Stop, Drop and File Carve
Last Updated: 2013-08-26 17:27:59 UTC
by Alex Stanford (Version: 1)
This is a "guest diary" submitted by Tom Webb. We will gladly forward any responses or please use our comment/forum section to comment publically. Tom is currently enrolled in the SANS Masters Program.
Recently, a friend of mine had a USB drive "die on him" and he wanted me to look at it. He needed to recover PDF, DOC and PPT files on the drive. Fortunately, this drive did not appear to be damaged and I was able to access the physical disk but not the partition.
For a Linux forensics distro to complete the project below, the SANS SIFT works great http://computer-forensics.sans.org/community/downloads.
1. Image the drive
When doing forensic drive analysis you should always make a copy of the drive before you start analysis on the disk image and not the original. Using dcfldd for Linux or FTK Imager Lite for Windows will do the trick. Check the output of dmesg to determine the device ID when plugging in the USB to your Linux VM.
#dmesg sd 32:33:0:0: [sdb] 4324088 512-byte hardware sectors (4043 MB)
Now that we have determined the physical device ID, lets output the file to /tmp/Broken-usb.001
#dcfldd bs=512 if=/dev/sdb of=/tmp/Broken-USB.001 conv=noerror,sync hash=md5 md5log=md5.txt
2. Troubleshoot the issue
Using the file command should show the partition information, but it does not.
# file Broken-USB.001 Broken-USB.001: data
MMLS results should also show us partition information, but again it doesn’t.
# mmls Broken-USB.001 Cannot determine partition type
Lets dump the start of the drive in hex and see if the drive is completely blank.
# xxd -l 1000 Broken-USB.001 0000000: 0600 0077 6562 6220 2020 2020 2020 2020 ..webb 0000010: 2020 2020 2020 2020 2020 2020 2020 2020 0000020: 2020 2020 2020 2020 2020 2020 2020 2020 0000030: 2020 2020 2020 2006 0000 0000 0077 0065 ......w.e 0000040: 0062 0062 0020 0020 0020 0020 0020 0020 .b.b. . . . . .
The drive does appear to have at least some data, but not a valid partition. It should be possible to pull files from the disk image.
3. Determine what you want to recover
Many file types have specific headers and footers when the file is created. We can use this to our advantage and search for these specific hex values on disk. Foremost is a tool that will use this technique for detecting file types.
The command below takes the input file (USB.001) and outputs to (/tmp/dump). If you want to specify just a few file types use the –t option, if not default is all.
foremost -v -i Broken-USB.001 -o /tmp/dump
4. Review Files
Foremost will create a bunch of folders and each should contain files. Some file should be complete, but other will likely be partial or corrupted.
Aug 26th 2013
9 years ago
For other distros, including CentOS, use http://www.sleuthkit.org/sleuthkit/download.php or use the SIFT referenced above.
Aug 27th 2013
9 years ago
If you want to find the location of various tools - especially the documentation, source code etc. there is an excellent website called http://www.google.com which is great for this.
Hope this helps,
Aug 28th 2013
9 years ago