Stop 13 · Security Tools & AutomationTopics · 3/8

Vulnerability Scanners (Nessus, OpenVAS)

In short

Hundreds of machines, thousands of known flaws. Vulnerability scanners check your systems against a big database of known issues, so you know what to patch before attackers find it.

Automated tools that scan systems and networks for known vulnerabilities at scale — a core recurring activity for identifying what needs patching before attackers find it first.

The blob as a doctor listens to a friendly computer tower with a stethoscope.

Think of it like this

The annual health checkup

At a full body checkup, the lab runs a fixed set of tests and flags anything outside the normal range. It does not treat you, and some flags are false alarms. A doctor still reads the report. Scanners work the same way for your servers.

Watch it happen

One scan cycle

Permission

Discover

Check

Report

Fix

Rescan

1/6Get written approval and an agreed scope: which IP ranges, which time window, who to call if something breaks.

The big ideas

What you need to know

Credentialed scans see more

A scan that logs in with a read only account can check installed packages exactly. Unauthenticated scans only see the outside.

False positives happen

A scanner may guess a version wrong. Validate important findings before raising alarms.

Tool options

Nessus is commercial with a free Essentials edition for small labs. OpenVAS is open source, part of Greenbone Community Edition.

Scan regularly

New CVEs appear daily. A scan from three months ago does not describe your systems today.

Save yourself the pain

Common mistakes

Oops

Scanning a network you do not own because it seemed harmless.

Do this instead

Scanning without permission can be illegal and can crash fragile systems. Always get written approval and a defined scope.

Oops

Sending the raw 400 page scan report to every team.

Do this instead

Validate, group and prioritise first. Give each owner a short list of what to fix and why.

Your mission

Scan your own lab VM

~45 min

Quick check

Why do credentialed scans usually find more real issues than unauthenticated ones?

Go deeper

1Run a free vulnerability scanner (like OpenVAS) against a practice lab environment.
2Learn to prioritize scan findings by severity and exploitability, not just raw count.
3Understand why regular, scheduled scanning matters more than a one-time assessment.