Thursday, July 10, 2014

Identifying Android Device Owners

I work in a college town.  That means lots of unsecured electronics.  Lots of unsecured electronics means lots of thefts and 'misplaced'--"I'm not as think as you drunk I am!"--devices.

I've seen a trend in recovered stolen devices over the past few years: the bad guys are rapidly restoring devices to factory settings to prevent them from being tracked by the owner or law enforcement.  That leaves me with a problem, though: how do I determine the owner of a device that has been restored?   Allocated data that could show ownership is deleted upon a system restore.  Since, I've discussed other devices in the past, today I'll focus on Androids.

Dispossessed Androids

I've had uneven success with Androids in the past.  This may be due in part to the fact that I've not always know what to look for.  But I received two more such devices this week and decided to apply myself, once again, to the problem of identifying the owners.  Since I became an Android owner myself over the past 18 mos, I had a device with known data with which to experiment.

Android Recovery

Nearly all data that contains identifying information is stored in the 'data' partition.  When a device is restored or 'wiped' through the Android recovery system, personal data is removed.  This process is usually quite fast, which leads me to believe that 'wiping' user data is a simple delete in most cases.   There are custom recoveries where this might not be true, but a study of unallocated data in a wiped device reveals a rich data field. 

In Unix-like systems, physical storage devices are attached to the operating system through special files (drivers) called device nodes.  These nodes provide raw access to devices and their partitions.  Thus, if a device node, also referred to as a block device, is addressed, all content is accessible, allocated and unallocated alike.  Block devices can be thought of and addressed by software tools as files.  To access block devices, however, one must have root access to the operating system.  I will not be discussing the various ways to achieve root access to an Android device in this article, however.  I will continue on the assumption that the device has been rooted.

Tinkering under the hood

Access to a running Android device is done through the Android Debug Bridge (adb).  In a stock recovery or Android operating system, adb provides shell user access to the file system.  The shell user has limited access to the device and commands, but the root user has full access.  Root access, when not immediately granted through the adb shell command, is obtained by the su command.
shell@device:/ $
shell@device:/ $ su
root@device:/ # 
Block device files are found in the /dev/block directory. The file representing the entire NAND flash is the /dev/block/mmcblk0 file. Partitions are represented as /dev/block/mmcblk0p1, /dev/block/mmcblk0p2, etc. A paritial directory listing in my device, for example, is:
We could address the entire memory storage device through mmcblk0, but it would be more efficient to address just the data partition.  But which of these is the data partition?  There are several ways to figure this out, and while not all of the following methods will work on every device, at least one should.
  1. If the data partition is mounted, such as would occur in a rooted and running operating system, simply issue the mount command:

    # mount | grep /data
    /dev/block/mmcblk0p25 on /data type ext4 (ro,relatime,barrier=1,data=ordered)

  2. Check the contents of the /etc/fstab file:

    # cat /etc/fstab
    /dev/block/mmcblk0p24 /system ext4 rw
    /dev/block/mmcblk0p25 /data ext4 rw
    /dev/block/mmcblk0p26 /cache ext4 rw
    /dev/block/mmcblk1p1 /sdcard vfat rw
    /dev/block/mmcblk0p28 /emmc vfat rw
    /dev/block/mmcblk1p2 /sd-ext  rw
    /dev/block/mmcblk0p21 /efs ext4 rw

  3. Look for the 'by-name' directory somewhere in the /dev/block/platform subtree:

    # ls /dev/block/platform/msm_sdcc.1/by-name/ -l | grep data  
    lrwxrwxrwx root root 2014-06-24 03:10 data -> /dev/block/mmcblk0p25

    Note that the 'by-name' data file is actually link to the /dev/block/mmcblk0p25.

Getting to the Point

Ok, we know how to identify and address the data partition, but for what do we search?  After some experimentation with my own device, it appears that a very profitable target are application license files. The com.application.vending domain contains application licensing information.  On my device, I found 16 binary files in the /data/data/ directory that appear to be application licenses from applications downloaded from the Google Play store.  While I could not find specific information about these files, a reading of Android developer page for licensing applications suggests this files purpose.  Importantly all contained my username in the form of:
Crafting a search of the data partition of a restored device with this knowledge is fairly simple:
# strings mmcblk0p25 | egrep -o 'account="?.{1,25}"?'
Note: the strings and egrep commands are available through busybox which can be temporarily installed to the /dev/ folder (a temporary file system in RAM) if not already present in your environment using the adb push busybox /dev/ command.
Output of the search can be sorted and counted using a sort | uniq pipeline for clean results.
# strings -td mmcblk0.raw | \egrep -o 'account="?.{1,25}"?' | \sort | uniq -c | sort -n
970 account=""
2161 account=""
From the output, we can see there have been two user accounts.  Did they both exist on the system at the same time.  Has the device changed hands?  We don't know, but we have two email addresses for contacting people who might know!

