In this post, I would like to share a walkthrough of the Registrytwo Machine from Hack the Box

This room will be considered an Insane machine on Hack the Box

What will you gain from the Registrytwo machine?

For the user flag, you will need to utilize a Docker Registry and authentication server, I will access an image to uncover a Java War file responsible for running the webserver. Through meticulous enumeration and reverse engineering, I will identify various vulnerabilities, including issues with nginx/Tomcat, mass assignment vulnerabilities, and opportunities for session manipulation. These vulnerabilities will be exploited in tandem to establish a foothold within the production container environment. Subsequently, I will craft a rogue Java RMI client to glean file listings and access files on the host system, leveraging discovered credentials to obtain a shell.

As for the root flag, you need to strategically await the restart of the RMI server, promptly initiating a rogue server to seize control of the port before it is reassigned

For those who want to learn or improve CyberSecurity skills especially Red Teaming and Blue Team, You can use the link to support me

Academy link can be found

Information Gathering on Registrytwo Machine

Once we have started the VPN connection which requires a download from Hackthebox, we can start

└──╼ $nmap -sC -sV -oA initial 
Starting Nmap 7.93 ( ) at 2023-07-25 09:02 EST
Nmap scan report for
Host is up (0.015s latency).
Not shown: 996 filtered tcp ports (no-response)
22/tcp   open  ssh                OpenSSH 7.6p1 Ubuntu 4ubuntu0.7 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey: 
|   2048 fab003987e60c2f3118227a135779fd3 (RSA)
|   256 f25906dc33b09fa35eb763ff61359dc5 (ECDSA)
|_  256 e3acabea2bd68ef41fb07b050a69a537 (ED25519)
443/tcp  open  ssl/http           nginx 1.14.0 (Ubuntu)
| ssl-cert: Subject: organizationName=free-hosting/stateOrProvinceName=Berlin/countryName=DE
| Not valid before: 2023-02-01T20:19:22
|_Not valid after:  2024-02-01T20:19:22
|_http-server-header: nginx/1.14.0 (Ubuntu)
|_ssl-date: TLS randomness does not represent time
|_http-title: Did not follow redirect to https://www.webhosting.htb/
5000/tcp open  ssl/http           Docker Registry (API: 2.0)
|_http-title: Site doesn't have a title.
| ssl-cert: Subject: commonName=*.webhosting.htb/organizationName=Acme, Inc./stateOrProvinceName=GD/countryName=CN
| Subject Alternative Name: DNS:webhosting.htb, DNS:webhosting.htb
| Not valid before: 2023-03-26T21:32:06
|_Not valid after:  2024-03-25T21:32:06
5001/tcp open  ssl/commplex-link?
| tls-alpn: 
|   h2
|_  http/1.1
| fingerprint-strings: 
|   FourOhFourRequest: 
|     HTTP/1.0 404 Not Found
|     Content-Type: text/plain; charset=utf-8
|     X-Content-Type-Options: nosniff
|     Date: Sat, 03 Feb 2024 14:03:23 GMT
|     Content-Length: 10
|     found
|   GenericLines, Help, Kerberos, LDAPSearchReq, LPDString, RTSPRequest, SSLSessionReq, TLSSessionReq, TerminalServerCookie: 
|     HTTP/1.1 400 Bad Request
|     Content-Type: text/plain; charset=utf-8
|     Connection: close
|     Request
|   GetRequest, HTTPOptions: 
|     HTTP/1.0 200 OK
|     Content-Type: text/html; charset=utf-8
|     Date: Sat, 03 Feb 2024 14:02:57 GMT
|     Content-Length: 26
|_    <h1>Acme auth server</h1>
| ssl-cert: Subject: commonName=*.webhosting.htb/organizationName=Acme, Inc./stateOrProvinceName=GD/countryName=CN
| Subject Alternative Name: DNS:webhosting.htb, DNS:webhosting.htb
| Not valid before: 2023-03-26T21:32:06
|_Not valid after:  2024-03-25T21:32:06
|_ssl-date: TLS randomness does not represent time
1 service unrecognized despite returning data. If you know the service/version, please submit the following fingerprint at :
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

Service detection performed. Please report any incorrect results at .
Nmap done: 1 IP address (1 host up) scanned in 118.17 seconds
└──╼ $

Let’s access the website interface

Sadly, the website interface with port 80 or 443 finds a dead-end.

However, it gives us a blank website interface when we access the page with port 5000

We managed to sight a page message saying “Acme Auth Server” when accessing the port 5001

During that time, we didn’t retrieve any response when trying to access the page

Enumerating using a manual method

As a result, let’s try a manual method using the curl command

At last, we managed to found a message as show in the screenshot above.

After a while, we also successfully retrieve the token which we can use in our next attempt on the website.

When we tried to access the page by adding some Authorization token, we found a potential directory or path that we could investigate further.

However, we have again obtain a new token when trying to access the repositories.

Boom! We have some sum or information that we can use for further stages.

Therefore, let’s download all the information into one file

Tomcat Enumeration

After a while, we managed to access the webhosting.htb page which leads to the login page.

Let’s create a new account for us to access the dashboard.

The dashboard interface looks like something as shown above.

Let’s try to create a new domain for us to play further

However, nothing that look interesting at this point

We found an Apache Tomcat Example page as shown above. At this stage, we will be using the method can be read here

A screenshot of a computer

Description automatically generated

It looks like a simple Tomcat page.

A screenshot of a computer

Description automatically generated

Let’s access the SessionExample and submit a query which in this case, we will be adding data as “s_IsLoggedInUserRoleManger” to “true

The output will shown in the screenshot above.

A screenshot of a computer

Description automatically generated

We can try to reconfigure the hosting by clicking the “Save Changes” button

Let’s try to insert our bash shell command on a simple file

We also required to start our python server

A screenshot of a computer program

Description automatically generated
A screenshot of a computer program

Description automatically generated

Therefore, let’s try to poison the website by adding the syntax as &<IP Addr>%00.htb after the domains.start-template syntax

Before we can trigger the payload on the website, let’s start our listener.

A black screen with green text

Description automatically generated

Fast forward, we should be getting the output as shown in the screenshot above after we refresh the hosting page.

Ysoserial exploitation of the server

We can use the ysoserial script to upload the file that contains the bash shell into our victim’s machine and execute it.

The command to upload and execute can be seen in the screenshot above.

A computer screen with green text

Description automatically generated

We managed to upload the file into our victim’s

Finally, we managed to retrieve the shell connection on our machine.

Docker Escape to User Access

Sadly, we are inside the docker environment.

We should be transferring the Java script into the victim’s machine. The source code can be found here

We should obtain the credentials for the user like the below:

bash-4.4$ java -jar ExploitRMI.jar eaa4eff1626e cat /home/developer/.git-credentials

At last, we managed to access the machine via SSH service using the credentials that we found earlier.

We can read the user flag by typing the “cat user.txt” command

Escalate to Root Privileges Access on Registrytwo machine

As usual, we can try to see the process within the machine by entering the command “ps aux

There is one process that caught my attention which looks like a Java file being executed.

Let’s investigate further on the directory

We need to enumerate the credentials which leads me to create a bash file to execute it on the machine.

Therefore, let’s download the Registry.jar which i modify from the docker grabber process.

We are required to start some proxy to catch the file that contains the root’s credentials on the registrytwo machine

Once we have started our proxy, we can execute the bash file

We can change to root with the credentials that we found after a long wait.

We can read the root flag by typing the “cat root.txt” command