Strengthening Cybersecurity with External Network Penetration Testing

Introduction to External Network Penetration Testing

As the Director of Tanner Security, I’ve seen how fast cyber threats change and evolve. A few years ago, we were doing a project with a nonprofit that handled sensitive donor information. They thought they were too small to be targeted. However, during external network penetration testing, we found a weak password on their email system that could have allowed a hacker access to years of private data. That discovery changed the way their managers thought about security.

Stories like that remind me that cybercriminals don’t care how big or small your company is. They are constantly scanning for easy opportunities. External network penetration testing, often called “net pen testing,” helps uncover those vulnerabilities before attackers do. It’s one of the most effective ways to safeguard your systems, data, and reputation.

Why Testing Matters

Last year, we performed an IT risk assessment for a financial services client, and their management team thought their IT controls were airtight. They had firewalls, antivirus tools, and strong policies in place. But when we performed an external pen test, we found that an old, forgotten web application was still running and hadn’t been patched in years. It took less than five minutes to gain access through that system. The client was shocked. Until then, they thought of pen testing as a “nice-to-have.” Afterward, they told me it was the best investment they had ever made in cybersecurity.

The reality is that data breaches are expensive and damaging. Today’s average cost of a breach is estimated at $4.45 million, factoring in technical recovery and reputational harm, legal fees, and lost trust. Penetration testing costs a fraction of that, yet it provides invaluable insight into where your IT controls are effective and strong, and where they aren’t.

What External Network Penetration Testing Looks Like

We use the same tactics and tools as the attackers when conducting external network penetration tests. For example, phishing is still one of the easiest ways to get into a network. In one test, we sent a simulated phishing email to a client’s staff, and within minutes, an employee clicked the link and entered their login information. That one mistake could have compromised the entire network. It was a wake-up call for the company, leading to company-wide training that dramatically strengthened their employees’ understanding.

Passwords are another common weakness. I’ll never forget when we cracked an administrator’s password in under two minutes because it was simply the name of their favorite sports team with “123” at the end. That administrator had access to almost everything in the system. It was eye-opening for leadership to see how one weak link could put so much at risk.

We also look for technical flaws like unpatched servers, open ports, and outdated software. These may sound minor, but attackers often build their entire strategy around small oversights. In one assessment, we found a misconfigured firewall that would have allowed an attacker to bypass the client’s IT controls entirely.

A Real-World External Network Penetration Testing Case Study

One of the most memorable projects I’ve worked on was with a mid-sized healthcare provider. They had invested heavily in security tools but had never conducted a full external penetration test. From the outside, everything looked well-defended. But once we started digging, we uncovered an overlooked development server still connected to their production environment.

The server was running outdated software and had several unpatched vulnerabilities. Using those, we could gain initial access and, within hours, escalate privileges to a point where we could view sensitive patient data. Naturally, we stopped short of accessing it, but we documented the path an attacker could have taken.

When we presented our findings, the leadership team was stunned. They had assumed their biggest risks came from phishing attacks or insider threats, but this hidden server posed an even greater risk. Because of the test, they immediately decommissioned the vulnerable system, updated their patching procedures, and restructured their network segmentation to ensure sensitive data could never again be reached so easily.

Six months later, they told us that the test had improved their technical defenses and boosted confidence among their staff and patients. Knowing that vulnerabilities were identified and fixed gave their community trust that security was being taken seriously.

The Process

A penetration test isn’t about embarrassing IT departments but empowering them. We start by working with leaders to set goals and define what should be tested. The process then moves into reconnaissance, where we gather information that attackers could find. After that, we test those entry points to see if they can be exploited.

The part that often surprises leaders most is the report at the end. We don’t just hand over a list of vulnerabilities, we show the exact steps an attacker could have taken and explain how to fix them. I’ve seen the relief on a client’s face when they realize, “Yes, we had weaknesses, but now we know how to close them.” That’s what makes the process worthwhile.

Tanner Security’s Approach

At Tanner Security, we treat every client as a partner. Our goal isn’t to scare anyone but to give them clarity and confidence. We explain our findings in plain English and stick around to help with remediation.

One of my favorite moments is when clients tell me, “We sleep better at night now.” That’s the real value of external network penetration testing. It’s not just about systems and software; it’s about giving leaders and employees peace of mind that their organization is protected.

Conclusion

External network penetration testing is one of the best investments a company can make in its cybersecurity program. It’s a chance to see your systems the way attackers see them, and to close the gaps before they’re exploited.

I’ve worked with nonprofits, businesses, and government organizations of every size, and the lesson is always the same: proactive testing saves time, money, and trust. Don’t wait for a breach to reveal your weaknesses. Take the proactive step now, and let’s make sure your defenses are ready for whatever comes next.