Digital Forensics Stream

Findings, tips, and tools developed while trekking through the world of digital forensics
Posted by Jason Hale 
· October 7, 2017 
· 3 Comments

RecentApps Registry Key

While digging into a Windows 10 NTUSER.DAT hive recently, I came across a registry key/subkey hierarchy that was really intriguing.  The top level key, called RecentApps, contained references to several applications and files that had been accessed on the system.  In addition to the application and file name, I found that the path to the application, a launch count, the full path to the file, and the last time the file was accessed was available from the RecentApps key hierarchy.

The RecentApps key is located in the user’s NTUSER.DAT hive at Software\Microsoft\Windows\Current Version\Search\RecentApps. Its general hierarchy looks something like the image below.  Beneath the RecentApps key is a series of subkeys named by GUIDs.  Each GUID subkey directly under RecentApps corresponds to an application.  Some of the GUID subkeys have additional subkeys as well, which correspond to particular files accessed by the application.

RecentApps key hierarchy

Application GUID Subkeys

As mentioned, the subkeys directly under RecentApps are associated with applications.  Each of these GUID subkeys contain values that may be of useful during an examination, such as the full path to the application, a last accessed time, and a launch count.  The LastAccessedTime value is in the ever-popular 64-bit FILETIME format.  In my experience, both the LastAccessedTime and LaunchCount values have been consistent with the last execution and run count data available in the UserAssist key.

RecentApps File Subkey

File GUID Subkeys

Each subkey under an application GUID’s “RecentItems” subkey is associated with a file accessed by the application and is also named by a GUID.  The information included in each file GUID subkey includes the file name, a last accessed time (in some cases), the full path of the file, and more.

The last accessed time, when present, is a FILETIME value and appears to be consistent with the last accessed time available from jump lists in the file system.  Unfortunately, this value does not appear to be populated in many cases.  Windows 10 Professional version 1703 build 15063.483 has been observed with the LastAccessedTime value populated, but in all other tested versions of Windows 10 – both before and after the release of 15063.483 – this value appears to be set to zero.  Fortunately, an access time for the file referenced by the file GUID subkey can be determined using the LastWrite time of the file GUID subkey itself.  Importantly, the LastWrite time does not appear to be updated on subsequent access to the file, so the LastWrite time should not be concluded as the last time the file was accessed without further corroborating evidence from other artifacts.

RecentApps\RecentItems Subkeys

The number of file GUID subkeys under each application GUID key appears to be limited to 10.  Interestingly, the cycling of these subkeys does not appear to be on a first-in-first-out basis (as with many other artifacts in Windows).  Instead, it appears that when an eleventh subkey is added to an application GUID key, the file GUID subkeys are arranged alphabetically by name.  After being arranged alphabetically, the last one in the list is removed.  Since the alphabetization is by GUID, it is inherently random which 10 files that were accessed by an application will be included in the list of file GUID subkeys .  The method of cycling utilized by the file GUID subkeys means that an examiner cannot conclude that the files referenced by these subkeys are the 10 files most recently accessed by a particular application.

Data points such as the RecentApps key hierarchy in Windows 10 help to provide corroborating information to increase an examiner’s overall confidence in his or her findings.  If any type of anti-forensic measures were taken (system or user initiated), locations such as the RecentApps key may also provide information that was deleted from other and more well known areas of the system.

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Categories : Registry Forensics, Windows 10
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Posted by Jason Hale 
· August 14, 2017 
· 6 Comments

Memory Acquisition and Virtual Secure Mode

Starting in Windows 10 and Server 2016, Microsoft added the option to enable various forms of virtualization-based security (VBS).  This feature suite currently includes Credential Guard, Device Guard, Application Guard, and more.  All of these optionts leverage virtual secure mode (VSM), which includes a secure kernel and secure user mode component and is made possible through the use of a hypervisor.  On the forensics side, encountering a system with virtual secure mode or some form of virtualization-based security enabled can have an impact on your investigation.  This post is about one of the more significant impacts I’ve seen thus far: memory acquisition.Physical memory is commonly acquired using a software-based memory acquisition tool such as winpmem, DumpIt, Magnet RAM Capturer, FTK Imager, or one of the several other options available.  These tools typically load a device driver into the kernel and subsequently read memory through mapping the DevicePhysicalMemory object, using a function such as MmMapIoSpace, or directly manipulating the page tables.  Many of these tools also share a similar trait: their use on a system with virtual secure mode enabled results in a system crash.

