Difference between pages "THE FARMER'S BOOT CD" and "Forensic Live CD issues"

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[http://www.forensicbootcd.com/ THE FARMER'S BOOT CD (FBCD)] is a unique Linux boot CD.  Taking a different approach than other [[Live CDs]], this CD was designed and optimized for previewing systems before acquiring.  THE FARMER'S BOOT CD contains a number of programs forensic practitioners can utilize to preview both Windows and Linux systems in a forensically sound manner.  Developed by Thomas Rude ('farmerdude').
+
== The problem ==
  
 +
[[Live CD|Forensic Live CDs]] are widely used during computer forensic investigations. Currently, many vendors of such Live CD distributions spread false claims that their distributions "do not touch anything", "write protect everything" and so on. Unfortunately, community-developed distributions are no exception here. Finally, it turns out that many Linux-based forensic Live CDs are not tested properly and there are no suitable test cases published.
  
== Preview Capabilities ==
+
== Another side of the problem ==
  
THE FARMER'S BOOT CD has been designed for previewing both Windows and Linux systems.  On-site previews before acquisitions is an emerging trend in the U.S.A. due to legal and technological reasons.
+
Another side of the problem of insufficient testing of forensic Live CDs is that many users do not know what happens "under the hood" of the provided operating system and cannot adequately test them.
  
Below is a short list of what can be accomplished in a simple GUI on this CD;
+
=== Example ===
  
- Mount file systems read-only, including journalled file system types
+
For example, [http://forensiccop.blogspot.com/2009/10/forensic-cop-journal-13-2009.html ''Forensic Cop Journal'' (Volume 1(3), Oct 2009)] describes a test case when an Ext3 file system was mounted using "-o ro" mount flag as a way to write protect the data. The article says that all tests were successful (i.e. no data modification was found after unmounting the file system), but it is known that damaged (i.e not properly unmounted) Ext3 file systems cannot be write protected using only "-o ro" mount flags (write access will be enabled during file system recovery).
- Obtain a list of deleted files for ext2, FAT12/16/32, and NTFS file system types
+
- Undelete deleted files from NTFS file systems
+
- Obtain both E-mail and URL addresses from the Windows "pagefile.sys" file
+
- Read the Recycle Bin INFO2 records
+
- Read Windows event log files (AppEvent.Evt, SecEvent.Evt, SysEvent.Evt)
+
- Read many log files from Linux systems (shell histories, system logs, security logs, accounting logs, etc.)
+
- Obtain file system metainformation (creation date, last mount and write date, version, label, UUID, etc.)
+
- Parse Internet cache files from IE, Mozilla, and Opera, pulling cookies and histories
+
- Catalog target file system, selecting files of interest by extension or header
+
- Convert date/time between UNIX 32bit, UNIX hex, human readable, Windows 64bit, and Windows hex
+
- Generate thumbnails for all graphics in fully qualified path filename
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- Obtain drive information (serial number, make/model, firmware, HPA status, etc.)
+
- Obtain system BIOS table information (serial numbers, dates, UUIDs, etc.)
+
- Obtain system hardware catalog
+
- Double-clicking on most common file types opens them (Documents, Graphics, Presentations, Movies, Audio, etc.)
+
  
 +
And the question is: will many users test damaged Ext3 file system (together with testing the clean one) when validating their favourite forensic Live CD distribution? My answer is "no", because many users are unaware of such traits.
  
== Links ==
+
== Problems ==
  
[http://www.forensicbootcd.com/ THE FARMER'S BOOT CD Page] Main Page for THE FARMER'S BOOT CD (FBCD).
+
Each problem is followed by a list of distributions affected (currently this list is not up-to-date).
  
[http://www.forensicbootcd.com/site/view.html THE FARMER'S BOOT CD screen shots] Screen Shots for Delve Preview Program on the FBCD.
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=== Journaling file system updates ===
  
[http://www.forensicfocus.com/farmers-boot-cd Preview Data in Under Twenty Minutes] Paper on previewing data quickly at http://www.forensicfocus.com
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When mounting (and unmounting) several journaling file systems with only "-o ro" mount flag a different number of data writes may occur. Here is a list of such file systems:
  
[[category:Forensic Utilities]]
+
{| class="wikitable" border="1"
 +
|-
 +
!  File system
 +
!  When data writes happen
 +
!  Notes
 +
|-
 +
|  Ext3
 +
|  File system requires journal recovery
 +
|  To disable recovery: use "noload" flag, or use "ro,loop" flags, or use "ext2" file system type
 +
|-
 +
|  Ext4
 +
|  File system requires journal recovery
 +
|  To disable recovery: use "noload" flag, or use "ro,loop" flags, or use "ext2" file system type
 +
|-
 +
|  ReiserFS
 +
|  File system has unfinished transactions
 +
|  "nolog" flag does not work (see ''man mount''). To disable journal updates: use "ro,loop" flags
 +
|-
 +
|  XFS
 +
|  Always (when unmounting)
 +
|  "norecovery" flag does not help (fixed in recent 2.6 kernels). To disable data writes: use "ro,loop" flags.
 +
|}
 +
 
