Easily Check Open Ports for Reverse Shells

In this article, I’ll introduce you to a simple and efficient Bash script I wrote, that uses the built-in /dev/tcp descriptor to test outbound TCP connectivity. This script is dependency-free, easy to use, and perfect for Linux users who want a straightforward way to verify port accessibility for Linux reverse shells.

When troubleshooting network issues or validating firewall configurations, one of the most common challenges is checking if outbound TCP connectivity is open to specific ports. Whether you’re trying to make a reverse shell work, debugging firewall rules, having a quick, lightweight solution at hand is crucial. That’s where my Bash script to check outbound ports comes in.

Outbound port testing is vital for a variety of reasons:

• Debugging Firewall Rules: Ensure that outbound traffic to specific ports is not being blocked.
• Verifying Network Access: Confirm connectivity to external services, like a Kali listener, databases, or web servers.
• Lightweight and Quick Diagnostics: Avoid installing heavy tools like nmap or netcat.

This script leverages the /dev/tcp descriptor, a built-in feature in Bash that allows you to open a TCP connection to a specific host and port. By checking the response, the script determines whether the port is…