Result of attempted memory acquisition

Clearly, a BSOD while attempting to acquire physical memory from a system is not ideal.  If the system is an end-user machine, you will likely be left with a frustrated user (not to mention the obvious impact on your memory dump).  If the system is a more critical piece of the organization such as a server, the consequences of a system crash could extend well beyond the impact on your memory dump.  One way to avoid this scenario is to first determine whether virtual secure mode is enabled.One of the easiest ways to determine if VSM is enabled on a live system is to check whether the “Secure System” process is running.  This is the process associated with the secure kernel and, in my experience, serves as the “trigger point” as to whether a system will crash when running several memory acquisition tools.  Simply put, if the “Secure System” process is running, make sure you are using a tool that plays nice with virtual secure mode.

Task Manager view of system with VSM enabled

Most of the memory acquisition tools I’ve tested on a system with VSM enabled result in a system crash shortly after the acquisition driver is loaded.  The tested tools include multiple versions of winpmem, Magnet RAM Capturer, FTK Imager, and older versions of DumpIt.  The table below lists some of the unsuccessful tools I’ve identified.  I should note that the DumpIt v3 issue was not necessarily related to VSM; rather, it was a lack of an EV certificate that prevented the DumpIt driver from loading in the first place.

Fortunately, there are tools that currently dump memory even when VSM is enabled.  The tools I’ve identified at this point are Belkasoft RAM Capturer, Comae Technologies‘ DumpIt v3.0.20170620, and Passmark osforensics v5.1.1001.  There are also some tools that I have not yet been able to test due to licensing issues or otherwise.  These include options such as WindowsSCOPE and the combination of F-Response with a separate acquisition tool.  If anyone has a specific tool or version they would like to see tested, let me know and I’d be happy to give it a shot and report the results as long as the tool is available to me.

Update (9/6/17): I was able to use a trial license of WindowsSCOPE to test memory acquisition from a system with VSM enabled. WindowsSCOPE was not able to acquire a memory dump, but it did not result in a system crash.  Instead, a small error message reported that the selected memory “could not be fetched”.  The table above has been updated with these results.

Update (9/11/17): According to Stick Dave, the lastest version of winen (as of 9/11/17) fails to acquire memory from a system with VSM enabled.  Like many other tools, it fails with a BSOD.

Update (3/23/18): The latest version of DumpIt (3.0.20180307.1) also acquires memory from a system with VSM enabled without causing a BSOD.

Update (9/17/18): The latest version of winpmem now supports acquiring memory from VSN enabled systems.  See here for a detailed description of the fix.

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Categories : Memory Acquisition
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Posted by Jason Hale 
· April 18, 2016 
· 6 Comments

Fun with Recycle Bin $I Files & Windows 10

A few weeks back, I found myself in need of a free tool to parse $I files from Windows Vista+ recycle bins.  For anyone needing a refresher, $I files store metadata regarding the act of sending a file to the recycle bin in Windows Vista and later.  These $I files essentially replace the functionality of the INFO2 file used in Windows XP and store information such as the name and original path of a file before it was sent to the recycle bin as well as the time the file was sent to the recycle bin.  The file format itself is trivial to manually parse in a hex editor, but I wanted to be able to demonstrate the value of the $I files to students in a class I was teaching without the need for a hex editor.  I also wanted the students to be able to easily parse these files on their own.  I was aware of a couple of free tools that parse $I files, but couldn’t find one that was exactly what I was looking for – so I decided to write one and provide it to my students. I doubt that I’m the only one to encounter this, so I’ve released this simple $I file parser in case someone else finds that they have a need for it.  The link is at the bottom of this post for those interested.

One of the intriguing things I came across in writing this tool is that $I files from Windows 10 recycle bins vary slightly from those in Vista through 8.1.  The change is not significant, but it is enough to potentially throw off some $I file parsers.  The slight change also provides us with the ability to distinguish between $I files originating from a Windows 10 system and those originating from a Vista/7/8/8.1 system.  This piece of information could be important in some instances.  For example, if you encounter an $I file in the unallocated space of a Windows 10 system, you could determine if that file was an artifact from a previous non-Windows 10 installation.  Given the ability to distinguish Windows 10 $I files from previous versions, I’ve included a version field in the output of my $I file parser so that this information is reported.The difference I’ve noted between the Windows 10 $I file structure and that from previous versions of Windows is detailed below.

$I structure prior to Win 10

Windows 10 $I structure

 

 

 

 

As you can see, the only structural change in the Windows 10 version appears to be the addition of the file name length field at offset 24.  This will typically result in $I files from Windows 10 systems being smaller than in prior versions since the $I file is only as large as it needs to be.  In prior versions, each $I file was a static 544 bytes.  While not structural, another change can be found in the header/version field.  The header field for Vista, 7, 8, and 8.1 is 0x01, while this field is 0x02 for Windows 10.  This makes it very easy to distinguish between the two versions when parsing.

