Hello friends! Today we are going to take another CTF challenge known as thewall. The credit for making this vm machine goes to “Xerubus” and it is another boot2root challenge where we have to root the VM to complete the challenge. You can download this VM here.
Let us start form getting to know the IP of VM (Here, I have it at 192.168.0.17 but you will have to find your own)
We did a nmap scan but it showed nothing. So we use arp to check if it is broadcasting anything.
We found that it is broadcasting something on the network, so we use wireshark to check at which port it is broadcasting the data.
We found that it is broadcasting something at port 1337 so we use netcat to listen at port 1337.
nc –lvp 1337
We found it was broadcasting something related to pink Floyd, we again do a nmap scan to check if it affected anything.
nmap -sV 192.168.0.17
As we can see that port 80 is open, so we open this ip in our browser.
We take a look at the source code of the browser and find a hexadecimal encoded string.
When we decode it we find a md5 encoded string and hint to do stegnography.
We decode the md5 encoded string and found a string called divisionbell.
We download the image from the webpage and using steghide we check if something is hidden behind the image. When try to extract information it prompts for password using the string we decoded above we are able to find that a text file is hidden behind the image and are able to extract it.
steghide –info pink_floyd.jpg
steghide extract –sf pink_floyd.jpg
When we open the text file we find a base64 encoded string and md5 encoded string and a hint to use it at port 1965.
First we decode the base64 encoded string and found the string SydBarret.
Then we decode the md5 encoded string and found the string pinkfloydrocks.
Port enumeration on 1965 shows it is running openssh, we check if we can login using this as username:SydBarret and password:pinkfloydrocks.
When we try to login it shows us that we can only connect through sftp. So we use SydBarrett as username and pinkfloydrocks as password to login through sftp.
Now that we are inside, we find a file called eclipsed_by_the_moon, we download it to our system.
We check what kind of file it is, we find that it is a zip file, we extract it using tar.
tar xvfz eclipsed_by_the_moon
After extracting the file, we check what kind of file it is and find that it is a boot sector.
We check if we can recover any file inside the boot sector using testdisk.
We select the image to recover files from.
We select none portioned media as it is a boot sector.
We go to advanced to recover file from the image.
We then select the partition in which we want to extract the file from and select undelete to recover the files.
We find that an image file is recovered, we copy it.
We select the directory of our system in which we want to copy the file.
We check the image we just recovered and find the picture of Roger Waters, we also got a password inside the image.
We login trough ssh, enumerating the username we find that RogerWaters is the username and password is hello_is_there_anybody_in_there.
After getting in, we find that there are different directory for different users of pink floyd band members.
We also find that we have limited access and cannot access their directories so we check for binaries available to other users and find that user NickMason and DavidGilmour have binaries called brick and shineon available to them.
find / -user DavidGilmour 2>/dev/null
find / -user NickMason 2>/dev/null
We don’t have access to run the binary shineon but when we run brick it asks us a question. When we answer it correctly we become the user NickMason.
Now we can access the directory NickMason/. We find an image file inside we use scp to send it to our local system.
scp nick_mason_profile_pic.jpg [email protected]:/root/Desktop
We check the file type and find that it is an audio file. We change the file from .jpg to .ogg.
When we listen to the audio, we find that morse code is also playing in the background along with the music. We cut the frequency of the audio to retrieve the morse code.
.-. .. -.-. …. .- .-. -.. .– .-. .. –. …. – .—- —-. ….- …– ..-. .. … .-
We find that the morse code translates to richardwright1943farfisa. We use RichardWright as username and 1943farfisa as password to login as user RichardWright.
Now we try to run the binary shineon, after running the binary we find that we can change the folder with symbolic link from DavidGilmour to RichardWright.
ln –s /bin/ksh /tmp/mail
When we now run the shineon we become user DavidGilmour.
Inside DavidGilmour/ folder we find a link inside the file.
When we open this link on the browser we find an image on which something is written.
When we decrease the contrast of the image, we find a hexadecimal string.
Then we also send an image file that we find inside the DavidGilmour/ folder using scp.
scp david_gilmour_profile_pic.jpg [email protected]:/root/Desktop/
We check for strings inside the image file and found string who_are_you_and_who_am_i.
Now we use DavidGilmour as username and who_are_you_and_who_am_i as password.
We now are in welcometothemachine group; we move inside /var/www/htdocs/welcometothemachine/.
We find a file called PinkFloyd, we run the file and find it asks a question. We use the hexadecimal string inside the image we find on the webpage.
Now we are given the permission to get root, as DavidGilmour is added into sudoers after running this program.
Now when we enter root/ directory and we find the flag stating the end of the VM challenge.
Author: Sayantan Bera is a technical writer at hacking articles and cyber security enthusiast. Contact Here