Friday, February 21, 2014

Office 2013: More MRUs

Microsoft Office 2013 continues to yield very interesting artifacts related to user activity. Harlan recently posted about the "PendingChanges" subkeys in relation to PowerPoint, and I have previously posted about MS Word's "Reading Locations" subkeys as well as the last saved location metadata in Excel 2013 spreadsheets.  The registry, specifically the NTUSER.DAT hive, has been particularly interesting in terms of the Office 2013-related information it stores.   

In Harlan's earlier post, he identified references to the PowerPoint presentation he had opened in PowerPoint 2013 in the "File MRU" and "Place MRU" subkeys of "HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Excel\User MRU\LiveId_xxx". The "File MRU" and "Place MRU" subkeys appear to track files and directories recently accessed by the application, with the "Item 1" value corresponding to the most recently accessed item, "Item 2" the next most recently accessed, etc..

Office 2013 Sign in Option
When a user is not signed into a Live ID account, references to the files and directories recently accessed by PowerPoint, Word, and Excel are stored in the "HKEY_CURRENT_ USER\Software \Microsoft\Office\15.0\[programName]\File MRU" and "HKEY_ CURRENT_USER\Software \Microsoft\Office\15.0\ [programName]\Place MRU" subkeys.  When a user signs into a Live ID account (using the Office 2013 sign in option), the recently accessed files and directories appear to be tracked in "HKEY_ CURRENT_USER\Software\Microsoft\Office \15.0\[programName]\User MRU \LiveId_xxx\" under the respective File and Place MRU subkeys.

Interestingly, it appears that a new LiveId_xxx subkey is created each time a new Live ID account is signed in to through the Office 2013 interface.  Based on my limited testing thus far, the File and Place MRUs of each LiveId_xxx subkey appear to be updated independently from one another (updates depend on which Live ID account is signed in) as well as independent from the File and Place MRUs maintained when a user is not signed into a Live ID account.  This means that you could see multiple sets of File and Place MRUs per application, all within a single NTUSER.DAT hive!

HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Excel Subkey

As Harlan mentioned in his previous post, each Item # value in the File and Place MRU subkeys should contain data similar to "[F00000000][T01CF2DF40FEB4220][O00000000]*Z:\Files\Presentation1.pptx", with the value in the second set of brackets being a FILETIME structure that corresponds to the last time the file or directory was accessed from the application.  This means that not only do we have an independent File and Place MRU subkey for each Live ID account that signed in to the system (as well as a File and Place MRU for when the user is not signed into a Live ID account), but we are also provided with the last time each item within each MRU list was accessed.  

Regardless of whether a Live ID account was signed in or which Live ID account was used to access a file, usage history still appears to be recorded in the familiar RecentDocs subkey as well as the application's associated jump list.  These artifacts can serve to provide a file access history (regardless of the Live ID account used to access the file) as well as to help correlate and confirm data located in other artifacts.

Based on initial testing, the File and Place MRU list per Live ID account does not appear to be updated properly on Windows 7 running Office 2013.  More research will be necessary to determine the value and reliability of this artifact under Windows 7. The majority of my testing as it relates to the File and Place MRUs has been with Windows 8.1, which appears to be consistent in updating the appropriate MRU list.  I've only tested the addition of Live ID-associated File and Place MRUs with Word, Excel, and PowerPoint 2013, so the differences in MRUs as compared to previous versions of Office likely extend beyond these three applications.

Thursday, February 13, 2014

VSC Toolset Update

I've made various updates to VSC Toolset since its last public release in September 2012 and wanted to write a quick post about some of the updates for those interested. The most significant additions to the tool have been two new batch scripts: one for comparing the contents of a directory between two VSCs and one for extracting the USB device connection and disconnection events from one or more VSCs (based on the event log and Event IDs detailed here).  There have also been numerous user interface and general usability enhancements made to the tool.  Read on for more details, or you can skip to the VSC Toolset page to download the latest version.

CompareDirectory Batch Script

It can be helpful to see how the contents of a directory have changed over time.  For example, identifying how an employment contract has been updated, not updated, or even created and deleted over a period of time can be critical in accomplishing the goals of your examination.  VSC Toolset previously supported (and still supports) running a batch script utilizing diff.exe to compare two VSCs, but that may be overkill in many cases.  Being able to specify a particular directory for comparison is much quicker and helps to eliminate the noise found in the output of running diff.exe against the entire VSC.

