Firewall Penetration Testing: A Complete Guide

Just like you have locked doors and windows protecting your home or business, you should also have a solid firewall protecting your network and all the data you handle. Your firewall is a security perimeter that acts like a digital guard – deciding what traffic to let in based on the rules you set.

However, it’s easy to assume that just installing a firewall and leaving it to its own devices is enough from a security point of view. Sadly, with an increasing rise in cyberattacks each year, and with said attacks becoming more and more sophisticated, it’s critical that you maintain, test, and regularly update your firewall.

It’s a crucial part of broader penetration testing services, helping ensure your firewall isn’t leaving any gaps for attackers to slip through.

What is Firewall Penetration Testing?

Firewall penetration testing analyzes a firewall’s effectiveness with controlled, simulated cyberattacks. During this test, professionals use tools to test firewall rules, configurations, and efficiency, and then reveal attack results and present their analysis to an end client.

Penetration testers aim to break through your firewall. That means carefully analyzing your security policies and configurations, scanning for open ports, and monitoring network traffic. Once they’ve found potential weaknesses, testers use a range of established hacking techniques to simulate a real-world breach, such as packet manipulation and spoofing, on-path attacks to intercept encrypted traffic, privilege escalation with lateral movements to bypass authorization and segmentation controls.

Why Firewall Testing Is Critical to Cyber Resilience

Routine firewall testing helps you to find hidden vulnerabilities before hackers get to them – protecting your customers’ data, ensuring compliance, and reducing risk to both revenue and your reputation. Additionally, our testers help clients understand their firewalls’ true capabilities and limitations.

Testing is vital to ensure your network and data continue to be protected against emerging threats and stay in line with changing compliance requirements.

Your firewall is a critical first line of defense, but it shouldn’t be left unmonitored or serve as your only protection layer. Experience shows that even enterprise-grade firewalls have vulnerabilities and are only as strong as their configuration for their threat environment:

“A hacker group has leaked data associated with roughly 15,000 Fortinet firewalls and an analysis has shown that it was likely obtained back in 2022 through the exploitation of a vulnerability.

(...)Based on the analysis of the leaked data and a device owned by one of the affected organizations, (Security researcher Kevin) Beaumont determined that it was apparently collected in October 2022, likely through the exploitation of CVE-2022–40684.”

Eduard Kovacs, SecurityWeek

Types of Firewall Penetration Testing

There are two main types of firewall penetration testing – external testing, which judges how effective it is against outside threats, and internal testing, which assesses its security controls from within, and how protective it is against insider threats. At VikingCloud, we offer clients a blend of the two and develop a plan that reflects their data security needs.

There are three main types of testing techniques:

• Black box testing: This is a “blind” assessment where a tester has no prior knowledge of a firewall or associated network.
• White box testing: This is where testers have full details on the firewall they’re attacking, networks attached, and associated systems.
• Gray box testing: This is a blend of black and white box testing.

There are also several techniques used in firewall penetration testing that hackers use to scan for vulnerabilities and test robustness, including:

• Direct traffic tests: This is where testers connect directly to client servers and map out internal networks.
• On-path attacks:  Is where attackers place themselves between users and a firewall to try to hijack traffic.
• Port scanning:  Here, testers use tools to look for open ports and assess whether or not a firewall is blocking routes.
• Rule bypassing: Once testers know more about certain firewall flaws, they will use misconfigurations to sneak into networks.

Steps in Performing Firewall Penetration Testing

There are usually five main steps to performing firewall penetration testing – discussion and reconnaissance, risk analysis, exploitation, reporting, and remediation. However, these steps, and what takes place at each stage, can vary from case to case, and we advise our clients that the process is extremely flexible.

Here’s a quick overview of how a typical firewall test might unfold.

1. Discussion and Reconnaissance: To start, testers discuss what a client needs from the testing process and what to expect. Once the scope is set, testers then use tools to map out the attack surface.
2. Risk Analysis: Testers now try to connect to network systems, analyze traffic flowing in through the firewall, and identify any vulnerabilities they may be able to exploit (such as misconfigurations).
3. Exploitation: Testers now attempt to break through the client’s firewall using their toolkits and vulnerability knowledge. They record all attempts made to bypass the firewall, successful or otherwise.
4. Reporting: Penetration test reports break down what was discovered and what sensitive data might be at risk due to exploitable flaws. Testers inform clients on what to do to fix weaknesses and explain how they broke through.
5. Remediation: Clients follow testers’ advice and make changes to their firewall security. Follow-up tests are recommended at least twice a year to keep ahead of threats.

Tools Used in Firewall Penetration Testing

To augment manual testing of firewall security, simulate sophisticated attack techniques, and mimic hackers effectively, professionals use specialized penetration testing tools such as NMap, Netcat, Hping and TCPreplay. Our testers combine these tools with their expertise, selecting the most appropriate technical approaches based on the project’s unique requirements and scope.

Here’s how some key tools complement our manual testing methodology today:

• Nmap helps testers scan and discover the network topology to find open ports that might allow unauthorized access through the firewall.
• Netcat, known as the "Swiss Army knife" of network utilities, extends our manual testing capability by enabling custom connection requests (such as banner grabbing) to reveal firewall configuration details.
• Hping helps testers to map out architectures by allowing precise packet carfting to probe firewall rule effeciveness, revealing how policies are implemented in practice.
• TCPreplay is a tool that captures and replays network traffic, which helps testers to closely analyze which traffic patterns are permitted and blocked by firewall rules.
• Nessus provides automated vulnerability scanning across various architectures serving as a preliminary step to our in-depth, human-driven penetration testing.

What to Expect in a Good Penetration Test Report

A reliable firewall penetration test report should include a high-level summary of objectives and findings, details on test boundaries and devices interacted with, which types of tests were deployed, and what methodologies or frameworks were used.

Then, a report should also break down any firewall policies or rules relevant to the investigation, and whether or not they were breached. Professional testers will also go into more detail from here on any issues they discovered, how they exploited the firewall, and what data (if any) they were able to access.

All good penetration test reports should conclude with clear recommendations on how to improve firewall security – and what steps clients should take immediately to protect their data.

Conclusion

Like all good security perimeters, your firewall needs regular checks to ensure that it can hold up against some of the biggest cyber threats facing businesses all over the world. Firewall penetration testing is one of the best methods of ensuring that your network and data are safe from hackers and rogue insiders.

If you’d like to know more about how regular penetration testing can help fortify your firewall, get in touch with VikingCloud today for a free consultation.