The vast majority of log messages go forever unread. Log monitoring tools such as Logwatch and Swatch can certainly help, but the reality is that system logs are only marginally effective at detecting Nmap activity.
Special purpose port scan detectors are a more effective approach to detecting Nmap activity. Two common examples are PortSentry and Scanlogd. Scanlogd has been around since and was carefully designed for security. No vulnerabilities have been reported during its lifetime. PortSentry offers similar features, as well as a reactive capability that blocks the source IP of suspected scanners. Yet the type of administrator who cares enough to keep tabs on port scans will also want to know about more serious attacks such as exploit attempts and installed backdoors.
For this reason, intrusion detection systems that alert on a wide range of suspicious behavior are more popular than these special-purpose tools. Many vendors now sell intrusion detection systems, but Nmap users gravitate to an open-source lightweight IDS named Snort.
In order to increase version detection accuracy, this specific scan integrates NSE Nmap Scripting Engine to launch scripts against suspected services to confirm or discard detections.
You can always regulate the intensity of a scan as will be explained below despite it will be only useful against uncommon services on targets. In some cases, Nmap cannot distinguish filtered ports, in such cases Nmap will mark them as filtered, yet if instructed it will continue probes against these ports. It is possible to determine que grade of intensity Nmap will use to detect software versions, by default the level 7 and the possible range is from 0 to 9.
This feature will only show results if uncommon services are running on the target, there will not be differences in servers with widely used services. Note that the Nmap -A option enables version detection among other things. Thus you can effectively obtain the same info as rpcinfo -p even if the target's portmapper is behind a firewall or protected by TCP wrappers. Decoys do not currently work with RPC scan. When Nmap receives responses from a service but cannot match them to its database, it prints out a special fingerprint and a URL for you to submit it to if you know for sure what is running on the port.
Please take a couple minutes to make the submission so that your find can benefit everyone. Enables version detection, as discussed above.
Alternatively, you can use -A , which enables version detection among other things. Prior to March , it was used to active the RPC grinder separately from version detection, but now these options are always combined. This behavior can be changed by modifying or removing the Exclude directive in nmap-service-probes , or you can specify --allports to scan all ports regardless of any Exclude directive. Enables OS detection, as discussed above. Alternatively, you can use -A to enable OS detection along with other things.
OS detection is far more effective if at least one open and one closed TCP port are found. Set this option and Nmap will not even try OS detection against hosts that do not meet this criteria. This can save substantial time, particularly on -Pn scans against many hosts. It only matters when OS detection is requested with -O or -A. When Nmap is unable to detect a perfect OS match, it sometimes offers up near-matches as possibilities.
The match has to be very close for Nmap to do this by default.
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