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20. Vulnerability Scanning and Assessment

20.4 OpenVAS / Greenbone: Full Vulnerability Scanning

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OpenVAS (now part of Greenbone Community Edition) is a free, full vulnerability scanner. It has tens of thousands of tests (called NVTs) and checks versions, configurations and weak settings, then gives a report with CVSS scores and fixes. Commercial tools like Nessus and Qualys work in a similar way.

Install on Kali (needs about 4 GB RAM for the Kali VM and time to download the feeds):

sudo apt update && sudo apt install -y gvm      # Kali is Debian-based, so it uses apt, not yum
sudo gvm-setup                                   # first-time setup; downloads feeds (can take a long time)
                                                 # note the admin password printed at the end
sudo gvm-check-setup                             # verifies everything is ready
sudo gvm-start                                   # start the services

Open https://127.0.0.1:9392 in Firefox inside Kali and log in as admin with the printed password.

Run a scan:

  1. Configuration, Targets, New Target: name Metasploitable2, hosts 192.168.56.20.
  2. Scans, Tasks, New Task: choose the target and the scan config Full and fast.
  3. Start the task and wait (20–60 minutes for one host).
  4. Open the Report: results are sorted by severity, each with a description, affected versions, CVEs and a Solution section.

Scanners can break things

Some checks send unusual data that may crash old services. That is why we scan only a lab VM with a snapshot. In a real job, full scans are agreed in the scope document and often run in a maintenance window.

Ravindra Bagale's Tip

gvm-setup takes a long time, and students shut down the VM in the middle – then the setup breaks. Go and have a cup of tea, but don't stop it! Also, if the Kali VM has too little RAM, the scanner hangs. Give it at least 4 GB.

Lab

Install Greenbone on Kali, run a "Full and fast" scan against 192.168.56.20, and export the report as PDF. Count how many Critical, High, Medium and Low findings you got.

Extended teaching notes

Why this lesson matters

Use this lesson to strengthen systems you own: understand the risk, practise safely in a lab, then write and apply the fix.

Apply the fix across stacks

Same class of bug, same idea in every language.

Java / Spring Boot

Parameterise queries, encode output, CSRF tokens, limited Actuator, dependency scanning.

ASP.NET Core

EF Core / parameterised SQL, Razor encoding, HTTPS, Data Protection.

Node.js / Express

helmet, parameterised SQL, npm audit, avoid eval and shell concat.

Python / Django / Flask / FastAPI

ORM, autoescape, pip-audit, Bandit; never shell=True with user input.

PHP / Laravel

PDO/Eloquent, Blade escaping, composer audit.

Go / Ruby

database/sql placeholders / ActiveRecord; html/template / ERB escaping; govulncheck / Brakeman.

nginx / Apache / Tomcat

Hide versions, TLS, security headers, least-open ports.

MySQL / PostgreSQL / MongoDB / Redis

Private networks, auth on, least-privilege users, no 0.0.0.0/0.

AWS / Azure / GCP

Roles not long-lived keys, private data stores, cloud audit logs on.

Mini case study

Suppose we are on a purple-team exercise for an Indian mid-size company (sample data). Red notes a technique from this lesson against a lab clone. Blue must show the control that stops it, the log that would have fired, and the ticket that hardens production. That is the standard this course trains you for.

Defender's worksheet (do this today)

  1. Write the lesson title, date and the exact lab target you are allowed to use.
  2. List three owned systems (VMs, apps, or cloud accounts) where this lesson applies.
  3. Run one safe check from the lesson on a lab system only. Paste the command and output.
  4. Write a two-sentence fix you would give a teammate.
  5. Name one related public advisory (CERT-In, CISA, NVD, or a vendor bulletin) with its date.

Indian workplace (sample data)

Suppose we are a junior analyst at Infosys, TCS, Wipro or a fintech SOC in Bengaluru/Pune. Turn this lesson into one checklist item with an owner, a due date and a place to store evidence (ticket + screenshot).

Global practice

Compare your notes with OWASP, CIS Benchmarks, NIST CSF/IR guidance or a cloud Well-Architected security question. Write five lines on what overlaps.

Everyday analogy

Explain the risk and the fix to a family member without jargon. If they can repeat the warning, you understand it well enough to teach juniors.

Key terms

  • Control: a safeguard (patch, config, process, detection).
  • Finding: a weakness backed by evidence.
  • Remediation: the fix plus how you verified it.
  • Scope: systems you have written permission to touch.
  • Least privilege: only the access the task needs.
  • Defence in depth: several layers so one failure does not end the story.

Common mistakes

  • Skipping written permission "just for a quick scan".
  • Practising on hostel, office or public targets without authorisation.
  • Collecting tool output without writing the fix.
  • Copying attack steps onto production to "verify". Defenders verify with versions, configs and patches.
  • Publishing screenshots that contain secrets, cookies or internal hostnames.

Recap

  • Evidence, fix, owner, date.
  • Own lab only.
  • Fix > spectacle.