Ok so to be clear when I said team I mean a bunch of college students preparing for different ctfs, but these are some of the more helpful resources we have found:

Tryhackme: personal favorite especially for beginners Hackthebox: great for learning/practicing attacks Overthewire: another good ctf site

We try to build many of our own ctf like machines, then each person switches their machine with another person and the other person tries to secure the vulnerabilities without knowing anything about the machine. Once everyone has secured their machines we try to attack them using the notes made while setting them up. This is our step by step for that process.

1. download an old version of a distro. (Ubuntu 14, deb 9, ect)
2. install and setup the VM without any updates or changes to the default configuration
3. google the distro version (Ubuntu 14.04) + vulnerabilities or exploits
4. read through the different sites to find applications that had huge security issues on that version and begin installing some of the programs that have known exploits

So for example with Ubuntu 14.04 we know there are some Linux kernel exploits.

A quick Google search returned this exploit: https://www.exploit-db.com/exploits/43418

Using Ubuntu's website I looked up other critical vulnerabilities and found these: https://ubuntu.com/security/cves?q=&package=&priority=critical&version=trusty&status=

From here I could add some of the packages mentioned as having exploits and then attempt to exploit them. I could also check newer versions of Ubuntu like 16 to find vulnerabilities that would also apply to older versions.

There is also Mitre's list(s) of the most dangerous software vulnerabilities. They have one for 2023, but also a catalog of lists from previous years.

https://cwe.mitre.org/top25/archive/2023/2023_top25_list.html

Hopefully this helps!