1. CTF365On CTF365 users build and defend their own servers while launching attacks on other users’ servers. The CTF365 training environment is designed for security professionals who are interested in training their offensive skills or sysadmins interested in improving their defensive skills. If you are a beginner to infosec, you can sign up for a free beginner account and get your feet wet with some pre-configured vulnerable servers.
2. OVERTHEWIREOverTheWire is designed for people of all experience levels to learn and practice security concepts. Absolute beginners are going to want to start on the Bandit challenges because they are the building blocks you’ll use to complete the other challenges.
3. HACKING-LABHacking-Lab provides the CTF challenges for the European Cyber Security Challenge, but they also host ongoing challenges on their platform that anyone can participate in. Just register a free account, setup vpn and start exploring the challenges they offer.
4. PWNABLE.KRpwnable.kr focuses on ‘pwn’ challenges, similar to CTF, which require you find, read and submit ‘flag’ files corresponding to each challenge. You must use some sort of programming, reverse-engineering or exploitation skill to access the content of the files before you are able to submit the solution.
They divide up the challenge into 4 skill levels: Toddler’s Bottle, Rookiss, Grotesque and Hacker’s Secret. Toddler’s Bottle are very easy challenges for beginners, Rookiss is rookie level exploitation challenges, Grotesque challenges become much more difficult and painful to solve and, finally, Hacker’s Secret challenges require special techniques to solve.
5. IOIO is a wargame from the createors of netgarage.org, a community project where like-minded people share knowledge about security, AI, VR and more. They’ve created 3 versions, IO, IO64 and IOarm, with IO being the most mature. Connect to IO via SSH and you can begin hacking on their challenges.
6. SMASHTHESTACKSmashTheStack is comprised of 7 different wargames – Amateria, Apfel (currently offline), Blackbox, Blowfish, CTF (currently offline), Logic and Tux. Every wargame has a variety of challenges ranging from standard vulnerabilities to reverse engineering challenges.
7. MICROCORRUPTIONMicrocorruption is an embedded security CTF where you have to reverse engineer fictional Lockitall electronic lock devices. The Lockitall devices secure the bearer bounds housed in warehouses owned by the also fictional Cy Yombinator company. Along the way you’ll learn some assembly, how to use a debugger, how to single step the lock code, set breakpoints, and examine memory all in an attempt to steal the bearer bonds from the warehouses.
8. REVERSING.KRreversing.kr has 26 challenges to test your cracking and reverse engineering abilities. The site hasn’t been updated since the end of 2012, but the challenges available are still valuable learning resources.
10. W3CHALLSW3Challs is a pentesting training platform with numerous challenges across different categories including Hacking, Cracking, Wargames, Forensic, Cryptography, Steganography and Programming. The aim of the platform is to provide realistic challenges, not simulations and points are awarded based on the difficulty of the challenge (easy, medium, hard). There’s a forum where you can discuss and walkthrough the challenges with other members.
12. EXPLOIT EXERCISESExploit Exercises provides a variety of virtual machines, documentation and challenges that can be used to learn about a variety of computer security issues such as privilege escalation, vulnerability analysis, exploit development, debugging, reverse engineering, and general cyber security issues.
13. RINGZER0 TEAM ONLINE CTFRingZer0 Team Online CTF offers a ton of challenges, 234 as of this post, that will test your hacking skills across multiple categories including Cryptography, Jail Escaping, Malware Analysis, SQL Injection, Shellcoding and more. After you successfully complete a challenge, you can write up your solution and submit it to the RingZer0 Team. If your write up is accepted, you’ll earn RingZer0Gold which can be exchanged for hints during future challenges.
14. HELLBOUND HACKERSHellbound Hackers offers traditional exploit challenges, but they also offer some challenges that others don’t such as web and app patching and timed challenges. The web and app patching challenges have you evaluating a small snippet of code, identifying the exploitable line of code and suggesting a the code to patch it. The timed challenges have the extra constraint of solving the challenge in a set amount of time. I thought these two categories were a cool differentiator from most other CTF sites.
15. TRY2HACKTry2Hack provides several security oriented challenges for your entertainment and is one of the oldest challenge sites still around. The challenges are diverse and get progressively harder.
16. HACK.MEHack.me is a large collection of vulnerable web apps for practicing your offensive hacking skills. All vulnerable web apps are contributed by the community and each one can be run on the fly in a safe, isolated sandbox.
17. HACKTHIS!!HackThis!! is comprised of 50+ hacking levels with each worth a set number of points depending on its difficulty level. Similar to Hack This Site, HackThis!! also features a lively community, numerous hacking related articles and news, and a forum where you can discuss the levels and a security related topics that might be of interest to you.
18. ENIGMA GROUPEnigma Group has over 300 challenges with a focus on the OWASP Top 10 exploits. They boast nearly 48,000 active members and host weekly CTF challenges as well as weekly and monthly contests.
19. GOOGLE GRUYEREGoogle Gruyere shows how web application vulnerabilities can be exploited and how to defend against these attacks. You’ll get a chance to do some real penetration testing and actually exploit a real application with attacks like XSS and XSRF.
20. GAME OF HACKSGame of Hacks presents you with a series of code snippets, multiple choice quiz style, and you must identify the correct vulnerability in the code. While it’s not nearly as in depth as the others on this list, it’s a nice game for identifying vulnerabilities within source code.
21. ROOT MERoot Me hosts over 200 hacking challenges and 50 virtual environments allowing you to practice your hacking skills across a variety of scenarios. It’s definitely one of the best sites on this list.
22. CTFTIMEWhile CTFtime is not a hacking site like the others on this list, it is great resource to stay up to date on CTF events happening around the globe. So if you’re interested in joining a CTF team or participating in an event, then this is the resource for you.