Open source software is an attractive option for many IT leaders and teams, especially at small and mid-sized organizations. Instead of paying large licensing fees to an enterprise software vendor, your team can customize the source code of free open source platforms and security tools. 

The overall market for open source software services market was worth $30 billion in 2023 and is estimated to hit nearly $120 billion by 2032. That translates to an annual compound growth rate of 16%: 

Source: Global Market Insights

Cybersecurity tools corner a large market share of open source software. There are plenty of free open source cybersecurity tools that meet requirements for enterprise-grade security software. 

Many of these free open source security tools do not offer the same capabilities as the paid enterprise alternative. Some cybersecurity professionals use open source solutions to test a wide range of options before deciding on the full enterprise security tool they want to integrate. 

However, since you can modify the code base of open source security solutions, they may offer greater flexibility than some commercial tools. In this case, it's up to your security team to customize that tool to meet the needs of your unique security posture.  

Small and mid-size enterprises often use a combination of free and paid open source tools to improve their organization's cybersecurity in a cost-effective way. Customizing open source solutions to protect digital assets and networks reduces the need to pay licensing fees, but you'll still pay for the infrastructure they use to host and manage those tools. 

10 open source cybersecurity tools you should know 

1. Kali Linux

Kali Linux is an open source Debian-based Linux distribution offering a variety of free software, cyber security utilities and penetration testing tools. It is one of the main open source penetration testing tools that new ethical hackers use to hone their craft. 

It is one of the few hacking-focused Linux distributions that comes pre-packaged with tools for reconnaissance and delivering payloads, as well as several other penetration-testing utilities. Use Kali Linux to test cybersecurity postures, discover security vulnerabilities, and conduct ethical hacking operations. 

Kali uses WSL (Windows Subsystem for Linux), which allows users to run Linux executable files directly from a Windows 10 system. The Kali OS supports embedded devices such as Raspberry Pi, Beaglebone, Odroid, HP & Samsung Chromebook as well as popular mobile device operating systems like Android OS. 

2. KeePass

KeePass is a free and open source password manager that securely stores passwords. This security tools enables users to have a single place for their unique passwords for websites, email accounts, webservers or network login credentials. 

KeePass works by storing passwords in a secure database, which unlock by entering a single master key. Database encryption is using the most secure encryption algorithms available: AES-256, ChaCha20 and Twofish. It encrypts the complete database, which means user names, notes, and more are encrypted along with the password fields. 

Like many open source access management and network security tools, KeePass comes under a freemium model. You can download and use the basic version of the tool for free, but you'll need to pay for the commercial version if you want an advanced range of features like a one-time password generator or built-in browser extension. 

3. Metasploit Framework

Metasploit is an exploitation and vulnerability validation tool that you can use offensively to test your systems for known and open vulnerabilities. As one of the most popular open source vulnerability scanners available, independent security professionals often use it for security auditing and network security assessments. 

This security tool helps you divide the penetration testing workflow into manageable sections. You can also use it to set up your own workflows. Since it is owned by Rapid7, some of its more valuable security workflows are only available through the commercial solution. 

Metasploit enables security teams to conduct a wide range of techniques for auditing and network port scanning, which scans about 250 ports usually exposed to external services. An auto-exploitation feature works by cross-referencing open services, vulnerability references and fingerprints to find corresponding exploits. It supports a variety of platforms but is particularly well-suited to testing web server components in mid-sized Linux environments. 

4. Nikto

Nikto is a free and open source web server scanner, which scans web servers for multiple vulnerabilities. The testing covers thousands of potential vulnerabilities and harmful files, and additionally conducts patch management for more than a thousand web server systems. The web server scanner finds version-specific problems on hundreds of different servers. 

Users can also perform checks for server configuration issues such as the presence of multiple index files and HTTP server options. This open source security tool identifies installed web servers and software as well. 

Nikto uses a command-line interface, which makes it well-suited for technically competent security consultants and auditors. However, the project is not a large, well-funded institution, and the package of exploit rules you need to use Nikto effectively is not free. This extra hidden cost can make it less attractive to cybersecurity experts who expect a fully open source vulnerability scanning solution  

5. Nmap

Nmap—also called Network Mapper—is used for penetration testing and security auditing. It uses NSE scripts to detect vulnerabilities, misconfigurations and security issues concerning network services. 