For those interested, the link to download my $I file parser can be found on the download page here.

6 Comments
Categories : Tool Release/Update, Windows Artifacts
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Posted by Jason Hale 
· July 17, 2015 
· 1 Comment

Adobe Reader’s Not-So-cRecentFiles

Version 11.0.07 of Adobe Reader, released in May 2014, introduced some interesting changes that can impact forensic examination.  With previous versions of Reader for Windows, the cRecentFiles subkey found in the Acrobat Reader subkeys of an NTUSER.DAT hive provided an examiner with the five most recent files accessed by Adobe Reader.  Information about these files was divided into five subkeys named “c1”, “c2”, “c3”, etc., with each subkey containing a bit of information about the accessed file.  Version 11.0.07 of Adobe Reader expanded this capability, tracking much more than just the five most recently accessed files.  Additional information is also recorded about each accessed file, as well as a list of the
five most recently accessed folders.

The screenshot below shows the new look of the “c#” subkeys that store information about recent files accessed in Adobe Reader version 11.0.07 and above.  Note that the full path to these subkeys is found in a user’s NTUSER.DAT hive under “SoftwareAdobeAcrobat Reader<version>AVGeneralcRecentFilesc#”.

Values in a cRecentFilesc# subkey

The new values added to the “cRecentFilesc#”subkeys are
“sDate”, “uFileSize”, and“uPageCount”.  The “uFileSize” and “uPageCount” are pretty self-explanatory, storing the size of the file in bytes and the number of pages in the accessed file, respectively.

sDate value data

The “sDate” value stores the last time that the file was accessed in Adobe Reader.  The “sDate” value type is REG_BINARY, but the value data holds a simple ASCII string of the timestamp.  Interestingly, the time zone offset of the system at the time the file is opened is included in the “sDate” value data.  If the time zone of the system is changed, the offset included in the “sDate” value is reflected accordingly for files that are later opened in Adobe Reader.  This provides examiners with a more more granular view of when files were accessed in Adobe Reader, as previous versions only allowed us to determine the last time the most recent PDF was accessed.

The five most recently accessed folders are also tracked by
Adobe Reader version 11.0.07 and later in a “cRecentFolders” subkey under “HKCUSoftwareAdobeAcrobat Reader<version>AVGeneral”.  Recently accessed folders are maintained in a similar fashion as the recently accessed files, but the level of detail associated with each accessed folder is pretty minimal.  Each “c#” subkey provides us with the name and path of the accessed folder via the tDIText (or sDI) value, and we can correlate the Last Write time of the cRecentFolders subkey with time that the most recent folder was accessed.

Values in a cRecentFoldersc# subkey

Perhaps the most significant change from a forensic perspective in Adobe Reader version 11.0.7 and later is the alteration to the number of files tracked in the cRecentFiles subkey.  Instead of the most five most recent files that are tracked in previous versions, Adobe Reader 11.0.7 appears to track the 50 most recently accessed files.  In version 11.0.9, the maximum number of recently accessed files jumps to 100.  After testing the current version of Adobe Reader DC, 100 still appears to be the maximum.  This means that you could have up to 100 “c#” subkeys under the cRecentFiles key!  After 100 documents have been accessed, the subkeys will be reused in a FIFO fashion as seen in previous versions of Adobe Reader (e.g. the contents of subkey c100 will be removed and replaced with the contents of c99).

cRecentFiles with 100 subkeys

Examiners should be aware of this additional functionality in Adobe Reader in order to take advantage of the historical information it provides.  The cRecentFiles subkey from a user’s active NTUSER.DAT hive can provide a nice list of files accessed by Adobe Reader.  With later versions storing up to 100 “recently” accessed files, the cRecentFiles subkeys could end up storing files that were not-so-recently accessed as well.  Further, when combined with previous versions of the user’s NTUSER.DAT hive from volume shadow copies, an examiner may be provided with quite a detailed history of files accessed using Adobe Reader.

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Categories : Registry Forensics
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Posted by Jason Hale 
· February 4, 2015 
· No Comments

Leveraging the DeviceContainers Key

If you’ve ever examined registry artifacts related to a particular USB device, you’ve probably come across a value called “ContainerID”.  For example, a flash drive’s instance ID subkey of the USBSTOR key includes a ContainerID value.  Prior to Windows 8, a device’s Container ID was probably of little interest to an examiner. However, beginning with Windows 8, a device’s Container ID can be used to help profile a specific device and corroborate findings from other locations.  The CurrentControlSetControlDeviceContainers key of the SYSTEM hive on a Windows 8 machine holds a wealth of information, broken down by Container ID, about devices connected to the system.

