Forensics – Page 7 – Baker Street Forensics

Ginsu: A tool for repackaging large collections to traverse Windows Defender Live Response

Enterprise customers running Windows Defender for Endpoint have a lot of capability at their fingertips. This includes the Live Response console, a limited command shell to interact with any managed Defender assets that are online. Besides its native commands you can also use the console to push scripts and executables to endpoints.

Note: there is a specific security setting in the Defender console if you want to allow unsigned scripts.

Microsoft has its own triage package capability, but you can also push your own tools like Magnet RESPONSE or KAPE. With a little bit of PowerShell mojo you can use your favorite collection utilities using the Defender Live Response console as your entry point into the remote asset.

The console enables you to pull back files from the remote endpoint, even when it’s been quarantined. One limitation of this console function is that you’re limited to retrieving files of 3GB or less.

For many triage collections this could be under the limit, but depending on the artifacts you’re collecting you might exceed that. So what do you do when you have an isolated endpoint but you need to pull back files over 3GB? That’s where Ginsu comes in.

Ginsu is a PowerShell script that you can upload to your Defender console along with the command line version of 7zip. You configure the script with the directory with the contents you want to transfer. The script acts as a wrapper for 7zip and will create a multipart archive, splitting the files into 3GB segments.

Once you pull the archives back to your workstation, you can use 7zip to extract the files back into their original properties.

In testing, the file transfer capabilities were a bit buggy, whether it was transferring 3GB Ginsu files or other smaller files from the asset. I’m hoping this improves as the Defender console matures. If you’re able to text Ginsu in your environment, I’d love to hear how it performs.

You can download Ginsu from my GitHub repo at https://github.com/dwmetz/Ginsu

Huntress CTF: Week 4 – Forensics: Bad Memory

CTF, DFIR, Forensics, Memory Analysis

Bad Memory

I spent a bit of time on this trying to get Volatility 2 to work with the Mimikatz plug-in. I was not successful. I was able to run the Volatility hashdump module.

I switched to Volatility3 and ran hashdump. For whatever reason the output of Volatility3 was different.

The only user besides the default accounts is for ‘Congo.’ Copy the hashed password and head over to https://hashes.com/en/decrypt/hash where we can search for the hash.

Yay, we got a match.

[Note: anecdotally I was advised that you could do this offline as well with Hashcat and the rockyou wordlist. I had tried that earlier but was using the Volatility2 output. 😦 ]

The last step is to convert ‘goldfish#’ to MD5.

Now just wrap it in the flag { } and you’re good to go.

Use the tag #HuntressCTF on BakerStreetForensics.com to see all related posts and solutions for the 2023 Huntress CTF.

Huntress CTF: Week 3 – Forensics: Rogue Inbox, Texas Chainsaw Massacre: Tokyo Drift

CTF, DFIR, Forensics

Rogue Inbox

Originally I was looking at this in Timeline Explorer, but decided to switch to Excel.

Swimming and scanning through a sea of log entries, an anomaly showed itself.

For this one I just copied the values out by hand.

Huntress CTF: Week 3 – Forensics: Rogue Inbox, Texas Chainsaw Massacre: Tokyo Drift

The download is Application Logs.evtx

If you open the log with Event Viewer, you may see there’s an entry for a (non-actual) event ID of 1337.

The error content isn’t very helpful.

Let’s take a hint from the title and run the event log through Chainsaw.

Nothing significant when using the stock rules. What if we poke specifically at Event ID 1337.

That looks interesting.

Copy the binary data and bring it over to CyberChef

From unintelligible binary to unintelligible PowerShell.

Copy the output and save it is a .ps1 file. We can run the script through PowerDecode.

PowerCode works down through the obfuscation layers, finally revealing the plain text of the command.

Now that the code has been deobfuscated, time to figure out what it does. I copied the code into PowerShell ISE and start isolating the different command sections.

One of the commands does a DNS lookup and directs the output into a string.

If we run the command on its own we can see the output. The last part of the script checks to see if the output matches the pattern of a Base64 encoded string, and if so, decodes it.

Now what was that about Tokyo?

Use the tag #HuntressCTF on BakerStreetForensics.com to see all related posts and solutions for the 2023 Huntress CTF.

Huntress CTF: Week 2 – Forensics: Wimble, Opposable Thumbs, Tragedy_Redux

CTF, DFIR, Forensics

Wimble

Once the file was downloaded and extracted from the zip I ran the file command on it.

OK so we’ll be doing the analysis for this one on a Windows box to start.

Move the file to windows and rename to Fetch.wim

Open the .wim with 7zip explorer

Within the zip file we see a plethora of Prefetch (.pf) files, but among them we there is a fetch.zip

When we extract the contents of the zip file we have another directory of Prefetch files.

I extracted the .pf files to a folder.

I used Magnet AXIOM to process the prefetch files. Based on our scenario, I have keywords set for Huntress, ctf, and flag.

That was easy.

Opposable Thumbs

I know for a fact that Axiom can process thumbnail caches.

And BAM! there’s the flag.

Tragedy Redux

First things first, let’s get an idea of what kind of file we’re dealing with. Hmm. It shows as a zip archive. When the file is unzipped we see the structure below.

Looking at the structure, as seasoned analyst may identify that the tragedy_redux file is in fact a word document. Which will bring up another method in a minute. But before that let’s take a look at the vbaProject.bin file with olevba.

There’s a macro file with some curious fruit and vegetable related functions.

If you realized at the beginning this was a word doc file, you could append the file extension .docm to the file.

When opening the file in Word, there is a prompt to enable macros.

Once the document is open you see a document containing the definition of Tragedy.

From there we can go to Tools > Macros > Edit… we can get to the same vbs content we did with olevba.

The next step was to convert the vbs into something actionable. I struggled on this one, but one of my teammates was successful in converting the vbs to Python.

This code interprets the numeric values in longstring (Apples), as decimal representations of ASCII values, subtracts 17 from each value, and prints the corresponding characters. The characters are printed one by one without newlines, forming a string of characters as the output.

When we run the Python script we get back:

powershell -enc JGZsYWc9ImZsYWd7NjNkY2M4MmMzMDE5Nzc2OGY0ZDQ1OGRhMTJmNjE4YmN9Ig==

Now we can echo the value to base64 decrypt and get our final flag value.

Use the tag #HuntressCTF on BakerStreetForensics.com to see all related posts and solutions for the 2023 Huntress CTF.