Unpatched Systems: The Network Vulnerability Hiding in Plain Sight

Every organization knows they should patch their systems. It’s basic security hygiene, right up there with using strong passwords and backing up data.

Yet unpatched vulnerabilities remain one of the most common entry points in actual breaches. Not because patching is complicated or expensive, but because it’s easy to deprioritize until it’s too late.

More than likely, somewhere in your network right now, there’s a system running software with known, documented, easily exploitable vulnerabilities. Attackers know about these vulnerabilities because information is publicly available.

And maybe you’re hoping nobody notices before you get around to patching. Or maybe you are so busy that patches land on the back burner more often than not.

That’s not a security strategy. That’s playing Russian roulette with your network.

Why Unpatched Systems Are So Dangerous

Unpatched vulnerabilities are attackers’ favorite entry point because they’re easy to exploit.

When a software vendor discovers a security vulnerability, they release a patch. At the same time, they publish details about what the vulnerability was and how it works. This is necessary so organizations understand the risk and prioritize patching.

But it also means attackers immediately know:

• Exactly what the vulnerability is
• Which software versions are affected
• How to exploit it
• That any unpatched system is vulnerable

Within hours of a critical patch release, attackers are scanning the internet for vulnerable systems.  Within weeks, automated tools make exploitation trivial even for unsophisticated attackers.

Every day you delay patching is another day you’re vulnerable to attacks that require minimal skill to execute.

The Patching Gaps That Create Risk

Organizations fall behind on patching for predictable reasons.

The “We’ll Patch Next Maintenance Window” Problem

Your team knows a critical patch is available, but deploying it requires downtime or testing. So it gets scheduled for the next maintenance window in two weeks, next month, or next quarter.

Meanwhile, attackers are actively exploiting that vulnerability. They’re not waiting for your maintenance schedule.

The gap between “patch available” and “patch deployed” is when you’re most vulnerable.

The Legacy System Problem

You have systems running old software that can’t be easily updated. Maybe it’s an application that only works on a specific operating system version. Maybe it’s a vendor product that will break if you update dependencies. Maybe it’s a system that “just works,” and nobody wants to touch it.

These legacy systems accumulate vulnerabilities that never get patched. They become permanent weak points in your network.

The “We Didn’t Know It Needed Patching” Problem

Your IT team regularly patches servers and workstations. But that network printer? The VOIP phone system? The building management system? The security cameras? These devices often run on operating systems or firmware that need updates, too, and they’re frequently forgotten.

These overlooked systems become easy targets because no one is maintaining them.

The “Testing Broke Something” Problem

You tested the patch in a development environment, and it broke a critical integration. Now, patching gets delayed while you figure out the compatibility issue.

This is a legitimate concern. Patches do sometimes cause problems, but the solution isn’t to skip them. It’s having processes to test, identify issues, and deploy patches quickly despite complications.

Real Breaches Through Unpatched Systems

Let’s look at how unpatched vulnerabilities lead to actual breaches.

The Exchange Server Attacks

In early 2021, Microsoft released emergency patches for critical vulnerabilities in Exchange Server. These vulnerabilities allowed remote attackers to access email systems, steal data, and install backdoors without any authentication.

Microsoft urged immediate patching, but many organizations delayed.

Within days, tens of thousands of Exchange servers were compromised. Attackers installed web shells, stole email, deployed ransomware, and established persistent access. Some organizations didn’t discover the compromise for months.

The vulnerability was known, and the patch was available, yet organizations that delayed patching were breached. It was that simple.

The WannaCry Ransomware Outbreak

WannaCry ransomware exploited EternalBlue, a Windows vulnerability that Microsoft had patched two months before the outbreak.

Organizations that had deployed the patch were protected. Organizations that delayed patching got hit.

WannaCry spread across networks automatically, encrypting systems and demanding a ransom. It affected hospitals, manufacturers, government agencies, and businesses worldwide, causing damage totaling hundreds of millions of dollars.

The patch was available for two months. Organizations still got breached because they hadn’t deployed it.

The VPN Vulnerabilities

Several VPN products have had critical vulnerabilities discovered in recent years, including Pulse Secure, Fortinet, and Palo Alto. These vulnerabilities allowed attackers to bypass authentication and access internal networks remotely.

Patches were released, and many organizations delayed deployment because VPNs are a critical infrastructure that can’t be down.

Attackers exploited unpatched VPN servers to gain initial access, then moved laterally through networks, stole data, and deployed ransomware. The breach reports consistently note: “The organization had not yet deployed available patches.”

How Attackers Find Unpatched Systems

You might think: “We’re a small organization. Attackers won’t notice our unpatched systems.”

That thinking is wrong. Attackers don’t need to know you exist because they scan the entire internet looking for vulnerable systems.

Automated scanning is constant. Tools like Shodan, Censys, and Masscan continuously scan the internet, cataloging what services are running where. When a new vulnerability is disclosed, attackers immediately scan for systems running affected software. Mass scanning identifies vulnerable systems regardless of organization size. If your server is unpatched and exploitable, it gets targeted whether you’re a Fortune 500 company or a 20-person business.

Vulnerability scanners are free and easy. Tools like Nmap, OpenVAS, and Nessus can scan networks and identify vulnerable software versions. Attackers run these tools against IP ranges to find low-hanging fruit.

