![]() With at least one open and one closed port on the target host, Nmap can detect the target OS effectively. MAC address of the host’s Ethernet card, and its manufacturer Not shown: 997 closed ports PORT STATE SERVICE Host 192.168.2.101 is up (0.0030s latency).ĭiscovered the host status in practically no time OS detection uses a combination of ICMP echo, TCP and UDP packets. Initiating OS detection (try #1) against 192.168.2.101 v increases the verbosity of the output. Table 1: Analysing the output of an OS detection scan Table 1 shows a sample output that’s running an OS detection command against a target PC with an Intel Ethernet card, while running Windows XP SP3. Let us study the OS detection command in detail. With so many different operating systems and versions around, it is really interesting how Nmap detects the operating system of a target in a very short time. A FIN scan is initiated using a command like nmap -sF 192.168.100.100. However, by doing so, it reveals its presence. Since there is no earlier communication between the scanning host and the target host, the target responds with an RST packet to reset the connection. Instead of a SYN packet, Nmap initiates a FIN scan by using a FIN packet. ![]() The standard use of a FIN packet is to terminate the TCP connection - typically after the data transfer is complete. The Nmap FIN scan comes in handy in such circumstances. So how does a penetration tester work around this? FIN scan ![]() ![]() Some of the hosts with Intrusion Detection Systems (IDS) and firewalls do watch for SYN packets targeted at particular ports. Let us continue with some more intricacies of Nmap, by discussing various other command-line options.Ī TCP SYN scan (which we have covered earlier) leaves a lot of fingerprints on the target host, thus revealing the identity of the scanning host. ![]() The earlier articles in this series have detailed many important Nmap scan types. Nmap is a fantastic tool, and I just can’t refrain from praising it, every time I use it. ![]()
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