Verifying what computer you connect to, using PowerShell

Purpose

You want to verify that the computer you are connecting to is the actual target you expect. Some of the issues this will rule out will be a misconfigured DNS resulting in stale, shared, or duplicated IPs.

Resolution

This requires your environment allows the commands Get-WmiObject or Get-CimInstance to run in a remote PowerShell.

Run this script, but first let's go over what this thing is doing.

1. Initially the script will need the target we want, we'll let it prompt for a new one each time the script is run. We'll call a few variables and make them null values so this will be able to run reliably in the same console multiple times for different targets.

2. Then we will need to get the DNS records for the hostname of the target. We will use Resolve-DnsName and then pull out the IPs returned and insert them into an array since some targets can have multiple IPs we will want to test each of them. For each IP found we will test to make sure they respond, if they do not then we will remove them from the array.

3. Then we will feed what the target reports itself as into the variable $actualTarget by way of a Get-CimInstance call. If that call fails we will silently move to it trying a Get-WmiObject call. (If this step fails your environment may have restrictions for PowerShell, WinRM, or remote WMI connections).

4. Then we will throw this into a Test-NetConnection to verify that we can connect on a required port using the hostname claimed by the target (for each IP returned). The IP address returned here may not match what DNS returns when the target has multiple IPs and that is ok this will be what the target reports it's IP as. It is the $actualTarget and if the TCPTestSucceeded is true or not that we want to pay attention to.

# Requires -Version 3
param (
[Parameter(Mandatory = "True")]
[String]$ComputerName
)

# This is to reset any variables from previous runs
$IP = @($null)
$actualTarget = $null
$address = $null

# Grab all IPv4 addresses registered to the ComputerName, if you would like to search IPv6 also remove the parameter "-Type A"
Try {
$IP = (Resolve-DnsName $computerName -Type A -ErrorAction "Stop" | Select-Object -Property IPAddress).ipaddress
} Catch {
Throw "The ComputerName entered does not have a valid IP"
}

# Test if the IP responds- if not we need not continue- We'll remove the non working IP from the $IP array
ForEach ($address in $IP){
If ((Test-Connection $address -count 1 -quiet) -eq $false){
$IP = $IP | Select-Object -Skip 1
}
}

# If the Test-Connection fails the address was removed above, if all IPs were removed then we will throw a terminating error, no reason to continue
If ($IP.COUNT -eq 0 ){
Throw "The IPs returned from DNS failed the connection test, be sure the target is powered on and responds to a ping."
}

# Bring in the results list Object so we can filll it up later
$Results = New-Object System.Collections.Generic.List[Object]

# For every address we found registered to the target and passsed the Test-Connection step we'll loop in our tests-
ForEach ($address in $IP){

# Initially we will attempt a Get-CimInstance method to grab the hostname- these methods will require permissions for the respective types of attempts.
Try {
$ActualTarget = (Get-CimInstance -ClassName "Win32_ComputerSystem" -ComputerName $ComputerName -ErrorAction "Stop").Name
} Catch {
# If the Get-CimInstance fails we can silently move to attempt a Get-WmiObject- if both fail we will write an error for this IP tested
Try {
$actualTarget = Get-WmiObject -class Win32_ComputerSystem -property Name -ComputerName $address | select -expand Name -ErrorAction "Stop"
} Catch {
Write-Error "The WMI call to $address failed or the target is offline- Ensure you can remotely manage this target with PowerShell and it is powered on. Be user you are logged in as an admin. You may need to check or enable WinRM, PSRemoting, or Execution Policies"
}
}

# This will test the SMB connection on port 445 with the name that was returned by the connected host not necessarily the ComputerName given
$connectionTest = Test-NetConnection -computername $actualTarget -port 445

# This will feed the data gathered into the $Results list we generated earlier
$Results.Add([PSCustomObject]@{
"Expected Target" = $ComputerName
"IP Address we found" = $Address
"Actual Target" = $ActualTarget
"Test Successful" = $ConnectionTest.TcpTestSucceeded
})
}

# This will display the $Results list we filled up with the things.
$Results