Exploit frameworks make attacks trivial. Metasploit and other frameworks include exploits for thousands of known vulnerabilities. Once an unpatched system is identified, exploitation is often a single command. Additionally, automated attacks don’t discriminate. Malware that spreads by exploiting unpatched vulnerabilities doesn’t check company size first. It just exploits whatever vulnerable systems it finds.

Sadly, smaller organizations are easier targets. You likely have fewer security resources, less monitoring, and delayed patching. Attackers know this, so small businesses often get hit with ransomware specifically because they’re seen as easier marks.

Your size doesn’t protect you. Your patching practices do.

The Patch Management Strategy That Actually Works

Effective patch management isn’t complicated, but it requires discipline.

Maintain an Accurate Inventory

You can’t patch what you don’t know exists. Maintain an inventory of all systems, software, and devices on your network. Include servers, workstations, network devices, IoT devices, and any other internet-connected systems.

Be sure to update this inventory regularly as systems are added, changed, or retired.

Monitor for Available Patches

You can subscribe to security bulletins from your software vendors. Use automated tools to identify when patches are available. Many vulnerability scanners can track patch status across your environment.

The goal is to know about critical patches as soon as they’re released, not discover them weeks later.

Test in Non-Production First

Deploy patches to development or staging environments before production, when possible. Verify that critical applications still work. Identify any compatibility issues before they affect production systems.

This doesn’t mean delaying for weeks of testing. For critical vulnerabilities, testing might take a few hours to verify that the patch doesn’t break core functionality.

Automate Where Possible

Use patch management tools to automate deployment where safe to do so. Operating system patches, common applications, and security software can often be automated to deploy on regular schedules.

This reduces the manual burden and ensures patches get deployed consistently rather than when someone remembers.

Have a Process for Legacy Systems

For systems that can’t be patched easily:

• Isolate them on separate network segments
• Restrict network access using firewalls
• Implement additional monitoring
• Have compensating controls to reduce risk
• Document the decision to defer patching and the mitigations in place

Don’t let legacy systems become forgotten vulnerabilities that eventually cause breaches.

Verify Patch Deployment

After deploying patches, verify they are actually installed correctly. Patch deployment sometimes fails silently. Run vulnerability scans to confirm systems are no longer vulnerable.

What to Patch First

If you’re behind on patching and trying to catch up, prioritize:

1. Internet-facing systems: Web servers, VPN gateways, email servers, and remote access systems. These are directly accessible to attackers and need to be patched immediately.
2. Critical infrastructure: Systems that handle sensitive data or provide critical business functions. Compromise of these systems has the highest impact.
3. Operating systems: Windows, Linux, and other OS patches often address vulnerabilities that affect all applications running on those systems. OS patches provide broad security improvements.
4. Widely targeted software: Web browsers, email clients, PDF readers, and office productivity software. These are common attack vectors because they regularly interact with untrusted content.
5. Known exploited vulnerabilities: If a vulnerability is being actively exploited in the wild, it moves to the top of the priority list regardless of what system it affects.

The Penetration Test Reality Check

Want to know if your patching practices are adequate? Get a penetration test.

Penetration testers will scan your systems for known vulnerabilities and attempt to exploit unpatched software, exactly like real attackers would. After that, they’ll look at other exploits that scanners can’t find.

If your systems are properly patched, those attacks fail. If you’re behind on patching, the pen test demonstrates what attackers could exploit.

This provides concrete evidence of risk, helping prioritize patching efforts and justify resources for improved patch management.

Many organizations are surprised by how many unpatched vulnerabilities penetration tests uncover, often on systems they thought were up to date.

The Bottom Line

Unpatched systems are low-hanging fruit for attackers. Known vulnerabilities with public exploit code make compromise trivial for anyone who takes the time to look.

Somewhere in your network, there’s probably a system running software with documented security flaws. Maybe it’s a server you meant to patch last month. Maybe it’s a network device nobody thinks about. Maybe it’s a legacy application that can’t be easily updated.

Attackers will find it. They’re constantly scanning for vulnerable systems. When they find yours, exploitation is easy.

Effective patch management isn’t complicated:

• Know what systems you have
• Monitor for available patches
• Prioritize by risk
• Deploy rapidly for critical issues
• Verify deployment
• Have processes for systems that can’t be patched normally

The gap between “patch released” and “patch deployed” is when you’re most vulnerable. Minimize that gap, and you eliminate one of the easiest ways attackers compromise networks.

Because unpatched vulnerabilities aren’t sophisticated attacks. They’re basic exploitation of known weaknesses that you could have prevented.

Don’t be the organization that gets breached by a vulnerability that was patched months ago.

Test Your Patch Status with MainNerve

MainNerve’s penetration testing includes scanning for unpatched systems and known vulnerabilities across your network. We identify which systems are running vulnerable software versions and demonstrate what attackers could exploit.

Our testing provides concrete evidence of patching gaps, helping you prioritize remediation and justify resources for improved patch management.

We do more than generate a list of missing patches; we show you which unpatched vulnerabilities are exploitable in your environment and what impact they could have on your security.

Ready to find out where your patching gaps are before attackers do? Contact MainNerve to schedule penetration testing that identifies unpatched systems and demonstrates real-world exploit risk.

Because knowing you should patch isn’t enough. You need to know what’s vulnerable right now.

And if you already have a vulnerability scan or pen test and need guidance, reach out to us. We’re happy to assist you with that.