Hey guys! Ready to dive into a super fun and challenging CTF adventure? Today, we’re tackling the "Apple Crumble" box, focusing on exploiting a pfSense firewall. This box is awesome for sharpening your OSCP skills. We'll walk through the entire process, from initial recon to root access, so buckle up and get ready to learn!

Initial Reconnaissance: Setting the Stage

Okay, so the first thing we need to do is get our bearings. Initial reconnaissance is absolutely critical in any CTF challenge, and this one is no different. Reconnaissance helps us understand our target environment. We need to figure out what services are running, what ports are open, and generally map out the attack surface. We start with the basics. Usually, I kick things off with nmap. Nmap is a network scanner that lets you discover hosts and services on a computer network, thus creating an inventory. It's like our digital detective, sniffing around to gather clues. A basic SYN scan (using the -sS flag) is usually my go-to. This type of scan is stealthy and efficient, quickly identifying open ports without completing the full TCP handshake. We can enhance this with version detection (-sV) to determine the software versions running on those ports and OS detection (-O) to guess which operating system the target is running. Another useful flag is -p-, which tells Nmap to scan all 65535 ports. This ensures we don't miss anything lurking on less common ports. So, the command would look something like this:

nmap -sS -sV -O -p- <target_ip>

Once the scan completes, we carefully examine the output. Look for any unusual ports or services. Common ports like 80 (HTTP), 443 (HTTPS), 22 (SSH), and 21 (FTP) are always worth investigating. But don't ignore the less common ones! They might be running custom applications or services with known vulnerabilities. In this case, let's say the Nmap scan reveals a pfSense firewall running on the target machine. This is a goldmine! pfSense is an open-source firewall distribution based on FreeBSD, and it's widely used. Knowing this immediately narrows our focus. We now know what we're dealing with and can start looking for pfSense-specific vulnerabilities. We also need to pay attention to any other services running behind the firewall. Are there any web servers, databases, or other applications exposed? These could be potential entry points as well. Take detailed notes on everything you find during this phase. The more information you gather, the better equipped you'll be to plan your attack. Remember, reconnaissance is not just about running a single Nmap scan. It's an iterative process. As you learn more about the target, you may need to run additional scans with different options to gather more specific information. Keep digging until you have a solid understanding of the target environment. With a clear picture of the attack surface, we can move on to the next phase: vulnerability analysis.

Vulnerability Analysis: Finding the Cracks

Alright, now that we've mapped out our target, the next step is to find some weaknesses, right? Vulnerability analysis is all about identifying potential entry points we can exploit. Since we've discovered a pfSense firewall, that’s where we’ll start. We're going to use a combination of manual research and automated tools to uncover any known vulnerabilities. First things first, let’s hit up the usual suspects: Exploit-DB, CVE databases, and Metasploit. These are treasure troves of information about known vulnerabilities and exploits. We'll search for pfSense-specific exploits, paying close attention to the version number we identified during our Nmap scan. Version numbers are super important because exploits are often specific to certain versions of software. A vulnerability that exists in one version may be patched in another, so we need to make sure we're targeting the right version. We might find Remote Code Execution (RCE) vulnerabilities. RCE vulns are critical. They allow us to execute arbitrary code on the target machine, effectively giving us control. Keep an eye out for SQL injection vulnerabilities. If the pfSense firewall has a web-based interface (which it probably does), it might be vulnerable to SQL injection. This would allow us to bypass authentication and gain access to the system. Cross-Site Scripting (XSS) vulnerabilities can also be useful. While they might not directly lead to root access, they can be used to steal credentials or launch other attacks. We can use tools like Nessus or OpenVAS. These are vulnerability scanners that can automatically identify known vulnerabilities in a system. They work by comparing the software versions and configurations of the target machine against a database of known vulnerabilities. These scanners can generate detailed reports that highlight potential weaknesses and provide recommendations for remediation. They can be noisy and resource-intensive, so use them with caution. Make sure you have permission to scan the target machine before running a vulnerability scanner. Never blindly trust the output of automated tools. Always verify the results manually. False positives are common, so you need to confirm that the vulnerability actually exists before attempting to exploit it. We can manually analyze the pfSense configuration files. These files contain sensitive information about the firewall's configuration, such as usernames, passwords, and network settings. If we can access these files (either through a vulnerability or by guessing default credentials), we might be able to find a way to compromise the system. Remember, vulnerability analysis is a process of elimination. We're looking for the weakest link in the chain. By systematically investigating each potential vulnerability, we can narrow down our focus and identify the most promising attack vectors. Once we've identified a vulnerability that we think we can exploit, it's time to move on to the next phase: exploitation.

