In this post, I would like to share a walkthrough of the Secret Machine from HackTheBox

This room is been considered difficulty rated as an Easy machine on HackThebox

Source: Secret’s Machine icon on HackTheBox

What you will gain from Secret machine?

For the user flag, you will download a token_secret from the files on the website. We were also required to play jwt code with the token secret and execute a shell from BurpSuite

As for the root flag, you need to find a program on the machine where we are required to crash the program so that we can obtain the root flag

Information Gathering on Secret Machine

Once we have started the VPN connection which requires download from Hackthebox, we can start information gathering on the machine by executing the command nmap -sC -sV -p- <IP Address> -PN 

Let’s access the website interface to find any vulnerability that we can exploit

Sadly, we didn’t find anything to exploit on the website interface except there’s the documentation for registering and login users. It might be useful later on.

From the Nmap result, I notice there’s a port 3000/tcp open which it has installed with Node.js (Express middleware)

Enumerate directory using gobuster

Let’s enumerate for any interesting directory on the machine by using gobuster

The output above appear from a normal enumeration using port 80 and the same output show when i enumerate using port 3000

There have two interesting that caught my attention such as

  • /api
  • /download

Let’s dig deeper on the /api/ directory which leads us to find another directory such as /users. From this point, i have been wondering whether there’s a registered directory that we can use over here.

Before that, let’s try to look into /download the directory and who knows if there’s something we can use from that directory.

## Sorry for not being able to provide evidence on the gobuster result for /download/ directory ##

Let’s go download the files that we managed to obtain from the gobuster result.

Therefore, let’s unzip the files which we have successfully downloaded just now and see the content of the folder.

Inside the folder, there are a few files that have been stored which I didn’t see anything interesting.

As a result, let’s see anything that has been hidden from our eyes.

Other files that we can look into is .env and .git therefore let’s dig deeper on the file or folder.

Due to some spacing on the post, I will skip another file except for the file that I need to showcase in this post.

Let’s read the HEAD file which the content will look such as below:

From the file content, I managed that .env have been removed for a security reason

We need to should restore the git commit that has been removed previously by using the command git revert id

Gaining Privileges Acces on Secret Machine

As a result, we can read the .env file which has been removed where we have presented with the token_secret which we will be using in the next step.

The next step that we can do is to register a username on the machine.

Normally, we use a browser or burpsuite to register and login directly but this time, I will make sure of the curl command for this activity.

As a result, we can login to the API using the credentials that we created just now. However, we get a jwt code after we try to login to the API interface.

Let’s decode the jwt code on the website jwt.io where you can see the output similar as shown above.

Right now, we can change the name from darknite to theadmin which we found out from the document earlier.

We are required to put together the content of token_secret over here.

Getting reverse shell connection

Let’s start our nc listener

Let’s execute the curl command to send the shell to the system so that we managed to obtain the reverse shell connection back to us.

For this activity, I use the python reverse shell command to successfully obtain the shell.

## For those who are wondering on the command –proxy http://127.0.0.1:8080 is used for. The purpose to incept the packet using BurpSuite ##

Sadly, our attempt look unsuccessfully to obtain the reverse shell connection.

As a result, I need to use a different type of shell command from Online – Reverse Shell Generator (revshells.com)

I will try using the shell command shown above to get the shell back.

We didn’t get any response from the packet which look promising to obtain a shell.

Voila! We have successfully obtained a reverse shell.

It looks like we access it as dasith privileges.

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

Escalate Root Priviliges on Secret machine

We can run automation tools such as linpeas.sh to find us any interesting file or SUID that we can use for exploitation.

However, I will find the SUID or malicious program manually

There’s no way to get ssh access to the machine via dasith privileges access.

Based on my experience, there should be something interesting to look at on those directories:

  • /opt
  • /etc/
  • /var/

Uwu! There’s something on the /opt/ directory that we can analyze further.

Let’s analyze the code.c file

I notice that there’s a function for coredump generation that have been enabling that we are required to crash some program.

For that purpose, we should be getting another reverse shell whose function such as follows:

  • One Reverse Shell is executing program
  • One Reverse Shell is to kill/crash the program

Getting SSH private key

The screenshot above shows that we can possibly retrieve ssh id_rsa so that we can use it to access the machine via ssh

We can use ps aux command to find PID of the program which in my case is 1543.

So, let’s kill that program by using the command “kill -6 PID

Finally, the program has crashed based on the screenshot above.

Let’s look at the log of the crash at /var/crash directory

Right now, we should be reading the file that contains ssh key.

You will be able to see the SSH key as shown above.

We can give permission to the root_id_rsa

We should be able to access the machine via ssh but sadly we failed.

After a while, i notice my mistake where i should be giving permission chmod 600 root_id_rsa rather than chmod +x root_id_rsa

It should be working now.

Finally, we managed to access the machine as root privileges access via ssh

We should be able to read the root flag by executing “cat root.txt

Another way to get a root flag without ssh access is by changing /root/.ssh/id_rsa to /root/root.txt just shown above.

-THE END-

Happy Learning Guys!

Extra Information

We can go to /etc/shadow so that we can unlock and read the write-up

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