NMAP is a powerful network mapping and security auditing tool. It provides a way to scan and gather information about hosts, ports, and services on a network. However, the capabilities of NMAP go beyond the basic scanning features. One of the most significant features of NMAP is its scripting engine. The scripting engine allows users to write scripts to automate various tasks, such as service detection, host enumeration, and vulnerability scanning. In this article, we will be discussing NMAP scripts and how they work.

What are NMAP Scripts?

NMAP scripts are essentially small pieces of code written in the Lua programming language that automate specific tasks. These scripts can be used to gather information about hosts, services, and vulnerabilities on a network. They can also be used to automate routine tasks, such as checking for open ports and gathering information about the operating system running on a host.

The NMAP scripting engine is a powerful feature that makes it possible to automate tasks that would otherwise require a lot of manual effort. For example, you could write a script to check for open ports on a host and automatically send an alert if a specific port is found open. This type of automation can save a significant amount of time and effort, especially when dealing with large networks.

How to Write NMAP Scripts

NMAP scripts are written in the Lua programming language. Lua is a lightweight, fast, and efficient scripting language that is designed to be easy to learn and use. If you are familiar with other scripting languages such as Python or Perl, you should have no problem learning Lua and writing NMAP scripts.

When writing NMAP scripts, you need to be familiar with the NMAP scripting engine API (Application Programming Interface). The API provides access to a wide range of information, including the results of scans, the state of the network, and various other information that can be used to automate tasks.

For example, you might write a script to check for open ports on a host and return a list of open ports. You would use the API to access the results of the scan, extract the list of open ports, and return this information to the user.

NMAP Scripts in Action

To see how NMAP scripts work in practice, let’s look at a few examples.

Service Detection

One of the most common tasks performed with NMAP is service detection. Service detection involves checking for open ports on a host and identifying the type of service running on each port. This information is used to understand the security posture of a network, as well as to plan for network upgrades or patches.

A script to automate service detection might look something like this:

-- Check for open ports and identify the type of service running on each port

local open_ports = {}

for i, port in ipairs(host.get_ports(host)) do
  if port.is_open then
    table.insert(open_ports, port.number)
  end
end

return "Open Ports: " .. table.concat(open_ports, ",")

In this example, the script uses the NMAP API to access the results of a scan and extract the list of open ports. The script then returns this information to the user.

Host Enumeration

Another common task performed with NMAP is host enumeration. Host enumeration involves identifying the number of hosts on a network and the type of operating system running on each host. This information is used to understand the security posture of a network, as well as to plan for network upgrades or patches.

A script to automate host enumeration might look something like this:

-- Enumerate all hosts on the network and identify the operating system running on each host

local host_list = {}

for i, host in ipairs(nmap.get_hosts()) do
  local os = host.os_fingerprint
  table.insert(host_list, host.ip .. " (" .. (os and os.osclass[1].osfamily or "Unknown") .. ")")
end

return "Hosts: " .. table.concat(host_list, "\n")

In this example, the script uses the NMAP API to access the results of a scan and extract the list of hosts on the network. The script then returns this information to the user.

Vulnerability Scanning

NMAP scripts can also be used to automate vulnerability scanning. Vulnerability scanning involves checking for known vulnerabilities on a network and reporting any that are found. This information is used to understand the security posture of a network, as well as to plan for network upgrades or patches.

A script to automate vulnerability scanning might look something like this:

-- Scan for known vulnerabilities and report any that are found

local vulnerabilities = {}

for i, host in ipairs(nmap.get_hosts()) do
  for j, script in ipairs(host.get_scripts(host)) do
    if string.find(script.output, "VULNERABLE") then
      table.insert(vulnerabilities, host.ip .. ": " .. script.output)
    end
  end
end

return "Vulnerabilities: " .. table.concat(vulnerabilities, "\n")

In this example, the script uses the NMAP API to access the results of a scan and extract any vulnerabilities that were found. The script then returns this information to the user.

Using NMAP Scripts

NMAP scripts are executed from the command line using the following syntax:

nmap -sC [hosts or network]

The -sC option tells NMAP to use the default set of scripts. If you want to run a specific script, you can use the -script option:

nmap -script=[script name] [hosts or network]

For example, if you wanted to run the vulnerability scanning script we looked at earlier, you would use the following command:

nmap -script=vulnerability-scan [hosts or network]

Conclusion

NMAP scripts are an incredibly powerful feature that allow users to automate various tasks, such as service detection, host enumeration, and vulnerability scanning. Whether you’re a network administrator or a security professional, the ability to automate routine tasks can save a significant amount of time and effort. If you’re familiar with programming, writing NMAP scripts is a breeze, and if you’re not, there are plenty of pre-written scripts available that you can use to get started.