How do I write my own Nmap script?

Writing your own Nmap script involves using the Lua programming language, which is the scripting language used by the Nmap Scripting Engine (NSE). Here’s a step-by-step guide to help you create a simple Nmap script:

Step 1: Set Up Your Environment

1. Install Nmap: Ensure you have Nmap installed on your system.
2. Familiarize with Lua: Basic knowledge of Lua will help you write scripts effectively. You can find resources online to learn Lua.

Step 2: Create Your Script File

1. Create a New File: Use a text editor to create a new file with a .nse extension. For example, my_script.nse.

Step 3: Write the Script

Here’s a simple example of an Nmap script that checks if a web server is running on a specified port:

description = [[
  A simple script to check if a web server is running.
]]

---
-- @usage
-- nmap -p 80 --script my_script
-- 
-- @output
-- PORT   STATE SERVICE
-- 80/tcp open  http
-- 
-- @args port The port to check (default is 80).
--

local port = 80

action = function(host, port)
  local socket = nmap.new_socket()
  socket:set_timeout(5000)

  local status, err = socket:connect(host.ip, port)
  if status then
    return "Web server is running on port " .. port
  else
    return "No web server found on port " .. port
  end
end

Step 4: Save the Script

Save your script file in the Nmap scripts directory, typically located at /usr/share/nmap/scripts/.

Step 5: Run Your Script

You can run your script using the following command:

nmap --script my_script -p 80 localhost

Step 6: Debugging and Testing

• Debugging: If your script doesn’t work as expected, check the Nmap output for errors. You can also add print statements to help debug.
• Testing: Test your script against different hosts and ports to ensure it behaves as intended.

Conclusion

Creating your own Nmap script allows you to extend its functionality for specific tasks. Start with simple scripts and gradually incorporate more complex logic as you become comfortable with Lua and the Nmap scripting framework.

If you have any questions or need further assistance, feel free to ask!