The "CompareDirectory" batch script addition to VSC Toolset works by first creating a file listing of each directory to be compared using the "dir" command.  It then compares the two directory listings using diff.exe, generating output similar to the screenshot below.

CompareDirectory Batch Script Sample Output

EventLogUSB-Win7 Batch Script

In my last post, I introduced a batch script that can be executed against a Microsoft-Windows-DriverFrameworks-UserMode/Operational event log originating from a Windows 7 system to identify USB device connection and disconnection events.  In order to port over a version of the batch script compatible with VSC Toolset, I made a couple of slight modifications (primarily to the input variables).  Simply select the linked VSCs against which you want to execute the batch script and click "Run Command"; VSC Toolset takes care of the rest (with some help from Log Parser).  A separate CSV file containing the USB connection and disconnection events is created for each VSC the batch script is executed against.  Note that you'll need the LogParser.exe and LogParser.dll file in the same directory as the VSC Toolset executable for this batch script to work.  Log Parser can be downloaded here.

The real benefit in running the EventLogUSB-Win7 batch script against multiple VSCs is that it allows you to recover USB connection and disconnection events that have since rolled off the current DriverFrameworks-UserMode/Operational event log.  This can be invaluable in cases where the length of time a certain device was connected to the system is important and the time frame of interest is prior to the earliest event in the current DriverFrameworks-UserMode/Operational event log.

Other Updates

In addition to the CompareDirectory and EventLogUSB-Win7 batch scripts, various user interface and general usability enhancements to VSC Toolset were made.  These include tips in the output of some commands (e.g. CompareDirectory) to help make the output easier to understand and a few help buttons added to the interface in some situations (depending on which command is specified in the Command drop-down box) to clarify exactly what a specific parameter is requesting.  The file system view, visible after clicking "Browse Shadow Copy", has also been improved to allow for sorting by file name or date by clicking the appropriate column header.

To ease the burden of finding all of the supporting tools you'll need to take full advantage of VSC Toolset, I've added the download links and any special requirements for each on the VSC Toolset page.  This information was previously scattered across multiple blog posts.

I'm always open to and appreciate feedback, including suggestions for improvement and bug reports.  You can download the latest version of VSC Toolset here.

**Update 02-19-14**
Corey Harrell's auto_rip has been integrated into VSC Toolset.  Version 20140216 includes this update.

Friday, February 7, 2014

USB Device Tracking Batch Script

Last month, I wrote about utilizing the Windows 7 Event Log in USB device tracking.  In my previous post, I mentioned automating the process using Microsoft's Log Parser, but didn't go into much detail regarding how to do so other than a couple of Log Parser queries.  This post introduces a batch script that can be used to quickly identify USB storage devices that have been connected to and disconnected from a Windows 7 system based on information available from the Windows Event Log, specifically the Microsoft-Windows-DriverFrameworks-UserMode/Operational event log.

The Log Parser query described in my previous post identifies the connection and disconnection events associated with a given device identifier, but is limited in that it requires the user to have knowledge of the USB device identifier and must be executed for each device identifier of interest.  In many cases, an examiner will not have knowledge of the device identifier(s) that should be targeted or may be interested in a listing of connection and disconnection events within a particular time period (regardless of the device connected).  This batch script accepts a Microsoft-Windows-DriverFrameworks-UserMode/Operational event log as input and parses the connection and disconnection events associated with each unique USB device identifier, based on the connection and disconnection Event IDs described in my previous post (i.e. 2003 for connect, 2100 for disconnect).

The batch script performs three main steps:
  1. Scans the event log and generates a list of device identifiers
  2. Removes duplicate device identifiers from the list compiled in Step 1
  3. Queries the event log for connection and disconnection events associated with each unique device identifier
It may seem odd at first to remove duplicate device identifiers in Step 2, but this important step eliminates the duplicate entries that would otherwise be found in the script output and allows for quicker execution of the script (as each device identifier will be queried only once within the event log).

