On getting cracked and recovering with NMAP

Two weeks ago I wrote about stealth scans and promised to follow up with a column on NMAP, Fyodor's wonderful open source port scanner. But between that time and the appearance of this column, two big stories got in the way. First came word that LinuxWorld.com was moving to ITworld.com's site. Then came a rare opportunity to bring together Bob Young and a player from the Dark Side in an exclusive one-on-one, which was presented last week in place of the stealth scan follow-up (see Resources for links). My apologies for being late, but here it is. And just as someone out there is certain to be snickering about my network security skills, better late than never. (See Resources for links to previous columns.)

Call it baud karma. Call it carelessness. Call it inevitable. I was 0wn3d and didn't know it. After downloading and installing BETA 21 of version 2.54 of NMAP (and its graphical frontend), I su'd to root, fired it up, and aimed a FIN stealth scan at ports 1-32000 on my server. I was running portsentry on the server, but my desktop machine -- the one I was running NMAP on -- was on the portsentry ignore list so that it wouldn't simply reroute my inquisitive packets to /dev/null after I hit the first protected port.

The image above shows the way I had NMAP configured for the scan. It took less than a minute to ruin my entire week. The results are below. The same scan produces markedly different results today.

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