Nmap discovers network and ports before a security audit starts and then uses the scripts to detect any recognizable security problems. The app fetches raw data and then determines a host type, type of operating system (OS) and all the hosts available within the network. 

Network administrators can use Nmap also for performing tasks around network inventory, service upgrade schedules and monitoring uptime. It is commonly included in educational courses that focus on cybersecurity technical skills, so many cybersecurity teams are already familiar with it.   

The open source security tool runs on Linux, Windows and Mac OS X. While it does have a graphical user interface, most security professionals and penetration testers prefer the command-line tool. It is designed specifically for scanning large networks but can be used to scan single hosts. 

6. OpenVAS

OpenVAS is an open source and full-fledged vulnerability scanner, free for use. Users can perform unauthenticated testing and authenticated testing for various high level and low-level Internet and industrial protocols. 

This tool also enables performance tweaking for large-scale scans. Users can perform any type of vulnerability test by taking advantage of its internal programming language. 

OpenVAS provides comprehensive vulnerability scanning capabilities for a free solution, and it is supported by an active online community. However, it can be overwhelming for inexperienced users and its interface is not the most modern. 

7. OSSEC

OSSEC is an open source, scalable and multi-platform Host-based Intrusion Detection System (HIDS) that allows organizations to detect malicious activities and analyze security incidents effectively. 

Use OSSEC on-premises and in the cloud for the purpose of server protection or as a log analysis tool that monitors and analyzes firewalls, IDSs, web servers and authentication logs. 

OSSEC can withstand cyberattacks and system changes in real-time utilizing firewall policies, integration with third parties such as CDNs and support portals. The application features self-healing capabilities and provides application and system-level auditing for compliance with many common standards such as PCI-DSS and CIS. 

OSSEC can be combined with other open source tools to create a functioning Security Information and Event Management (SIEM) solution. Although the process is complex, you can equip it with customized threat detection rules and even add machine learning support for basic behavioral analytics. 

8. Security Onion

Security Onion is a Debian-based Linux distribution for detecting threats, enterprise security monitoring and log management. True to its name, it incorporates multiple layers of security tools such as Elasticsearch, Logstash, Kibana, Snort, Suricata, Zeek, OSSEC, Wazuh, Sguil, Squert, NetworkMiner and others to protect an organization against cyber threats. 

It is an all-in-one open source security solution that provides users with various tools to detect threats and monitor their systems, but it relies on a wide variety of third-party open source tools. This adds to the complexity of running operational security systems with Security Onion, since you'll need a technically competent team capable of handling potential security issues across the entire tech stack. 

9. VeraCrypt

VeraCrypt is a security tool for disk encryption. It runs on Windows, Mac OSX and Linux and creates a virtual encrypted disk within a file before mounting it as a real disk. 

This tool encrypts an entire partition or storage device such as a USB flash drive or hard drive before dumping it the cloud or elsewhere. Users can also pre-boot authentication by encrypting a partition or drive where the Windows OS is installed. 

VeraCrypt encrypts in real-time and supports hidden drives and hidden operating systems on a machine. However, misconfigurations can cause critical file failures and other undesired results. Since VeraCrypt doesn't perform file-by-file encryption, making a change to a single file in a partition will invalidate the entire disk image. Synchronizing encrypted backups with VeraCrypt can be a time-consuming process. 

10. Wireshark

Wireshark is a free and open source tool for network protocol analysis. This cybersecurity tool enables security professionals to observe network traffic at a deep level. It shows each element of individual data packets, allowing analysts to identify the packet format and troubleshoot network issues with great accuracy. 

It is available for multiple platforms including Windows, Linux, and macOS. It supports deep inspection of hundreds of protocols, live capture, and offline analysis of network data. Advanced users can decrypt multiple protocols including IPsec, ISAKMP, Kerberos, SNMPv3, SSL/TLS, WEP, and WPA/WPA2. 

Since Wireshark is designed for manually investigating individual network connections and assets, it does not offer the level of visibility of a full-featured Network Detection and Response (NDR). It is more of a tool for observing specific instances of network traffic in response to potential threats or other issues.