Idle Zombie Scan Nmap: Nmap is a TCP port Scan method used to send a spoofed source address to a computer to find out what services are available and offers blind scanning of a remote host.

This is accomplished by impersonating another computer.No packet is send from own IP address, instead another host used called as Zombie.

Finding a Zombie first

The first step in executing an IP ID idle scan is to find an appropriate zombie. It needs to assign IP ID packets incrementally on a global (rather than per-host it communicates with) basis.

When an idle scan is attempted, Nmap tests the proposed zombie and reports any problems with it. If one doesn’t work, try another


Choosing a network near your source address, or near the target, produces better results. You can try an idle scan using each available host from the ping scan results until you find one that works.

Steps Involved in Idle Scan

First we need to send a session establishment ‘SYN‘ packet to determine whether the port is open or close.

If the port open the ‘Zombie‘ responds with a ‘SYN/ACK‘ containing IPID of remote host.If the port closed then it will send ‘RST‘ packet.

Idle Zombie Scan Nmap
Idle Zombie Scan Nmap

Idle Zombie Scan Nmap

Once a suitable zombie has been found, performing a scan is easy. Simply specify the zombie hostname to the -sI option and Nmap does the rest.

Here consider

Zombie :

Target :

  • -Pn Scan only selected ports and ignore discovery
  • -p Scan a single port
  • -sI TCP Idle scan

Scanning : [email protected]:~# nmap –Pn –p –sI

Parallelizing idle scan is trickier than with other scan techniques due to indirect method of deducing port states.

If Nmap sends probes to many ports on the target and then checks the new IP ID value of the zombie, the number of IP ID increments will expose how many target ports are open, but not which ones.

Reliability is another major idle scanning concern. If the zombie host sends packets to any unrelated machines during the scan, its IP ID increments. This causes Nmap to think it has found an open port.

Advantages of Idle Zombie Scan Nmap

Idlescan’s method of spoofing IP addresses allows nmap to find open ports from a distance, even if packet filters are in place.

Nmap simply requires any open port to a zombie workstation to complete the communication process.

One of the largest advantages of idlescan is the stealth factor. A destination station will never see the IP address of the nmap station.

Disadvantages of Idle Zombie Scan Nmap

Idlescan only locates ports. Idlescan can’t provide any application version information or operating system fingerprinting.

The zombie must be an idle station, and that’s difficult to know for sure. Often, many different devices will be tested with idlescan before an appropriate idle station is identified

Idlescan requires privileged access to create the spoofed IP frames. Without privileged access, this scan will not run.

Common Defense against Idle scan

Don’t use a public host in front of your firewall that uses a predictable IPID sequence.

Solaris and Linux are two operating systems that are not vulnerable to this type of behavior.

We should Use a firewall that can maintain state-on connections, determine whether someone initiated a phony session request, and drop those packets without a target host response.

Use an ingress filter on your network to ensure that no packets enter your outside boundary with a source address of your internal network.

With egress filter on your network to ensure that no packets leave your network with a source address that isn’t a part of your internal network.


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