TL;DR

We find open 23 port for telnet, and login with root user without password.

Recon

First, we connect to our openvpn using the command, when we use the ovpn file we downloaded for this purpose:

sudo openvpn Downloads/starting_point_agonen.ovpn

Then, we scan the ip using nmap, we’ll run this command:

nmap -sCV -p- --min-rate=10000 10.129.63.138

as we can see, there is an open telnet port:

23/tcp open  telnet  Linux telnetd
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

Login with user root to telnet

we try to connect via telnet:

telnet 10.129.63.138

And it asks for username and password, we try to give several common creds:

Administartor
Admin
root

and luckily, the root user worked without requiring password!

Now, all left is to read flag.txt

Flag:b40abdfe23665f766f9c61ecba8a4c19