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 "https://azportscan.azurewebsites.net/api/PortScanner"
$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 "https://azportscan.azurewebsites.net/api/PortScanner?ports=1234,8080,3389,3333"
$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.

2 Comments

  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 canyouseeme.org 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. 🙂

Leave a comment

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.