Example usage of evtx-usb.bat
The script output is in CSV format and may look something similar to the screenshot below.  The output includes the type of event (connect or disconnect), the device identifier, the time of the event, and the LifetimeID associated with the USB device connection session.

Sample output of evtx-usb batch script
As you can see, the screenshot above details three separate connection sessions for two different USB devices.  We know there are two separate devices because of the different device identifiers and we know there are three separate connection sessions by comparing the LifetimeID values.  For a refresher on the LifetimeID value, see my previous post.

The output of the batch script allows an examiner to easily pair connection and disconnection events using the LifetimeID value as well as quickly determine which devices may have been connected to the system at the same time by identifying different devices with the same LifetimeID.  Since the script output is in CSV format, filtering and sorting is easily accomplished using a spreadsheet editor.

Since the batch script relies on Microsoft Log Parser, you will need to download Log Parser here and ensure LogParser.exe and LogParser.dll are both in the same directory as the batch file.

The script is available for download here.

Thursday, January 30, 2014

MS Word 2013 Reading Locations

Microsoft Office 2013 introduced a new feature that allows a user to continue reading or editing a document starting at the last point he or she was working.  This feature, referred to by some as "pick up where you left off", is a convenient way to jump to the location within a document that Word believes was being read or edited most recently before a file was closed.  After opening a document and being greeted with the prompt pictured above, I was curious as to where this information is being tracked.  After a bit of investigation, I located a set of registry subkeys specific to Office 2013 where this information is stored.

When a document in Word 2013 is closed, a registry subkey is created or updated in the "Software\Microsoft\Office\15.0\Word\Reading Locations" subkey of the current user's NTUSER.DAT.  The subkey created should be named something similar to "Document 0", "Document 1", "Document 2", etc., as the number appended to the name of each subkey is incremented by one when a new document is closed.  Each "Document #" subkey should contain 3 values that may be of interest to an examiner: "Datetime", "File Path", and "Position".  All three values are stored as null-terminated Unicode strings.

Screenshot of Reading Locations Subkey











Datetime Value
The Datetime value corresponds to the local date and time the file was last closed. This value data is displayed in the format YYYY-MM-DD, followed by a "T", then HH:MM.

File Path Value
The File Path value is the fully qualified file name.

Position Value
The Position value appears to store the positioning data used to place the cursor at the point in the document "where you left off".  It appears that the second number in this value data is used to denote the location within the document.  For example, if a file is opened for the first time and then closed again without scrolling down through the document, the Position value data should be "0 0".  If a file is opened and the user scrolls down a bit through the document before closing it, the Position value data may be something like "0 1500".  The second number in this value data appears to increase as the user scrolls through (i.e. reads/edits) the document.  Note that positioning of the cursor does not seem to have an impact on this value.  That is, the second field in this value data increases even if the cursor is never moved from the beginning of the document.

Forensic Implications

Fifty unique files (based on fully qualified file name) can be tracked in the Reading Locations subkeys.  Each time a document in Word 2013 is closed, regardless of the version of Word that created the file, a Reading Locations subkey should be added or updated.  It should be noted, however, that files accessed from a user's SkyDrive do not appear to be tracked in the Reading Locations subkey.  If the file referenced by the "File Path" value data of any subkey is opened and closed again, the corresponding value data is updated, however, the organization of the "Document #" subkeys remains unchanged (i.e. "Document 0" is not shifted to "Document 1", etc.).  Interestingly, it appears that when the 51st document is opened, the "Document 49" subkey is overwritten, leaving data from the other subkeys untouched.  This LIFO rotation may have some interesting effects on examination, as it lends itself to preserving more historical data while recent activity is more likely to be overwritten. 

Sunday, January 12, 2014

MS Excel 2013 Last Saved Location Metadata

The release of Microsoft Office 2013 granted the ability to save files in formats not previously available (such as "Strict OOXML"), but the default format remained the same as Office 2007 and 2010.  Despite the common file format, I've found that Microsoft Excel 2013 spreadsheets maintain additional metadata not available in earlier versions of Excel.  Specifically, it appears that the absolute path to the directory in which the spreadsheet was last saved is maintained by Excel 2013 spreadsheets.