Exploitation: Pwning the Box

Time to get our hands dirty! Exploitation is where we put our research to the test and try to gain access to the system. Let's say, after our vulnerability analysis, we found a Remote Code Execution (RCE) vulnerability in the pfSense web interface. This is fantastic news because RCE vulnerabilities allow us to execute arbitrary code on the target machine. Now we need to craft an exploit. We can use Metasploit. Metasploit is a powerful exploitation framework that provides a wide range of tools and modules for exploiting vulnerabilities. It has a large database of exploits for various software and operating systems, including pfSense. Search for a relevant module in Metasploit and configure it with the target IP address and any other required parameters. A custom exploit can be created using Python or Ruby. We'll need to understand the technical details of the vulnerability. This might involve reverse engineering the vulnerable code or analyzing network traffic to understand how the exploit works. Payloads are the code that we want to execute on the target machine. They can range from simple commands to full-fledged reverse shells. Choose a payload that is appropriate for the vulnerability and the target environment. Reverse shells are a great way to gain persistent access to the target machine. They establish a connection from the target back to our attacking machine, allowing us to execute commands and interact with the system. Once we've crafted our exploit and payload, it's time to launch the attack. We carefully monitor the results to see if the exploit is successful. If everything goes according to plan, we should get a shell on the target machine. We'll check the privileges of the user account that we've gained access to. If we're lucky, we might already have root privileges. But if not, we'll need to escalate our privileges. Privilege escalation is the process of gaining higher-level access to the system. This might involve exploiting another vulnerability or misconfiguration. Once we have root access, we've effectively pwned the box. We can now access any file on the system, install software, and make changes to the configuration. We'll create a backdoor. A backdoor is a way to regain access to the system in the future, even if the original vulnerability is patched. This might involve creating a new user account with administrative privileges or installing a persistent reverse shell. This is just an example, and the exact steps will vary depending on the vulnerability and the target environment. The key is to be persistent, creative, and adaptable. Don't be afraid to try different approaches and learn from your mistakes. Remember, exploitation is a skill that takes time and practice to develop. The more you do it, the better you'll become. With each successful exploit, you'll gain a deeper understanding of how systems work and how to break them.

Privilege Escalation: Becoming Root

So, we've got a shell, but we’re not root yet. Time to level up! Privilege escalation is the art of going from a low-privileged user to the ultimate boss: root. This often involves finding vulnerabilities or misconfigurations that allow us to gain higher-level access to the system. Let's enumerate the system. We need to gather as much information as possible about the system's configuration and running processes. This will help us identify potential privilege escalation vectors. Look for SUID/GUID binaries. These are programs that run with the privileges of the owner or group, regardless of who executes them. If a SUID/GUID binary has a vulnerability or is misconfigured, it can be used to gain elevated privileges. Check for kernel exploits. The kernel is the core of the operating system, and vulnerabilities in the kernel can often be exploited to gain root access. Look for publicly available kernel exploits that are applicable to the target system. Investigate cron jobs. Cron jobs are scheduled tasks that run automatically. If a cron job is running with elevated privileges, and we can modify the script that it executes, we can use it to gain root access. Examine world-writable files. If a file is writable by all users, it might be possible to overwrite it with malicious code and then execute it with elevated privileges. Search for misconfigured services. Services that are running with elevated privileges might have vulnerabilities or misconfigurations that can be exploited to gain root access. Consider exploiting weak file permissions. Incorrect file permissions can sometimes allow unauthorized users to read sensitive data or execute arbitrary code. For example, if a configuration file containing passwords has world-readable permissions, it could be used to gain privileged access. Another step we can take is to exploit PATH vulnerabilities. The PATH environment variable specifies the directories that the system searches for executable files. If a directory in the PATH is writable by a non-privileged user, it might be possible to create a malicious executable with the same name as a system command, and then trick the system into executing our malicious code. Also, we need to use tools like linenum.sh or Linux Exploit Suggester. These scripts automate the process of enumerating the system and identifying potential privilege escalation vulnerabilities. They can save us a lot of time and effort, but it's important to understand how they work and verify their results manually. Kernel exploits are a classic way to escalate privileges. If we can find a kernel exploit that is applicable to the target system, it can be a quick and easy way to gain root access. However, kernel exploits can be difficult to find and exploit, and they can sometimes crash the system. We also need to exploit SUID binaries. These are executables that run with the privileges of their owner. If a SUID binary has a vulnerability, it can be used to gain elevated privileges. We can use the find command to search for SUID binaries on the system. We should be creative and think outside the box. Privilege escalation is often a process of trial and error, so we need to be persistent and try different approaches until we find something that works. Remember, the key to successful privilege escalation is to gather as much information as possible about the system and then use that information to identify potential vulnerabilities or misconfigurations that can be exploited to gain root access. Once we've gained root access, we've effectively pwned the box. We can now access any file on the system, install software, and make changes to the configuration.

