Top 10 Open‑Source Security Tools Every Professional Should Know

In fact, whether learning, experimenting, or deploying in production, security professionals have long considered open‑source software an essential part of their toolkit. Below we recommend ten open‑source security tools you should know and use.

Nessus

Nessus is currently the most widely used system vulnerability scanner and analyzer worldwide. According to sectools.org, Nessus is the most popular vulnerability scanner and the third most widely used security program.

Nessus offers both free and commercial editions. The current version, Nessus 7.1.0, is a commercial version that is free for personal home use. The 2005 version remains open‑source and free.

Although Tenable retained version 2, it has been forked in several directions. Nessus knowledge remains a valuable professional skill.

Snort

Just as thousands of IT security professionals first learn vulnerability scanning with Nessus, Snort has always been the starting point for intrusion detection system (IDS) knowledge.

Snort operates in three modes: sniffer, packet logger, and network intrusion detection system, making it either the core of an automated security system or a component of commercial products.

Snort is now owned by Cisco and continues to be developed by an active community. It is a must‑know open‑source tool for security practitioners.

Nagios

Nagios is an open‑source free network monitoring tool that can effectively monitor hosts on Windows, Linux, and Unix, as well as switches, routers, printers, and other network devices. Like many open‑source packages, Nagios offers both free and commercial editions.

Nagios Core is the open‑source core of the project. It can be extended with plugins to monitor individual services or perform specific tasks; about 50 official plugins and over 3,000 community‑contributed plugins are available.

The Nagios user interface can be accessed via desktop, web, or mobile front‑ends, and configuration can be managed through various available tools.

Ettercap

If you need to test your enterprise network against man‑in‑the‑middle (MITM) attacks, Ettercap is the tool of choice. Since its first release in 2001, the project has focused on launching MITM attacks.

Ettercap currently supports four basic attack modes: IP‑based, MAC‑based, and two ARP‑based strategies. During scanning and testing, Ettercap provides extensive information about the network and its devices, making it an excellent component of a comprehensive security toolkit.

Infection Monkey

Infection Monkey, released by Israeli security company GuardiCore at the 2016 Black Hat conference, is a data‑center security testing tool that automates the assessment of boundary and internal server security.

Its user interface is a notable feature; unlike many open‑source security projects that provide minimal UI or rely on GUI plugins, Infection Monkey offers a GUI comparable to commercial tools. The source code is available on GitHub.

Delta

Compared with traditional network security testing, security issues in software‑defined networking (SDN) are still emerging. Delta was created to address this gap.

As an Open Networking Foundation (ONF) project, Delta searches for potential problems in SDN, explores them, and helps determine their exploitability. It includes built‑in fuzzing to discover known or unknown network vulnerabilities.

Delta’s code and binaries are available on GitHub.

Cuckoo Sandbox

Cuckoo Sandbox is a well‑known open‑source sandbox system for safely testing files. Built on a virtualized environment, it automatically executes and analyzes malicious program behavior.

The Sleuth Kit

Understanding what happened during an attack is often the key to preventing future intrusions. The Sleuth Kit is an open‑source digital forensics tool that can recover lost files from disk images and perform disk‑image analysis for special events.

Autopsy provides a web interface for the Sleuth Kit, supporting all its features on both Windows and Linux platforms, and enjoys a large, active user community.

Lynis

Lynis is a Unix security auditing and hardening tool that performs deep scans to detect potential issues and provide recommendations for future system hardening. It examines system information, vulnerable packages, and misconfigurations.

The Lynis code is hosted on GitHub and maintained by its creator, Cisofy. Because it is Unix‑based, Lynis can also scan and assess popular IoT development boards such as the Raspberry Pi.

Certbot

Encryption is crucial for many security standards, but implementing it can be complex and costly. The Electronic Frontier Foundation (EFF) aims to simplify this with tools like Certbot, an open‑source automated client that obtains and deploys SSL/TLS certificates for web servers.