I have not yet found a tool that presents the last saved location with other metadata from an Excel 2013 spreadsheet, but this information can easily be found by opening the "workbook.xml" file embedded in the parent spreadsheet.  Simply changing the file extension from "xlsx" to "zip" and using a zip-extraction utility to extract the contents of the spreadsheet is a quick way to gain access to the embedded files without requiring any specialized tools.

Workbook.xml contains information about the Excel file such as worksheet names, window height and width parameters, and a bit of other information.  For the most part, this XML file appears to be similar across files created using Excel 2007, 2010, and 2013, however, there is one key difference: the "x15ac:absPath" element.  The "x15ac:absPath" element is a child element of "mc:Choice" (which is a child element of "mc:AlternateContent") and contains an attribute called "url" that corresponds to the last saved location of the spreadsheet.

Workbook.xml file from Excel 2013
Information from the "url" attribute could be helpful in many cases, particularly those in which the previous location of a spreadsheet is significant.  For example, examining this metadata field in a spreadsheet copied to a USB device could allow the examiner to identify the previous directory in which the spreadsheet was saved (before it was copied to the USB device).  It's important to note, however, that resaving a 2013 spreadsheet using Excel 2007 or 2010 appears to remove the "x15ac:absPath" element.

If you know that a spreadsheet was created using Excel 2013 but are unable to find the last saved location metadata, it's possible that the spreadsheet was last saved in a version of Excel other than 2013.  This can be verified through the "fileVersion" element, which is the first child element of "workbook".  The "fileVersion" element includes an attribute called "lastEdited" and, according to Microsoft documentation, the "lastEdited" attribute "specifies the version of the application that last saved the workbook". Interestingly, the value specified in the "lastEdited" attribute is not consistent with the application version of Excel (i.e. 2007=12.x, 2010=14.x, etc.).  Instead, this value is a single-digit numeral corresponding to a particular version of Excel.  I've ran some quick tests using 2007, 2010, and 2013 and summarized the corresponding fileVersion values for each Excel version in the table below.

fileVersion Value to Excel Version Mapping
Importantly, Excel 2013 is aware of the last saved location metadata and will clear this information if the user elects to do so using Excel's built-in Document Inspector. Otherwise, this data should travel with the file until it is saved again, at which point this metadata will either be removed or updated (depending on the version of Excel that saved the file).

Excel 2013 Document Inspector identifies Last Saved Location Metadata

Thursday, January 2, 2014

The Windows 7 Event Log and USB Device Tracking

Recently, there have been a few blog posts discussing evidence found on a system when USB devices are connected and removed (Yogesh Khatri's blog series and Nicole Ibrahim's blog).  I've been meaning to release this post for a while and Yogesh and Nicole's posts have motivated me to do so.  Much of the conversation regarding USB device activity on a Windows system often surrounds the registry, but the Windows 7 Event Log can provide a wealth of information in addition to the registry. Utilizing the Event Log during USB device investigations has been mentioned in various other locations, including chapter 5 of Harlan Carvey's Windows Forensics Analysis 3/E (and recently in Yogesh Khatri's blog).  This post discusses both USB device connection and disconnection artifacts found in the Windows 7 Event Log, specifically the Microsoft-Windows-DriverFrameworks-UserMode/Operational log, and explores an interesting value that can be used to pair a device's connection event with its associated disconnection event.

Connection Event IDs

When a USB removable storage device is connected to a Windows 7 system, a number of event records should be generated in the Microsoft-Windows-DriverFrameworks-UserMode/Operational event log.  The records include those with Event ID 2003, 2004, 2005, 2010, 2100, 2105, and more.  Some of the generated event records contain identifying information about the USB device that was connected.  For example, when viewing an event record with Event ID 2003 using the Windows Event Viewer, the event information below is displayed.

Connection Event Record
A portion of the text formatting in the screenshot above above should look familiar to most, as it contains some of the same information about a USB device that can be found in the SYSTEM hive. Importantly, the device serial number ("000ECC0100087054") is stored in last portion of the event record's strings section. Combined with the record's TimeGenerated field, an examiner can derive the date and time that a USB device was connected to the machine.

