I am using Windows 7 host machine and I have loaded a vulnhub ctf into virtualbox. Now i dont have credentials to login to the ctf machine which is a unix machine. Can i get the ipaddress of this CTF Unix machine that i loaded using virtual box. Currently the CTF screen stopped at login prompt.
As Steffen Ullrich said on comments, there is not so much related to security here. Ok, you are trying to do a CTF... but that's all. Anyway before the probably migration of the question I'll try to give you some hints.
First you must determine if your virtual machine is running in NAT mode or in bridged mode. You can check it under configuration-networking options for that machine on Virtualbox.
If is in bridged mode, the virtual machine is going to be on same network as your host machine. Probably it will take an ip from DHCP if you have one configured which is the standard. If bridged is your case, suppose that your home network range is
192.168.0.0/24. Use nmap to scan your network in order to find your vm. A command like this usually is enough (a standard connect scan generating a lot of noise):
nmap -sT 192.168.0.0/24
Remember to change your network range on command if is different.
If your vm is in NAT mode. There will be a different network range between your host machine and your vm. Usually, the default network range for this on Virtualbox is
10.0.2.0/24 (your host usually is
10.0.2.1 and the first vm should be
10.0.2.15 if everything is normal).
Hope it helps.