Tuesday, May 6, 2014

Searching for Searches

In a recent examination of smart phone content, it became necessary to know the personal interests of the device's owner.  You can browse internet and app history, but that can be extensive to review every URLs to every clicked link and served page.  To get directly to the point, I decided to search for his browser/app search query history.  I was hoping to craft a regular expression (or several) that would assist in giving me a good idea of the person's interests.

I studied some top search engine results and reviewed some browser history and crafted the following GNU extended regular expression:


This search, run against strings output of files, found search queries for Google, Yahoo!, Bing, Ask, Aol, Faceboot, YouTube, Vimeo and some x-rated sites as well as app content such as Twitter.  Search results appear (depending on what you feed and how you configure GNU grep) similar to:

An added benefit to this expression is that it also hits on additional page results, Google images page refreshes, etc.   With little command line wiz-bangery, it's even possible to sort and count the results to get a histogram of searches:

strings History.plist | egrep -o '[?&](k|p|q|query)=[a-zA-Z0-9+_%-]+' | sed 's/.*=//' | sort | uniq -c | sort -nr

I'll explain the command above:
  1. strings History.plist # extract ascii strings from the iPhone Safari History.plist
  2. egrep -o '[?&](k|p|q|query)=[a-zA-Z0-9+_%-]+' # grep for the regular expression described above
  3. sed 's/.*=//' # strip off the query tag at the front of the user typed query
  4. sort # sort the results alphabetically
  5. uniq -c  # count the matching lines
  6. sort -nr # reverse sort, placing the most frequent query terms first.
Results of the command look similar to the following:

   21    I+search+for+this+a+lot
   11    this%20one%20a%20little%less
    2    why+would+anyone+read+linux+sleuthing
    1    testing%20one%20two

The expression could be run against all logical files in a device and against unallocated space, if applicable.  I only demonstrate it using the History.plist because it's easy illustrate.

I post this short article both because I want to remember this regular expression (the whole reason for my blog in the first place) and to solicit favorite search box/engine regular expressions you might have. Please share them in a comment if you get a chance.  Happy searching!

Tuesday, April 22, 2014

Finding Serial Numbers on Locked iPhones

Apple iDevices have their serial number engraved on the back, right? So why the article? Because it's not true of newer devices like the iPhone 5, 5s, and 5c. Also, original cases can be replaced and serial numbers obliterated through unprotected use or deliberate act. Now I have your attention again, I hope.

Getting the Message

I've written in the past about the libimobiledevice library and it's utilities.  One, which is quite handy for gathering device information is ideviceinfo.  It provides information such as the device description (color), device class (iPhone, iPod, iPad), device name, etc.  When the device is unlocked, you can retrieve the serial number, as well.  Basically, you retrieve the contents of the Info.plist.

But ideviceinfo is not so informative with a locked device.  In fact, it won't show you any output unless you use the -s simple option.  While you can obtain some information, such as the description, class, name, UDID (unique identifier), and Mac address, you can't display the serial number.  But never fear, there is a way...

Linux has a system log that tracks systems events, included the plugging and unplugging of devices. The system log can be dumped the the terminal with the dmesg command.  Run by itself, you dump the entire log and it's quite a lot of information to sift through, though in truth what you want will be found at or near the end of the log.  You can shorten the output to the content you need with

$ dmesg syslog

But an even niftier trick is to set up your system to display the log as it is created and watch the output:

$ tail -f /var/log/syslog

This will display the last 10 lines of the system log and the "follow" it until you cancel with ctrl-c. Now you can hotplug your iDevice and watch the data that the system log records about the device. Unfortunately, you will see that it displays the device UDID and not the serial number in the "SerialNumber" field for a locked iDevice.

Recovering the Serial Number

The serial number is recoverable in Recovery Mode, however.  Pressing and holding the hardware power button brings up the software power off slide button.  Power off the device, and then replug it into your Linux box while holding the hardware home button.  The device will boot into recovery mode.  Now check your syslog with either of the two methods discussed above.  Two serial numbers are displayed in the syslog after the product (iPhone, etc) and manufacturer (Apple) are listed.  The first is the UDID, but the second includes several key:value pairs, one of which is the device serial number (key SRNM).  

When you are done collecting the device data revealed in the syslog, reboot it, if required, by pressing and holding the power button approximately 10 seconds until the recovery screen goes blank.  The device will then reboot into the operating system, probably feeling very ashamed of itself for revealing its secrets so readily.