Baker Street Forensics

January 2020, the last time I had work related travel, seems like an eon ago. Later that year I had planned my first attendance at the Magnet User Summit in Nashville. Then COVID entered the scene and every event going forward for me was remote only. Don’t get me wrong, I’m an introvert and being able to work from home in my fortress of solitude the past few years has been great. I even managed to present at Magnet Enterprise Pulse and the HTCIA International Summit, both remotely. Fast forward to the present and events are starting to open back up.

The Magnet User Summit in April will be supporting in-person and virtual attendance. After two years as virtual participant I’ll finally be able to attend in person. As it turns out I’ll be presenting at the conference as well! It’s taken me a few years to get here, but now I get to attend as a speaker (and and employee!)

You can register for the Magnet User Summit (in person or virtual) here:

https://www.magnetforensics.com/magnet-user-summit-2022/

I hope to see you there, be it virtual or in person. And feel free to track me down for Baker Street Forensics stickers if you’re there.

Earlier today I was asked for a ‘quick and easy’ PowerShell to grab a packet capture on a Windows box. I didn’t have anything on hand so I set off to the Google and returned with the necessary ingredients.

The star of the show is netsh trace, which is built into Windows. If we wanted to capture for 90 seconds, start the trace, wait 90 seconds, and stop it the syntax would be:

netsh trace start capture=yes IPv4.Address=192.168.1.167 tracefile=c:\temp\capture.etl
Start-Sleep 90
netsh trace stop

Note there are 3 lines (the first may wrap depending on windows size)

Like Wireshark, you need to specify what interface you want to capture traffic from. In the example above 192.168.1.167 is the active interface I want to capture. But what if I want to use this for automation and won’t know in advance what the active IP address will be?

We can grab the local IPv4 address and save it as a variable.

#Get the local IPv4 address
$env:HostIP = (
    Get-NetIPConfiguration |
    Where-Object {
        $_.IPv4DefaultGateway -ne $null -and
        $_.NetAdapter.Status -ne "Disconnected"
    }
).IPv4Address.IPAddress

Now putting the two together:

$env:HostIP = (
    Get-NetIPConfiguration |
    Where-Object {
        $_.IPv4DefaultGateway -ne $null -and
        $_.NetAdapter.Status -ne "Disconnected"
    }
).IPv4Address.IPAddress
netsh trace start capture=yes IPv4.Address=$env:HostIP tracefile=c:\temp\capture.etl
Start-Sleep 90
netsh trace stop

Perfect. Automated packet capture without having to install Wireshark on the host. The only item you should need to adjust will be the capture (sleep) timer.

But wait, the request was for a pcap file. Not a .etl. Lucky for us there’s an easy conversion utility etl2pcapng. Execution is as simple as giving the exe the source and destination files.

./etl2pcapng.exe c:\temp\capture.etl c:\temp\capture.pcap

That’s it. We’re now able to collect a packet capture on Windows hosts without adding any additional tools. We can then take those collections and convert them with ease to everyone’s favorite packet analyzer.

I’ve combined everything above into QuickPcap.ps1 available on my GitHub site.

In this case the capture and conversion are running as one contiguous process, but it’s easy to imagine them as separate automation elements being handled through scripting by different processes. After all, we all build our Lego’s differently, don’t we?

Baker Street Forensics

Summit Bound

QuickPcap – Capturing a PCAP with PowerShell