The following lists are free services, open-source software and software lists, and other free resources available to any organization, tailored to the “Blue Team”, the defenders.

We provide these “As-Is” and without official endorsement or warranty.

Free CISA Services

• CISA’s CyberHygine Service: free vulnerability scanning of any publicly available systems
• CISA’s Free Services webpage
• CISA’s Public Learning Portal: Free virtual cybersecurity training for the public. Register using a login.gov account.
  • If you used FedVTE in the past, this is its replacement.
• ICS/OT Training Portal: Free virtual training on ICT/Operational Technology ran by Idaho National Laboratory. Open to the public, register using a login.gov account

Free Software Lists

These are community-maintained lists of free or open-source software organized by usecase and function:

The following lists are free training services, open-source software and software lists, and other free training resources. We provide these “As-Is” and without official endorsement or warranty.

Administration and Troubleshooting

• Sad Servers: “LeetCode for Linux” - learn to troubleshoot and fix broken Linux servers.
• RegExr: Learn to write and test Regular Expressions (RegEx)
• Learn DMARC: Learn the importance of setting up DMARC for your email domain
• Killer Shell: simulators for Linux Foundation Exams
• RHCSA Practice Questions: practice questions for version 7 of the Red Hat Certified System Administrator exam. These are useful to anyone looking to practice Linux administration skills.

“Capture The Flag” sites

• OverTheWire’s Wargames: fantastic for beginners to CTFs and pentesting
• UnderTheWire: more free CTF machines
• Gandalf AI: prompt injection CTFs on a real generative AI system
• Awesome-CTF: Aggregated list of different CTF Sites
• HackTheBox: one of the biggest and most comprehensive CTF sites on the internet
• TryHackMe: Similar to HackTheBox but more educational and open-ended solutions

Cybersecurity

• Clark.Center: huge platform of free cybersecurity curriculum

Programming and Scripting

• Python Automate The Boring Stuff: practical Python Programming for total beginners

Intentionally Vulnerable VMs and Software

These are sites with software and virtual machines created to be intentionally vulnerable to test your pentesting skills or demonstrate vulnerabilities.