 +
Incorrect mount flags can be used to mount file systems on evidentiary media during the boot process or during the file system preview process. As described above, this may result in data writes to evidentiary media. For example, several Ubuntu-based forensic Live CD distributions mount and recover damaged Ext3/4 file systems on fixed media (e.g. hard drives) during execution of [http://en.wikipedia.org/wiki/Initrd ''initrd''] scripts (these scripts mount every supported file system type on every supported media type using only "-o ro" flag in order to find a root file system image).
 +
 
 +
[[Image:ext3 recovery.png|thumb|right|[[Helix3]]: damaged Ext3 recovery during the boot]]
 +
 
 +
List of distributions that recover Ext3 (and sometimes Ext4) file systems during the boot:
 +
 
 +
{| class="wikitable" border="1"
 +
|-
 +
!  Distribution
 +
!  Version
 +
|-
 +
|  Helix3
 +
|  2009R1
 +
|-
 +
|  SMART Linux (Ubuntu)
 +
|  2010-01-20
 +
|-
 +
|  FCCU GNU/Linux Forensic Boot CD
 +
|  12.1
 +
|-
 +
|  SPADA
 +
|  4
 +
|-
 +
|  DEFT Linux
 +
|  7
 +
|}
 +
 
 +
=== Orphan inodes deletion ===
 +
 
 +
When mounting Ext3/4 file systems all orphan inodes are removed, even if "-o ro" mount flag was specified. Currently, there is no specific mount option to disable orphan inodes deletion. The only solution here is to use "-o ro,loop" flags.
 +
 
 +
=== Root file system spoofing ===
 +
 
 +
''See also: [[Early userspace | early userspace]]''
 +
 
 +
Most Ubuntu-based forensic Live CD distributions use Casper (a set of scripts used to complete initialization process during early stage of boot). Casper is responsible for searching for a root file system (typically, an image of live environment) on all supported devices (because a bootloader does not pass any information about device used for booting to the kernel), mounting it and executing ''/sbin/init'' program on a mounted root file system that will continue the boot process. Unfortunately, Casper was not designed to meet computer forensics requirements and is responsible for damaged Ext3/4 file systems recovery during the boot (see above) and root file system spoofing.
 +
 
 +
[[Image:Grml.png|thumb|right|[[grml]] mounted root file system from the [[hard drive]]]]
 +
 
 +
Currently, Casper may select fake root file system image on evidentiary media (e.g. [[Hard Drive|HDD]]), because there are no authenticity checks performed (except optional UUID check for a possible live file system), and this fake root file system image may be used to execute malicious code during the boot with root privileges. Knoppix-based forensic Live CD distributions are vulnerable to the same attack.
 +
 
 +
List of Ubuntu-based distributions that allow root file system spoofing:
 +
 
 +
{| class="wikitable" border="1"
 +
|-
 +
!  Distribution
 +
!  Version
 +
|-
 +
|  Helix3
 +
|  2009R1
 +
|-
 +
|  Helix3 Pro
 +
|  2009R3
 +
|-
 +
|  CAINE
 +
|  1.5
 +
|-
 +
|  DEFT Linux
 +
|  5
 +
|-
 +
|  Raptor
 +
|  2.0
 +
|-
 +
|  BackTrack
 +
|  4
 +
|-
 +
|  SMART Linux (Ubuntu)
 +
|  2010-01-20
 +
|-
 +
|  FCCU GNU/Linux Forensic Boot CD
 +
|  12.1
 +
|}
 +
 
 +
Vulnerable Knoppix-based distributions include: SPADA, LinEn Boot CD, BitFlare.
 +
 
 +
[http://anti-forensics.ru/ Anti-Forensics.Ru project] [http://digitalcorpora.org/corp/images/aor/ released several ISO 9660 images] used to test various Linux Live CD distributions for root file system spoofing (description for all images is [http://anti-forensics.ru/casper/ here]).
 +
 
 +
=== Swap space activation ===
 +
 
 +
''Feel free to add information about swap space activation during the boot in some distributions''
 +
 
