I have been doing this long enough to know that the price tag on a security tool does not determine how useful it actually is. Some of the most powerful scanners I run on a regular basis cost me exactly nothing.
A few years ago a client called me in a panic. Someone had gotten into their server and they had no idea how long the door had been open. After we cleaned things up I asked them when they last scanned for vulnerabilities. They looked at me like I asked them if they brushed their teeth that morning. That is when I started being very intentional about recommending free tools to people who think security scanning is only for big companies with big budgets.
The truth is you do not need to spend money to get a solid picture of where your network or application is exposed. What you do need is the right tools and a basic understanding of what you are looking at. I am going to walk you through the exact free tools I keep in my own kit and how I actually use them.
Starting with your network: Nmap
Nmap (Network Mapper)
Free, open source network scanner — nmap.org
If you are only going to learn one tool from this list, learn Nmap. It has been around since 1997 and it is still the first thing I open when I want to understand what is running on a network. Nmap scans ports, identifies operating systems and detects services running on machines. Think of it as shining a flashlight into a dark room to see what furniture is in there before you trip over something.
I use it in two main ways. The first is a quick scan just to see what devices are alive on the network. The second is a more detailed service version scan where I want to know exactly what software is listening on which port and what version it is running. That version information is critical because old versions of services are usually where the real problems hide. I once ran a version scan on a small office network and found an ancient version of OpenSSH on a device nobody remembered setting up. That kind of thing happens more than you would think.
You run it from the command line and the syntax is simple once you get a few scans under your belt. Start with a basic scan of your own IP range before you ever point it at anything else. That alone will teach you things about your own environment you probably did not know.
Web application scanning: Nikto
Nikto
Open source web server scanner — github.com/sullo/nikto
When someone tells me they just launched a website or a web app, my immediate next question is whether they have scanned it yet. Most people have not. Nikto is a free web server scanner that checks for common vulnerabilities, outdated software, dangerous files and misconfigured headers. It is not subtle but it does not need to be. It is designed to be fast and loud because you are running it on systems you own.
What I like about Nikto is that it does not require you to understand complex configuration before you can start using it. You point it at a URL and it reports back what it finds. On one scan for a small business client I found that their web server was exposing a phpinfo file that revealed their entire server configuration to anyone who knew where to look. That is the kind of low-hanging fruit that attackers love and Nikto catches it immediately.
It runs inside Kali Linux by default and on any system where Perl is installed. The output is easy to read and it actually tells you why each finding matters. That part is helpful if you are working with someone who is not technical and needs to understand what they are looking at.
Full vulnerability scanning: OpenVAS
OpenVAS / Greenbone Community Edition
Open source vulnerability scanner — greenbone.net
OpenVAS is the heavy lifter on this list. It is a full vulnerability scanner that checks systems against a database of known CVEs and misconfigurations. Setup takes a bit more effort than the other tools here but once it is running you get a level of detail that rivals paid enterprise scanners. I have used commercial tools that cost thousands of dollars a year and OpenVAS has caught things those tools missed.
It runs as a web interface so you set up a scan target, schedule the scan and come back to a full report. The reports are detailed and include a risk score for each finding so you know what to fix first. That priority information is important because in a real environment you are never going to fix everything at once. You want to know what is actively dangerous versus what is just technically out of compliance.
I usually recommend OpenVAS for internal network assessments. If you are a small IT team trying to build a vulnerability management process without a big budget this tool gives you a legitimate foundation to build on. The initial setup on a fresh Linux box takes maybe an hour. After that the ongoing maintenance is minimal.
Checking SSL and TLS configurations: testssl.sh
testssl.sh
Free shell script for TLS/SSL testing — testssl.sh
A lot of people assume that having HTTPS means their site is secure. That assumption has gotten many organizations into trouble. HTTPS means the connection is encrypted but the quality of that encryption depends entirely on how TLS is configured. Weak cipher suites, expired certificates and support for outdated protocol versions like TLS 1.0 are all vulnerabilities that live inside what looks like a secure HTTPS connection.
Testssl.sh is a shell script that runs right in your terminal and checks all of that. It tests your certificate, checks for known vulnerabilities like Heartbleed and POODLE, and tells you exactly which cipher suites your server supports. I run this on every server before I sign off on a deployment and it has saved me from embarrassing oversights more than once. One time I almost let a server go live with TLS 1.0 still enabled because a legacy application required it temporarily and it just never got turned off.
You do not need to install anything. You just download the script, make it executable and run it against a hostname or IP. The output is color coded so it is very readable even if you are not deep into TLS mechanics. Green is good, red means fix it now.
Passwords and exposed credentials: Hydra and Have I Been Pwned
THC Hydra + Have I Been Pwned
Password auditing + breach lookup — github.com/vanhauser-thc/thc-hydra & haveibeenpwned.com
I want to be clear upfront: Hydra is a tool for testing login systems you have explicit permission to test. I use it to verify whether accounts on internal systems are protected by strong credentials. It supports a huge number of protocols including SSH, RDP, FTP, HTTP forms and more. Running a controlled brute force test against your own login pages with a common password list is one of the most eye-opening exercises you can do.
I pair Hydra with Have I Been Pwned which is a free service that tells you whether an email address or password has appeared in a known data breach. Before I do any password audit I have the client check their employee email addresses through HIBP first. You would be surprised how often you find that a company email is sitting in a breach dump with its original password still in use on internal systems. That combination of a known password and an active account is exactly what attackers look for.
These two tools together give you a very honest look at the credential hygiene situation in any environment. It is uncomfortable to see but better to know than to find out the hard way.
Putting it all together
None of these tools is a magic button. You still need to understand what you are looking at and what to do with the results. But that is actually the point. Learning to use free tools like these forces you to engage with the findings rather than just reading a PDF from an automated commercial platform and filing it away.
My usual workflow for a basic vulnerability assessment starts with Nmap to map the environment. Then I run OpenVAS against internal systems and Nikto against any web-facing services. I check SSL configurations with testssl.sh and wrap up with a credential review using HIBP and where appropriate a Hydra test on login surfaces. That entire process costs nothing except time and it gives a genuinely useful picture of where the risks are.
If you are just getting started I would say pick one tool, Nmap is the best first choice, and spend a weekend getting comfortable with it on your own home network. You will immediately start seeing things you did not know were there. That curiosity is what eventually turns someone into a decent security professional. The tools are all out there. Most of the hard work is just in actually sitting down and running them.
Got questions about any of these tools or how to interpret a scan result? Drop them below. I check comments when I can and I am happy to help you make sense of what you are seeing.