Disconnection Event IDs

When a USB thumb drive is disconnected from a Windows 7 system, a few event records should be generated in the same event log as the connection events.  Records with Event ID 2100, 2102, and potentially more may be generated when a USB device is disconnected.  Variables such as whether there is another USB removable storage device still connected to the system at the time a USB device is disconnected can dictate which event records are generated and which are not.  Some records, however, appear to be more consistent.  For example, it appears that an event record with Event ID 2100 and the text "Received a Pnp or Power operation (27, 23) for device <deviceInfo>" is consistently generated when a USB removable storage device is disconnected from a system.  In addition, the same event record should contain the device's serial number/Windows unique identifier that can be mapped to a device.  An example of some of the information available from a disconnection event record with Event ID 2100 can be seen in the screenshot below.

Disconnection Event Record

LifetimeID Value

The LifetimeID value associated with a USB device's connection session is an interesting piece of information.  This GUID value is assigned to a UMDF (User Mode Driver Framework) host when a USB device is connected and should remain the same throughout the connection "lifetime" of the device.  In other words, an examiner should be able to match the LifetimeID written to a device's connection event records with the LifetimeID written to the device's disconnection event records in order to tie a particular disconnection event with its associated connection event.

This is simple enough when a single USB device is used, however, when multiple USB devices are used at once, they appear to all use the same UMDF host and are all assigned the same LifetimeID.  This means that a LifetimeID value cannot be tied to a single USB device, but it appears that it can be used to correlate device connections and disconnections on a per-session basis.

LifetimeID from Disconnection Event Record
Utilizing the LifetimeID associated with a device connection session can help in developing a timeline that, among other things, indicates the length of time a particular device was connected to the system.  In addition, the LifetimeID is useful in pairing a device's connection event with its corresponding disconnection event.  Since there may not be the same number of connection and disconnection events (e.g. a device is removed after the system has been powered down so no disconnection events are generated), the LifetimeID can help to make sense of various connections and disconnections and correctly pair the two together for a particular device.

In addition to being used to determine the length of a USB device's connection session via the Windows Event Log, the LifetimeID value may play an interesting and useful role in determining the time a USB device was last disconnected from the system, based on the LastWrite time of a registry subkey.  I'll forego this discussion for now since this post is focused on event records, but will revisit this topic later.

Automation

Automating the process of identifying connection and disconnection event records can really allow the power of utilizing the Windows Event Log in USB analysis to shine. While entirely possible, it would be a tedious process to manually analyze the Windows Event Log for USB connection/disconnection events.  Microsoft Log Parser is a great tool for processing the Event Log in this manner.  Given that event records associated with a device's connection and disconnection will contain identifying information as well as a timestamp, it's just a matter of isolating the event records associated with connection and disconnection and parsing portions of the strings section of the record.  For example, the Log Parser query below returns all event records with Event ID 2003 (connect) or 2100 (disconnect) as long as the device serial number/Windows unique identifier ("1372995DDDCB6185180CDB&0" in this case) is contained in the Strings portion of the event record and, in the case of a disconnection event, the text "27|23" is also in the Strings portion.
logparser -i EVT -o datagrid "SELECT EventID, TimeGenerated FROM Microsoft-Windows-DriverFrameworks-UserMode-Operational.evtx WHERE (EventID=2003 AND STRINGS Like '%1372995DDDCB6185180CDB&0%') OR (EventID=2100 AND STRINGS LIKE '%1372995DDDCB6185180CDB&0%27|23%')"   
Output of Log Parser query above
If you want to clean up the output and add a bit more information, you can use the Log Parser query below (replacing "1372995DDDCB6185180CDB&0" with the USB serial number/Windows unique identifier you're interested in).
logparser -i EVT -o datagrid "SELECT CASE EventID WHEN 2003 THEN 'Connect' WHEN 2100 THEN 'Disconnect' END As Event, TimeGenerated as Time, '1372995DDDCB6185180CDB&0' as DeviceIdentifier, EXTRACT_TOKEN(Strings,0,'|') as LifetimeID FROM Microsoft-Windows-DriverFrameworks-UserMode-Operational.evtx WHERE (EventID=2003 AND STRINGS Like '1372995DDDCB6185180CDB&0%') OR (EventID=2100 AND STRINGS LIKE '1372995DDDCB6185180CDB&0%27|23%')"
Output of Log Parser query above
As you can see, Log Parser dramatically reduces the leg work involved in analyzing event records for USB connection and disconnection events.  Moreover, Log Parser queries can easily be incorporated into a batch script that allows the examiner to input the device serial number he or she is interested in to quickly identify the connection and disconnection events associated with the device.  The LifetimeID value can then be used match associated connection and disconnection events.

