Monitoring with PowerShell: External port scanning part 2

So recurring readers will be reading this title and go “Wait a minute, he already blogged about this” and you’d be right. With the recent Github Sponsorship taking off, I’ve decided to release some more public tools so life can be made easier for other MSPs. In the previous blog I’ve told you to create and upload a port scan file yourself to a web host, some people found it challenging because a lot of hosts block unknown outbound ports.

This is why I’m introducing the Public CyberDrain Remote Port Scan API. I’ll be the first to admit the name could use some work ;). This tool allows you to initiate a remote port scan from anywhere. The tool will only scan the external IP from where the script is launched to prevent abuse.

If you’re worried about privacy, want more granular control, or just prefer to roll your own you can see the code for the port scan tool here and host it yourself instead. 🙂

To start a remote port scan, you can execute the following code.

$Results = invoke-restmethod -uri ""
$OpenPorts = $Results | Where-Object { $_.status -eq "open"}
$ClosedPorts = $Results | Where-Object { $_.status -eq "closed"}
if(!$OpenPorts) {
$PortScanResult = "Healthy"
} else {
$PortScanResult = $OpenPorts

By default the port scan only scans a specific subset of ports namely 21,25,8080,33890,1234,1111,2222,3333,3389,3389,4444,5555,6666,7777,8888,9999,1234, you can add ports to this list by appending the request with your ports as such:

$Results = invoke-restmethod -uri ",8080,3389,3333"
$OpenPorts = $Results | Where-Object { $_.status -eq "open"}
$ClosedPorts = $Results | Where-Object { $_.status -eq "closed"}
if(!$OpenPorts) {
$PortScanResult = "Healthy"
} else {
$PortScanResult = $OpenPorts

As I explained in the older blog; having a remote port scan tool that runs with your RMM is super useful to detect the current state of what you’ve exposed at your edge. It can also help you capture tiny mistakes your engineers have made, or detect places where you might need to reconsider how you access resources.

And that’s it! as always, Happy PowerShelling.

PS: I’ve started a new short youtube series about technologies you could use in your MSP. Check out the blog about that here.


  1. Owen April 6, 2021 at 12:12 am

    Hi Kelvin, This is cool but I am not sure it is functioning correctly. I am scanning ports that I know I have open and your endpoint is returning healthy. I have checked the same port on and it is reporting open.

    1. Kelvin Tegelaar April 6, 2021 at 9:32 am

      Make sure you aren’t geoblocking the outgoing function IP. you can check the IP it has at that moment by pinging the function. 🙂

  2. Paul May 12, 2021 at 9:11 am

    Hi Kelvin, I had the same problem as reported above.

    I did a bit of digging and it appears that the Ports= is being ignored. Se below, I specified the ports using your method above and got the following.

    PS C:\Windows\system32> $Results = invoke-restmethod -uri “,8080,3389,3333,8443”

    PS C:\Windows\system32> $Results

    Port Status
    —- ——
    21 closed
    25 closed
    8080 closed
    3389 closed
    1234 closed
    1111 closed
    2222 closed
    3333 closed
    3389 closed
    4444 closed
    5555 closed
    6666 closed
    7777 closed
    8888 closed
    9999 closed
    1234 closed

  3. Peter January 10, 2022 at 3:32 pm

    Hi Kelvin,

    I tried using the DATTO RMM component method of this script, and it did seem to be working 6 months ago. However, it seems to have stopped working, am I right in saying is no longer operational?


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