by attackers to perform tasks including denial-of-service attacks, session hijacking and man-in-the-middle attacks. For example, potential attackers can intercept or reroute traffic, steal data or interfere with network connections by taking advantage of flaws in SSL/TLS or the SMB (Server Message Block) protocol.

Penetration Testing Methodology

This section outlines the stages of conducting effective external penetration testing within networks. It can be effective external penetration testing within networks can be conducted by an internal security team if a company has its own well-equipped and experienced cybersecurity teams or, more commonly, by hiring external vendors. EPAM follows the Penetration Testing Execution Standard (PTES) in its process:

1. Pre-Engagement Interactions: Define test scope, goals, and legal considerations. Build the framework for the engagement and ensures both the penetration tester and the client understand the boundaries and objectives of the test.

2. Intelligence Gathering: This phase, also known as reconnaissance, is the collection of information like domain names, IP address ranges, network infrastructure details and publicly available information.

3. Threat Modeling: The penetration tester identifies and assesses potential vulnerabilities and threats on gathered data and targets.

4. Vulnerability Analysis: Identify weaknesses like outdated systems, misconfigurations and unpatched software vulnerabilities using automated tools and manual techniques.

5. Exploitation: A tester exploits identified vulnerabilities to gain unauthorized access or extract data, demonstrating the impact of the vulnerabilities and how they could be used by a malicious actor.

6. Post-Exploitation: Once access is gained, the penetration tester may explore the network to discover more about its structure and the data. An assessment identifies what’s possible after the attacker’s breach like escalating privileges, accessing sensitive data or establishing persistence on the network.

7. Reporting: Compiling all findings into a comprehensive report detailing vulnerabilities, exploitation methods, accessed data, and recommendations for remediation to improve the network’s security posture.

What Determines the Duration and Cost?

The duration and cost of penetration testing depend on network size, the number of IP addresses and test complexity.

Other factors include:

• Scope of IP address space

• Testing type (black box testing, gray box testing, etc.)

• Complexity of the network environment

Challenges in External Penetration Testing

Some common challenges include:

• Scope Management: A client is unsure which areas need testing or the depth of the defined scope, also known as scope creep, potentially impacting the effectiveness and focus of the penetration test.

• Legal and Compliance Issues: All stakeholders must be aware of testing activities to avoid perceived unauthorized access.

• Resource Constraints: Budget limitations often narrow the scope of testing, limiting coverage.

• Security System Detection and Blocking: Firewalls or IDS can block testing activities. Pre-authorization and clear communication are essential.

• Accurate Exploitation Without Disruption: During penetration testing, using public exploits can sometimes unintentionally disrupt systems or alter the condition of stored data.

• Dynamic and Complex Network Environments: Meticulous planning is essential for large-scale penetration tests involving dynamic and complex networks, such as those with 65,000 IPs or networks spread across various global locations and cloud providers. With a typical capacity for one engineer to handle up to 500 IPs, customers must coordinate with the provider well in advance to allocate the necessary number of skilled penetration testers.

• Post-Test Cleanup: Penetration testing can generate significant data in logs and may inadvertently modify existing data. Conducting thorough post-test cleanup is crucial to manage storage use and restore data integrity. Any sensitive information obtained from the customer during testing should be securely removed from the provider's systems.

External Network Penetration Testing Tools

Several tools are commonly used to uncover vulnerabilities:

• Nmap is a powerful network scanning tool used primarily for network discovery and security auditing. It’s most effective at quickly identifying devices running on a network, discovering open ports, and deducing what software and operating systems are in use.

• Nessus is a comprehensive vulnerability scanner that identifies network systems vulnerabilities, misconfigurations, and potential risks. Best applied in environments where maintaining high security across complex networks is essential, Nessus excels in thorough security assessments and regular security compliance checks.

• Hydra is a fast and flexible login cracker, performing rapid dictionary attacks against over fifty protocols, including FTP, HTTP and SSH. It is most effective in scenarios requiring testing the strength of passwords across various services.

• Patator is a universal brute-forcing tool that supports multiple protocols and services. Like Hydra but with extended capabilities across different services, Patator is effective in penetration testing tasks requiring the security of complex password systems and service configurations.

• Burp Suite is a comprehensive web vulnerability scanner that allows penetration testers to perform extensive security testing of web applications. It is ideally used in scenarios focused on web application security, offering tools to analyze, map and exploit web apps.

• Metasploit is a widely used framework for developing and executing exploit code against a remote target machine. Highly useful in conducting rigorous security checks, it allows testers to validate existing security controls against a database of known vulnerabilities and generic exploits.

• Nuclei is an automated vulnerability scanner designed for web and infrastructure testing based on templates. Perfect for continuous integration and continuous deployment (CI/CD) environments, Nuclei can quickly scan code, web applications and infrastructure for known vulnerability patterns before deployment.

• Agile Security Platform is a comprehensive suite of security tools and functionalities from EPAM designed to integrate with agile development processes. This platform is most effective when building security into the development lifecycle is critical.

EPAM’s Expertise

At EPAM, we offer Penetration Testing as a Service, providing organizations with rapid, advanced security audits. Our CREST accreditation demonstrates our commitment to security standards and best practices.