As with other event logs, event records in the Microsoft-Windows-DriverFrameworks-UserMode/Operational event log eventually roll over, leaving the examiner with a limit on how far back in time he or she can go.  However, utilizing VSCs can allow an examiner to squeeze a bit more out of this approach and ultimately build a very telling history of USB device connection and disconnection events.  

Monday, September 9, 2013

Windows 8 and 8.1: Search Charm History

The upcoming release of Windows 8.1 offers new features that will add to and/or modify the forensic artifacts available for examination.  One of these additions is the "Search Everywhere" feature that allows a user to search his or her files, settings, apps, and even the Internet at the same time.  In contrast, Windows 8 restricts a user to searching within a single category of data at a time (files, settings, apps).  The new search feature of 8.1 introduces artifacts not available in Windows 8 and provides examiners with another source of search charm data.  This post will discuss artifacts available in both Windows 8 and 8.1 as a result of the user conducting searches via the Windows search charm.

In order to utilize the "Search Everywhere" feature of Windows 8.1, the user must run a search using the Windows search charm, a feature introduced with Windows 8. This is not the same as conducting a search using Windows Explorer and leaves a different set of artifacts.  

Windows 8.1 Search Charm
Windows 8 Search Charm










When a user runs a search using the search charm in Windows 8, specifically selecting "Files" as the search category, the search term is added as a value to an MRU list (maintained by an MRUListEx value) in the user's NTUSER.DAT under \Software\Microsoft\Windows\CurrentVersion\Explorer\SearchHistory\ Microsoft.Windows.FileSearchApp.  If the "Settings" or "Apps" category is selected, the search term does not appear to be added as a value to the MRU list (nor is a separate subkey created in the SearchHistory key).

Windows 8.1 also utilizes the SearchHistory key to maintain an MRU list of search terms, but within the SearchHistory\EXPLORER.EXE subkey instead.  Additionally, it appears that all search terms executed using the search charm are stored as a value here (as opposed to only the terms executed against the "Files" category).  An MRUListEx value is used to maintain the list here as well and the search term itself is stored in Unicode as type REG_BINARY.

In addition to the SearchHistory subkey, it appears that Windows 8.1 maintains another set of artifacts in the form of LNK files in the user's AppData\Local\Microsoft\Windows\ ConnectedSearch\History directory.  Interestingly, the LNK files associated with the search charm history that I've examined consist of only the LNK header and a shell item ID list containing the search term.  This means that if your tool does not parse shell item ID lists, it will not extract the search term from these files.  The LNK files I've examined that are associated with the search charm do not contain embedded FILETIME timestamps in the LNK header or DOSDate timestamps in the shell item ID list.  Further, if the user runs the same search term at a later date, there appears to be no change to the file content or file system timestamps of the LNK file.  This means that the file system timestamps associated with these files can only be used to identify the first time a particular search was conducted.

The search charm LNK files could be quite useful during an examination, despite the fact that the search terms are also stored in the user's NTUSER.DAT.  For example, these files can help determine a specific time that each search term was used, provide additional artifacts to support that a particular search term was/wasn't used, and may be useful if the user has taken steps to remove his or her search charm history.  When the search charm history is cleared (via search & apps settings), the entire SearchHistory subkey and the LNK files in the ConnectedSearch\History directory are deleted.  The existence of these LNK files provides another possible avenue to recover previously used search terms.  One thing to note with respect to these files is that they are likely to be resident, given the fact that they contain only the LNK header and a small shell item ID list.

The testing I've conducted with regard to the Windows 8 and 8.1 search charm history has been with the default settings.  The Preview version of Windows 8.1 Professional was used for all testing related to 8.1.  At the time of this writing, the option to search the Internet using Bing is not a default option and thus was not tested.  It will be interesting to see if/how this option changes the artifacts available to an examiner.  At any rate, the Windows search charm, both with and without the "Search Everywhere" feature, provides additional forensic artifacts to help examiners piece together user activity in a Windows environment.