Nmap’s New Math? 9 = 8 but does 3,674 = 65,536?

Fyodor’s inclusion of the results from the Top Ports Project into the latest version (4.76) of Nmap is a welcome addition to information security professionals who need to perform port scans of large networks in short periods of time. **cough*** Consulting Firms ***cough**

However, the claim that using the “–top-ports” switch to scan only the top 3,674 TCP ports is 100% effective opens the door for yet another false sense of security. I wholeheartedly believe that it was NOT Fyodor’s intention for organizations to rely solely on port scans using this configuration to determine which ports are open. However, it does not require a leap of faith to believe that some less “offensive minded” security professionals will now use this configuration to get a “complete picture” of their networks.

Why is this a problem? If you are reading this blog, you probably already know where I am going with this. It doesn’t require another leap of faith to believe that an attacker or offensive minded individual would examine the “Top Ports” list and code their malware or configure their tools to operate on ports that are not included in the list. The result? Those who subscribe to this complete picture mentality will not discover the open ports.

So how do we effectively leverage the hard work of the Top Ports Project? I’m not entirely sure yet. Perhaps we use the “–top-ports” switch to perform differential scans and continue to use “-p-” to perform baseline scans? Or maybe we use the “–top-ports” switch to perform discovery scans and “-p-” to perform enumeration?

I do know that the information that has been provided as a result of the Top Ports Project is valuable. How do you think we can effectively use this information?

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