NSE was designed with flexibility in mind, and supports several features to control the execution of NSE scripts. In this chapter, we will learn not only that NSE scripts can be executed during different scan phases but also that they can be selected with a high level of granularity, depending on host conditions. In combination with robust libraries and plenty of configuration options, NSE offers a level of flexibility that is hard to match in other tools and frameworks.

We can begin testing NSE against the host, scanme.nmap.org. This server is managed by the Nmap project and allows users to scan it as long as the scans are not too intrusive. Let's begin by running a scan with version detection and NSE enabled against our test target—scanme.nmap.org:

#nmap –sV –sC -O scanme.nmap.org

You should see something similar to this:

The previous command ran a SYN scan with OS detection (-O), service detection (-sV), and most importantly with NSE on (-sC). The -sC option enables the NSE and runs any script in the default category. This set of scripts is considered safe as it won't perform any operations that could interfere with a service running on the target host. However, note that some of the scripts perform actions that can raise alarms in intrusion detection systems (IDS) and intrusion prevention systems (IPS).

The safe category contains scripts such as these:

The previously mentioned scripts are only a few compared to the current total of almost 500. That's a whole lot more of information that can be collected by simply using NSE.