Forensic Friday: Get-ForensicChildItem

[This is a continuation of my Forensic Friday series.  Every Friday I provide a short post on a forensic topic of interest or PowerForensics functionality (such as cmdlet descriptions, use cases, and details about lesser known features). Subscribe to Invoke-IR so you don’t miss a Forensic Friday!]

Welcome to another edition of Forensic Friday. I've been incredibly busy this week, but I want to touch on a very useful cmdlet called Get-ForensicChildItem. Those with a PowerShell background can probably guess what Get-ForensicChildItem does. For those that are new to PowerShell Get-ChildItem is the cmdlet that is used for directory listings (among other things). Get-ForensicChildItem performs the same task, but without the Windows API. It parses the Master File Table (MFT) to find the entry for the target directory and outputs a list of files the directory contains.

To understand what is happening it’s important to know that NTFS treats directories just like any other file. This means that directories each have an entry in the MFT. All NTFS does to differentiate a directory file from a data file is flip a bit in a flag field and adds special $INDEX_ROOT and $INDEX_ALLOCATION attributes to the directory file’s MFT entry. Get-ForensicChildItem parses these attributes to return the contents of a directory (including System and Hidden files).

Common Use

List all children of a directory (example targets the root of the C: volume):

Get-ForensicChildItem -Path C:\

List the children of the current working directory (example uses the C:\temp directory):

Get-ForensicChildItem

Return an MFT entry for every file in a directory (example uses the root directory of the C: volume):

Get-ForensicChildItem -Path C:\ | Get-ForensicFileRecord

Forensic Friday: Get-ForensicMftSlack

[This is a continuation of my Forensic Friday series.  Every Friday I provide a short post on a forensic topic of interest or PowerForensics functionality (such as cmdlet descriptions, use cases, and details about lesser known features). Subscribe to Invoke-IR so you don’t miss a Forensic Friday!]

Happy Friday and welcome to another installment of my Forensic Friday series. This week we are going to cover PowerForensics’ Get-ForensicMftSlack, a cmdlet that returns Master File Table (MFT) slack space. For those not familiar with the concept of slack space, it is simply defined as unused space on the disk. MFT slack is specifically the unused portion of a Master File Table record entry. By default, the Master File Table is composed of records that represent a partitions files and directories. Each MFT record has a set number of bytes reserved for it on the hard drive, typically 1024 bytes (the number of bytes reserved for the MFT record entry can be found in the Volume Boot Record). When a MFT record entry does not use all of the bytes that have been allocated to it, the remaining bytes are referred to as MFT slack space, an area on disk that attackers have been known to hide their tools.

Lets use PowerForensics to provide a specific example of MFT slack space. We start by using Get-ForensicFileRecord to get a specific FileRecord object (MFT record entry). Each FileRecord object has an AllocatedSize and a RealSize parameter. AllocatedSize represents the number of bytes that have been reserved for this particular MFT file entry, while RealSize represents the number of bytes that are actually being used by the entry.

Below you can see a hex dump of the MFT File Record. You can see the FILE0 signature and a couple human readable strings (such as “access.log”).

Now if we compare the output of Get-ForensicMftSlack, we see the same data that is at the bottom of the previous picture. This is the slack space! Sometimes slack space can contain contents of deleted files or file system structures.

The image below shows that the difference between AllocatedSize and RealSize is the same as the number of bytes returned by Get-ForensicMftSlack.

Common Use

Parse all Master File Table slack space for a given volume (Example using volume “C:”):

$bytes = Get-ForensicMftSlack -VolumeName C:

Parse MFT record based on Index/Record Number (Example with Index 0 on Volume N:):

Get-ForensicMftSlack -VolumeName N: -Index 0 | Format-Hex

Forensic Friday: Invoke-ForensicDD

[This is a continuation of my Forensic Friday series.  Every Friday I provide a short post on a forensic topic of interest or PowerForensics functionality (such as cmdlet descriptions, use cases, and lesser known features). Subscribe to Invoke-IR so you don’t miss a Forensic Friday!]

Happy Forensic Friday! This week I am taking us back to the basics with Invoke-ForensicDD. Pretty much every Forensicator/Incident Responder has used the Unix dd utility during their day, but I figured it’d be pretty cool to have a PowerShell implementation. This cmdlet provides read only access to the physical disk or logical volume, and returns the requested data as a byte array.

For a practical example of Invoke-ForensicDD, check out my Copying Locked Files with PowerForensics post. Not only does this show leveraging Invoke-ForensicDD to copy a locked file, the post also shows how PowerForensics builds on this functionality to provide more user friendly APIs.

Common Use
Like the unix dd utility, Invoke-ForensicDD has an -InFile parameter that should be used to point at the physical drive (\\.\PHYSICALDRIVE0) or logical volume (\\.\C:). An optional -OutFile parameter directs the output to a file instead of PowerShell’s output stream. The -Offset, -BlockSize, and -Count parameters provide instructions regarding what data to return (-Offset and -BlockSize must be divisible by the physical disk’s sector size, typically 512 bytes). Like Unix’s dd, -BlockSize represents the number of bytes to read at one time while -Count represents the number of BlockSize chunks to read. By default, -Offset has a value of 0 (the beginning of the file) and -BlockSize has a value of 512 (the smallest number of bytes that can be read at once).

This example reads 512 bytes from the beginning of the physical disk (\\.\PHYSICALDRIVE0) and passes the output to Format-Hex:

Invoke-ForensicDD -InFile \\.\PHYSICALDRIVE0 -Count 1 | Format-Hex

Read the first 512 bytes from the logical volume (\\.\C:) and write output to C:\evidence\VBR:

Invoke-ForensicDD -InFile \\.\C: -OutFile C:\evidence\VBR -Offset 0 -BlockSize 512 -Count 1