Best free open-source penetration testing tools & vulnerability scanners (2026)

You don't need an expensive subscription to do serious security testing. The open-source ecosystem covers almost the entire workflow — discovery, vulnerability scanning, exploitation and reporting. Below are dependable free, open-source penetration testing tools and vulnerability scanners, grouped by what they do, with an honest note on where each fits. Skip to the comparison table or how to choose.

Network vulnerability scanners

1. ShadowSecurityScanner — exploit-aware network scanner

A free, MIT-licensed network vulnerability scanner that runs as a single desktop app on Windows, macOS and Linux. It does port scanning, service and OS fingerprinting, and thousands of network and web checks, then ranks every finding by EPSS exploit probability and CISA KEV status — so you fix what attackers actually exploit first. Exports PDF, HTML, SARIF, XML and CSV, and diffs scans over time. No cloud, no telemetry, no server to deploy.
Best for: individual pentesters, sysadmins and small teams who want ranked, exploit-aware results with zero setup. Learn more →

2. OpenVAS / Greenbone GVM — server-based scanner

A fully open-source (GPL) vulnerability scanner with a very large feed of network vulnerability tests, deployed as a Linux server stack (scanner, feed sync, database, web UI). Powerful for always-on, centralised scanning, at the cost of setup and maintenance.
Best for: teams wanting a centralised, Linux-hosted scanning server. See our simpler OpenVAS alternative if the stack is too heavy.

3. Nessus Essentials — free tier of a commercial scanner

Tenable's Nessus is the best-known commercial scanner; its free Essentials tier is capped at 16 IP addresses and requires an account. Not open source, but worth knowing.
Best for: home labs and tiny environments already in the Tenable ecosystem. See our free Nessus alternative for an uncapped option.

Network discovery

4. Nmap — network mapping & port scanning

The classic open-source port scanner and host-discovery tool, indispensable for mapping what's alive on a network and which ports and services are exposed. The Nmap Scripting Engine (NSE) adds light vulnerability checks.
Best for: the first step of almost any engagement — reconnaissance and asset discovery. Pairs naturally with a scanner for the deeper checks.

Web application scanners

5. OWASP ZAP — web app scanner & proxy

The OWASP Zed Attack Proxy is a leading free web-app security scanner and intercepting proxy — ideal for finding injection, broken access control and other web issues, and for manual testing of sites and APIs.
Best for: testing web applications and APIs, both automated and hands-on.

6. Nuclei — template-based scanning

A fast, community-driven scanner that runs YAML templates against targets. Its template corpus is so widely used that ShadowSecurityScanner incorporates Nuclei templates into its own active web probes.
Best for: fast, scriptable checks across many hosts and CI pipelines.

7. Nikto — web server scanner

A long-standing open-source web server scanner that checks for thousands of dangerous files, outdated software and misconfigurations. Noisy but useful for a quick server-hygiene pass.
Best for: a fast baseline sweep of a web server's known issues.

8. sqlmap — SQL injection testing

The de-facto open-source tool for detecting and exploiting SQL injection, with deep database fingerprinting and data-extraction capabilities.
Best for: confirming and demonstrating SQL injection impact during a test.

Exploitation & validation

9. Metasploit Framework — exploitation toolkit

The open-source Metasploit Framework is the standard toolkit for validating vulnerabilities with real exploits and post-exploitation modules — the step that turns a scanner finding into proven impact.
Best for: exploitation and proof-of-impact in authorized engagements.

Container & supply-chain scanning

10. Trivy — container, IaC & dependency scanner

A popular open-source scanner for container images, filesystems, IaC and dependencies, surfacing known CVEs and misconfigurations. Fits neatly into CI/CD.
Best for: DevSecOps pipelines scanning images and infrastructure-as-code.

Honourable mention: Wireshark — the standard open-source packet analyser, invaluable for inspecting traffic during testing.

Comparison at a glance

How to choose

• Mapping a network? Start with Nmap.
• Want ranked, exploit-aware findings with zero setup? ShadowSecurityScanner.
• Need an always-on Linux scanning server? OpenVAS / GVM.
• Testing web apps and APIs? OWASP ZAP, plus Nuclei for templated checks and sqlmap for SQLi.
• Proving impact? Metasploit Framework.
• Securing containers & pipelines? Trivy.

A realistic free stack for internal testing: Nmap for discovery → ShadowSecurityScanner for ranked network vulnerability scanning → OWASP ZAP / Nuclei for web apps → Metasploit to validate the findings that matter. See how to run a network vulnerability scan for the end-to-end workflow.

Related guides

• How to run a network vulnerability scan.
• What are EPSS and CISA KEV?
• ShadowSecurityScanner vs Nessus vs OpenVAS.
• Free Nessus alternative · OpenVAS alternative.