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How to identify active hosts in your networks and perform horizontal TCP port scans

Introduction

 

This article provides a PowerShell script which is intended to help security teams and administrators to identify active hosts in their networks as well as to perform horizontal TCP port scans.

 

How is the script working

 

The script provides three options:

1.      Connectivity test (Ping only):

·        The script will identify hosts responding to ping in your networks. No port scanning will be performed. Only active hosts will be displayed.

2.      TCP connectivity test for responding hosts (Ping test first):

·        The script will identify hosts responding to ping in your networks. Once an active host is identified, it will try to connect over TCP to the port you have specified. Only active hosts responding over TCP for the specified port will be displayed. This option is the most recommended one when performing horizontal TCP port scans. However, it is ineffective if your hosts are configured to not respond to ping.

3.      TCP connectivity test for all hosts:

·        The script will try to connect over TCP to the port you have specified for all IP addresses within your subnets. It is a less recommended method as it takes a long time to end its execution. However, it is effective in environments where hosts are configured to not respond to ping.

 

Input

 

The script input is as follows:

·        List of subnets: You will need to specify at least one subnet (Example: 10.31.16.0/22) and it is possible to use multiple subnets with “,” as delimiter (Example: 10.31.16.0/22,192.168.0.0/24)

·        TCP Port: You will need to specify the TCP port to scan (Example: 3389) if you use the options 2 or 3 from above.

 

Script

 

You will need to copy the code above to a .ps1 file and use PowerShell to execute it.

 

The script includes code snippets that have been taken from Microsoft Repository: https://gallery.technet.microsoft.com/scriptcenter/PowerShell-Subnet-db45ec74 Jump

 

## Functions

function Show-Menu

{

 param (

 [string]$Title = 'Scan Menu'

 )

 cls

 Write-Host "================ $Title ================"

 Write-Host "Connectivity test (Ping only): Press '1' for this option."

 Write-Host "TCP connectivity test for responding hosts (Ping test first): Press '2' for this option."

 Write-Host "TCP connectivity test for all hosts: Press '3' for this option."

 Write-Host "Q: Press 'Q' to quit."

}

function connectivity-test

{

 param (

 [string]$IPAddress,

 [int]$scantype,

 [int]$portnumber

 )

 if (($scantype -eq 1) -OR ($scantype -eq 2))

 {

 $testresult = Test-Connection $IPAddress -Quiet

 if ($testresult -eq $true)

 {

 if ($scantype -eq 1)

 {

 $message = "Host " + $IPAddress + " is responding";

 Write-Host $message -ForegroundColor black -BackgroundColor green

 }

 if ($scantype -eq 2)

 {

 $testresulttcp = Test-NetConnection -Computer $IPAddress -Port $portnumber

 if ($testresulttcp.TCPTestSucceeded -eq $true)

 {

 $message = "Host " + $IPAddress + " is listening on TCP/" + $portnumber + "";

 Write-Host $message -ForegroundColor black -BackgroundColor green

 }

 }

 }

 }

 else

 {

 $testresulttcp = Test-NetConnection -Computer $IPAddress -Port $portnumber

 if ($testresulttcp.TCPTestSucceeded -eq $true)

 {

 $message = "Host " + $IPAddress + " is listening on TCP/" + $portnumber + "";

 Write-Host $message -ForegroundColor black -BackgroundColor green

 }

 }

}

   

function Get-IPs {

   

 Param(

 [Parameter(Mandatory = $true)]

 [array] $Subnets

 )

   

foreach ($subnet in $subnets)

 {

   

 #Split IP and subnet

 $IP = ($Subnet -split "\/")[0]

 $SubnetBits = ($Subnet -split "\/")[1]

   

 #Convert IP into binary

 #Split IP into different octects and for each one, figure out the binary with leading zeros and add to the total

 $Octets = $IP -split "\."

 $IPInBinary = @()

 foreach($Octet in $Octets)

 {

 #convert to binary

 $OctetInBinary = [convert]::ToString($Octet,2)

   

 #get length of binary string add leading zeros to make octet

 $OctetInBinary = ("0" * (8 - ($OctetInBinary).Length) + $OctetInBinary)

   

 $IPInBinary = $IPInBinary + $OctetInBinary

 }

 $IPInBinary = $IPInBinary -join ""

   

 #Get network ID by subtracting subnet mask

 $HostBits = 32-$SubnetBits

 $NetworkIDInBinary = $IPInBinary.Substring(0,$SubnetBits)

   

 #Get host ID and get the first host ID by converting all 1s into 0s

 $HostIDInBinary = $IPInBinary.Substring($SubnetBits,$HostBits) 

 $HostIDInBinary = $HostIDInBinary -replace "1","0"

   

 #Work out all the host IDs in that subnet by cycling through $i from 1 up to max $HostIDInBinary (i.e. 1s stringed up to $HostBits)

 #Work out max $HostIDInBinary

 $imax = [convert]::ToInt32(("1" * $HostBits),2) -1

   

 $IPs = @()

   

 #Next ID is first network ID converted to decimal plus $i then converted to binary

 For ($i = 1 ; $i -le $imax ; $i++)

 {

 #Convert to decimal and add $i

 $NextHostIDInDecimal = ([convert]::ToInt32($HostIDInBinary,2) + $i)

 #Convert back to binary

 $NextHostIDInBinary = [convert]::ToString($NextHostIDInDecimal,2)

 #Add leading zeros

 #Number of zeros to add

 $NoOfZerosToAdd = $HostIDInBinary.Length - $NextHostIDInBinary.Length

 $NextHostIDInBinary = ("0" * $NoOfZerosToAdd) + $NextHostIDInBinary

   

 #Work out next IP

 #Add networkID to hostID

 $NextIPInBinary = $NetworkIDInBinary + $NextHostIDInBinary

 #Split into octets and separate by . then join

 $IP = @()

 For ($x = 1 ; $x -le 4 ; $x++)

 {

 #Work out start character position

 $StartCharNumber = ($x-1)*8

 #Get octet in binary

 $IPOctetInBinary = $NextIPInBinary.Substring($StartCharNumber,8)

 #Convert octet into decimal

 $IPOctetInDecimal = [convert]::ToInt32($IPOctetInBinary,2)

 #Add octet to IP

 $IP += $IPOctetInDecimal

 }

   

 #Separate by .

 $IP = $IP -join "."

 $IPs += $IP

   

   

 }

 $IPs

 }

}

   

   

## Main Code

do

{

 $IPSubnets = Read-Host "What are your IP ranges to scan? (Example: 10.31.16.0/22,192.168.0.1/24)"

 Show-Menu

 $input = Read-Host "Please make a selection"

 switch ($input)

 {

 '1' {

 cls

 Get-IPs -Subnets $IPSubnets | % {connectivity-test $_ 1 0}

 } '2' {

 cls

 $port = Read-Host "What is the TCP Port to scan?)"

 cls

 Get-IPs -Subnets $IPSubnets | % {connectivity-test $_ 2 $port}

 } '3' {

 cls

 $port = Read-Host "What is the TCP Port to scan?)"

 cls

 Get-IPs -Subnets $IPSubnets | % {connectivity-test $_ 3 $port}

 } 'q' {

 return

 }

 }

 pause

}

until ($input -eq 'q')