Post-Exploitation: Covering Your Tracks

Alright, we're root! But we're not done yet. Post-exploitation is about solidifying our access, maintaining persistence, and cleaning up any evidence of our presence. First thing's first: let's grab those juicy credentials! Look for password files, API keys, and any other sensitive information that we can use to further our access to the network. We can search for interesting files using commands like grep and find. Backdoors are a must. We don't want to have to go through all that hard work again if we lose our initial access. Set up a persistent backdoor using SSH keys, cron jobs, or a web shell. Ensure the backdoor is well hidden and difficult to detect. If the box is part of a larger network, we can use it as a pivot point to attack other systems. Use tools like sshuttle or chisel to create a tunnel through the compromised box and access internal networks. We can collect system logs, bash history, and other files that might contain information about our activities. Edit or delete these files to remove any evidence of our presence. We can use tools like shred to securely delete files and overwrite disk space to prevent data recovery. Rootkits are advanced tools that can be used to hide our presence on the system. They typically replace system binaries with modified versions that hide our processes, files, and network connections. However, rootkits can be difficult to install and maintain, and they can sometimes cause system instability. We can document everything we did during the engagement, from the initial reconnaissance to the post-exploitation phase. This documentation will be valuable for future reference and for sharing our findings with others. After covering our tracks, we should leave the system in a stable state. Avoid making any changes that could cause the system to crash or become unusable. Reboot the system if necessary to ensure that our changes are properly applied. Remember, the goal of post-exploitation is to maintain access to the system while minimizing the risk of detection. By following these steps, we can ensure that we can return to the system at any time and that our activities remain undetected. Also, it is important to remember to respect the law and only perform these activities on systems that we have permission to access. Unauthorized access to computer systems is illegal and can have serious consequences. Be ethical and responsible in our cybersecurity activities. Always obtain proper authorization before conducting penetration tests or other security assessments. We have successfully compromised the Apple Crumble box! We've gone from initial reconnaissance to root access, and we've learned a lot along the way. This exercise has helped us sharpen our OSCP skills and gain a deeper understanding of penetration testing techniques.

Conclusion: Lessons Learned

Alright guys, that wraps up our adventure into the Apple Crumble box and its pfSense firewall! We’ve covered everything from initial recon to post-exploitation, picking up some serious skills along the way. What did we learn? First, reconnaissance is king. A thorough understanding of your target is essential for a successful attack. Don’t rush this step. Vulnerability analysis is a constant game of cat and mouse. Stay updated on the latest vulnerabilities and learn how to identify them quickly. Exploitation requires creativity and persistence. Don't be afraid to try different approaches and adapt to the situation. Privilege escalation is a critical skill. Learn how to identify and exploit common privilege escalation vectors. Post-exploitation is about maintaining access and covering our tracks. Don't forget to clean up after yourself and leave the system in a stable state. More than anything, these CTFs teach you to think outside the box and constantly learn. The field of cybersecurity is always evolving, so it's important to stay up-to-date on the latest trends and techniques. Practice, practice, practice! The more you do these kinds of exercises, the better you'll become at penetration testing. So, keep hacking, keep learning, and keep pushing yourself to improve. And remember, always use your powers for good! Happy hacking, and I'll catch you in the next CTF walkthrough!