Before dissecting the DeviceContainers subkey, it’s important to understand what a container ID represents in the first place.  Starting with Windows 7, container IDs were used to identify a physical device on the system.  This Windows Dev Center page describes a container ID as “a system-supplied device identification string that uniquely groups the functional devices associated with a single-function or multifunction device installed in the computer.”  This “system supplied identification string” is a GUID and is referenced in various locations, including the EnumUSBSTOR and EnumUSB subkeys of the SYSTEM hive, as the “ContainerID”.  One thing to keep in mind is that all physical devices should be assigned a ContainerID – not just storage devices.  This means that when digging into the DeviceContainers key, many of the devices listed may be something other than storage devices (e.g. monitors, external speakers, keyboards, etc.).

DeviceContainersContainerID subkey structure

The screenshot on the right is an example of what you might see when browsing a device’s DeviceContainers subkey.  The top node as well as the subkey to the BaseContainers key is named by the ContainerID value (the same one found in the USBSTOR key).  The Properties subkey contains eight different sets of…. well, properties.  The idea of useful information being found in a set of “Properties” subkeys is not new; Harlan blogged about the Properties subkeys within the USBSTOR key here and Yogesh Khatri wrote about it here as well.  This is a different set of properties, however, than what is found in the USBSTOR key.

While there are numerous bits of data available in the Properties subkey, I will only highlight a few of the items that may prove useful in a typical forensic examination. The table below summarizes some of the information about a device that is available from the DeviceContainers key.  As you can see, the device instance ID, “DeviceContainer_ModelName”, and “DeviceContainer_PrimaryCategory” properties are available here in addition to two 64-bit FILETIME properties.  The “DeviceContainer_ModelName”, and “DeviceContainer_PrimaryCategory” properties are defined in the devpkey.h file of the Windows 8.1 SDK.  In addition to the property subkey listed in the table below, the device instance ID is also available in the subkey named by the device’s Container ID within the BaseContainers key.

 

 

 

The device instance ID is a valuable piece of information, as it contains the VID and PID of a device as well as the serial number or unique identifier of the device.  For example, when connecting a flash drive to a Windows 8.1 system, I found “USBVID_090C&PID_10001009070810017910” to be the device instance ID associated with the flash drive.  In this case, you can see that “1009070810017910” is the serial number of the flash drive; this information can be corroborated with the USB and USBSTOR keys as well.

The DeviceContainer_ModelName helps describe the device – similar to the FriendlyName value of the USBSTOR key.  Examples of what I have seen in this property are “My Passport 0730”, “iPhone”, and “USB DISK”.  The DeviceContainer_PrimaryCategory helps describe the purpose of the device.  Some examples of what I have noted in this property are “Storage”, “Audio”, and “Display Monitor”.

There are also two 64-bit FILETIME timestamps that appear to be consistent with the first time the device was connected to the system.  Specifically, the “3464f7a4-2444-40b1-980a-e0903cb6d912\0007” property appears to contain the time the device driver installation started, while the “3464f7a4-2444-40b1-980a-e0903cb6d912\0008” property appears to contain the time the device driver installation completed.  This theory is supported by the setupapi.dev.log file, which includes the start and end time of device driver installations.  Interestingly, these two timestamps are slightly different than the Install and First Install timestamps found in other Properties subkeys in the registry. Unfortunately I have not yet found a precise definition – such as that from a Windows SDK – for what these two timestamps officially represent.

One of the nice things about the DeviceContainers key is that it appears to group all physical devices that have been connected to a system into one place.  If an examiner is focusing solely on the USBSTOR key, he or she may miss the fact that an MTP device was connected or that a hard drive was connected using something other than USB.  While the DeviceContainers key may not necessarily provide information that cannot be found elsewhere, it serves as yet another source to help examiners corroborate findings from other locations on the system and may be critical in cases where the ordinary sources of device-related information are not available.

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Categories : Registry Forensics
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DISCLAIMER

The contents of this blog reflect my opinion and may not represent the views of my employer or anyone else.  Any material on this blog, especially related to technology and/or forensic methodology should not be assumed to be true in all possible scenarios.  As always, test any theories, ideas, or tools from this blog in your own environment before stating them or the results therefrom as factual.