- Hack The Box (https://www.hackthebox.eu/)
- CTFtime (https://ctftime.org/)
- OverTheWire (https://overthewire.org/wargames/)
- PicoCTF (https://picoctf.org/)
- Root-Me (https://www.root-me.org/)
- VulnHub (https://www.vulnhub.com/)
- TryHackMe (https://tryhackme.com/)
- PentesterLab (https://pentesterlab.com/)
- CTFlearn (https://ctflearn.com/)
- RingZer0 Team Online CTF (https://ringzer0ctf.com/)
- CTFtime (https://ctftime.org/)
- Reddit CTF (https://www.reddit.com/r/ctf/)
- Twitter (Hashtags: #CTF, #CaptureTheFlag)
- CTF Write-ups (https://github.com/ctfs/write-ups)
- Capture The Flag Live (https://ctf.live/)
- CTF Field Guide (https://trailofbits.github.io/ctf/)
- CTF Wiki (https://ctf-wiki.github.io/ctf-wiki/)