Audit all windows firewalls on your domain and display the results in a UI using PowerShell Universal

Mar 5, 2022 | Powershell, Scripting and programming, Security, Server administration, Technology | 0 comments

Do you want the code for this? No problem. Just skip down to the heading that says “Code here”.
Yeah yeah yeah. I know that I have given out plenty about Ironman Software and their PowerShell Universal product very strongly on a few different sites. But unfortunately for me, There’s just nothing else on the market that can wrap a nice easy(ish) UI around PowerShell scripts. So stick with me while I explain what I’m doing here.
My need:
Hey, first, lookup something called the star principal. It’s an Amazon Interview technique and I’m going to use it here to explain the last few days quickly and easily.
Star stands for:

  • Situation
  • Target
  • Action
  • Result

So the Situation is:

I need to provide a comprehensive, up to date, reproduceable and accurate report of the status of Windows firewalls on servers.

The Target is:

Re-use a script that I wrote two years ago, warap it in a UI and give that to the director so he can run this report or ask someone else to do it without coming to me any more than one time.


Ah. here’s where it get’s fun.
Firstly, here is how it hangs together:

  1. . I have all the processing in a PowerShell module. I’m comfortable working in the command line so having it in a module full of functions that I have written to get me through the day by removing repeditive tasks suits me well. But it doesn’t suit anyone else. Having PowerShell vomit out text to the director wouldn’t put me on his Christmas list. In fact, I’m already not on his Christmas list. Maybe I should go back to plain text? Pondering for a different day. Sorry. I went off on one there. Anyway, what I’m saying is I want to wrap that in a UI but I don’t want to rewrite code. Re-use and Re-cycle.
  2. I went in to look around PowerShell Universal for the first time in ages. I was getting weird errors when using powerShell5 where it wasn’t recognising stored secrets. But it turns out that the maximum time you can store a secret for is one year. So I suppose that’s just something I missed in some bit of documentation somewhere.
  3. Then, sometime over the past year, I tightened security on all of the service accounts so by by to storing Kerberos tickets in an active user session. This made me rethink how I was handling permissions for this script.
  4. Sometime in the past two years since I wrote this really great function, I got too clever for my own good. In other words, I over complicated it. Initially, I was just passing in a string as a parameter but then sometime, I must have decided that I wanted to throw custom objects with servers in it and I also started using the pipeline. What am I talking about? Okay. I’ll explain briefly.
    This is how you would pass something to a script using a parameter:
    First, let’s say we have an array called $MyWonderfulArray[] with several fields in it. ServerName and TrafficDirection. If the function doesn’t support taking the fields out of the pipeline, we need to explicitly loop through every item in this array and pass it the values for ServerName and TrafficDirection. That sounds kind of slow doesn’t it? Yeah. It is! Here’s an example:
    $ServerVariable = $MyCoolArray[0].ServerName
    $InboundOrOutbound = $MyWonderfulArray[0].TrafficDirection
    MyCoolFunction -Server $ServerVariable -TrafficDirection $InboundOrOutbound
    Now. firstly. You might ask what the idea of the [0] is. That’s just getting the first item in that array. I could loop over the array but this wasn’t meant to be a PowerShell tutorial.
    But now let’s take a quick look at using the pipeline. Let’s say your function expects two parameters. ServerName and TrafficDirection. Well, because these are already specified as fields in my array, I don’t need to explicitly pass them as parameters to the function assuming of course that I have configured the parameter section at the top of the function to support grabbing these fields through the pipeline. So now without needing to loop or even explicitly pass over the fields, I do this:
    $MyWonderfulArray | MyCoolFunction
    See? The pipeline is cool.
    But because I had changed the function, I was encountering infinit loops and some ocasional errors. That wasn’t too difficult to fix. I got it sorted within a few minutes.
  5. I found that tens of thousands of lines were added for some particular servers. Turns out that when ever a user logs into an RDS session host server running 2019, it creates a hole lot of firewall rules for that session. Okay. Anyway, I fixed that. It required painfully removing tens of thousands of rules then applying a registry fix to each session host server so that the problem doesn’t repeat in the future. Still, this took a good three hours tonight because as I was deleting so many rules each time, the MMC snapin kept freezing? Why didn’t I use PowerShell? Well, because there are about 40 other rules in there specific to the applications running on those session host servers and the last thing I want is someone from that facalty calling me on Monday morning with a room full of students anxiously waiting to start their labs while I try to figure out what rule in the tens of thousands that I removed caused this particularly horrible delay to their teaching and learning. so that really wasn’t fun.
  6. Next, I ran the script again but found that for some reason, one of the filters for traffic direction wasn’t working. I’m running this code using invoke-remote and it’s a non-native PowerShell command so sometimes they can behave in unexpected ways. Again, that wasn’t really difficult to sort. A where-object to only return the output that I wanted got around the problem. But you must understand oh most patient reader that each time I ran this script, it could take up to an hour or even two. It’s going across quite a lot of servers and really diving deep into the firewall rules, what they allow and what they reject. So each thing I changed even if it was minor took a long time for it to process.
  7. I had messed around with creating a UI for this a few years ago but I tidied it up tonight. I had a stupid bug in it. It was using the entire count of servers when reporting on the number of bad / dangerous rules. Now I have a separate variable with the count. Why I didn’t just do that a few years ago, I don’t know.


It all works. It took a lot longer than I would have liked but I’m really happy with the result. Something that anyone with the right level of permissions can independently use without my input.

Absolutely nothing in my life has gone to plan this week. Well, all I have had time for is technology problems so I suppose my life has just been technology. still though. I still need to get to another job tomorrow where I installed Cuda but the GPU isn’t found after a reboot. I spent three hours on that on Wednesday evening but now the person just wants me to install Docker and use Cuda and Kaldi through containers instead. That’s going to be another truck lode of fun but it’s going to have to wait until tomorrow because I’m tired.
Hey, for the record, I’m not really a fan of Nvidia at the moment either. Their documentation is out of date, their drivers are out of date and they mis and match terms. For example, at the top of the driver support page, they talk about Tesla T4 but then down the page they say how the driver only supports series 9 and above. How the hell am I meant to know what series the Tesla T4 is? Anyway, sorry. I’m rambling again.
Because I’m feeling very generous, here’s some code that will just change your life if you are administering a lot of Windows servers and you need to audit all the firewall configs.

The Code!


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