 +
=== Incorrect mount policy ===
 +
 
 +
==== rebuildfstab and scanpartitions scripts ====
 +
 
 +
Several forensic Linux Live CD distributions (Helix3 2009R1, Helix3 Pro 2009R3, old versions of CAINE, old versions of grml) use rebuildfstab and scanpartition scripts to create entries for attached devices in ''/etc/fstab''. Some versions of these scripts use wrong wildcards while searching for available block devices (''/dev/?d?'' instead of ''/dev/?d*''), this results in missing several "exotic" devices (like /dev/sdad, /dev/sdad1, etc) and in data writes when mounting them (because fstab lacks of read-only mount options for these devices).
 +
 
 +
=== Incorrect write-blocking approach ===
 +
 
 +
Some forensic Linux Live CD distributions rely on [[hdparm]] and [[blockdev]] programs to mount file systems in read-only mode (by setting the underlying block device to read-only mode). Unfortunately, setting the block device to read-only mode does not guarantee that [http://archives.free.net.ph/message/20090721.105120.99250e3f.en.html no write commands will be passed to the drive].
 +
 
 +
== External links ==
 +
 
 +
* [http://www.computer-forensics-lab.org/pdf/Linux_for_computer_forensic_investigators_2.pdf Linux for computer forensic investigators: problems of booting trusted operating system]
 +
* [http://www.computer-forensics-lab.org/pdf/Linux_for_computer_forensic_investigators.pdf Linux for computer forensic investigators: «pitfalls» of mounting file systems]
 +
 
 +
[[Category:Live CD]]

Revision as of 17:24, 19 May 2014

The problem

Forensic Live CDs are widely used during computer forensic investigations. Currently, many vendors of such Live CD distributions spread false claims that their distributions "do not touch anything", "write protect everything" and so on. Unfortunately, community-developed distributions are no exception here. Finally, it turns out that many Linux-based forensic Live CDs are not tested properly and there are no suitable test cases published.

Another side of the problem

Another side of the problem of insufficient testing of forensic Live CDs is that many users do not know what happens "under the hood" of the provided operating system and cannot adequately test them.

Example

For example, Forensic Cop Journal (Volume 1(3), Oct 2009) describes a test case when an Ext3 file system was mounted using "-o ro" mount flag as a way to write protect the data. The article says that all tests were successful (i.e. no data modification was found after unmounting the file system), but it is known that damaged (i.e not properly unmounted) Ext3 file systems cannot be write protected using only "-o ro" mount flags (write access will be enabled during file system recovery).

And the question is: will many users test damaged Ext3 file system (together with testing the clean one) when validating their favourite forensic Live CD distribution? My answer is "no", because many users are unaware of such traits.

Problems

Each problem is followed by a list of distributions affected (currently this list is not up-to-date).

Journaling file system updates

When mounting (and unmounting) several journaling file systems with only "-o ro" mount flag a different number of data writes may occur. Here is a list of such file systems:

File system When data writes happen Notes
Ext3 File system requires journal recovery To disable recovery: use "noload" flag, or use "ro,loop" flags, or use "ext2" file system type
Ext4 File system requires journal recovery To disable recovery: use "noload" flag, or use "ro,loop" flags, or use "ext2" file system type
ReiserFS File system has unfinished transactions "nolog" flag does not work (see man mount). To disable journal updates: use "ro,loop" flags
XFS Always (when unmounting) "norecovery" flag does not help (fixed in recent 2.6 kernels). To disable data writes: use "ro,loop" flags.

Incorrect mount flags can be used to mount file systems on evidentiary media during the boot process or during the file system preview process. As described above, this may result in data writes to evidentiary media. For example, several Ubuntu-based forensic Live CD distributions mount and recover damaged Ext3/4 file systems on fixed media (e.g. hard drives) during execution of initrd scripts (these scripts mount every supported file system type on every supported media type using only "-o ro" flag in order to find a root file system image).

Helix3: damaged Ext3 recovery during the boot

List of distributions that recover Ext3 (and sometimes Ext4) file systems during the boot:

Distribution Version
Helix3 2009R1
SMART Linux (Ubuntu) 2010-01-20
FCCU GNU/Linux Forensic Boot CD 12.1
SPADA 4
DEFT Linux 7

Orphan inodes deletion

When mounting Ext3/4 file systems all orphan inodes are removed, even if "-o ro" mount flag was specified. Currently, there is no specific mount option to disable orphan inodes deletion. The only solution here is to use "-o ro,loop" flags.

Root file system spoofing

See also: early userspace

Most Ubuntu-based forensic Live CD distributions use Casper (a set of scripts used to complete initialization process during early stage of boot). Casper is responsible for searching for a root file system (typically, an image of live environment) on all supported devices (because a bootloader does not pass any information about device used for booting to the kernel), mounting it and executing /sbin/init program on a mounted root file system that will continue the boot process. Unfortunately, Casper was not designed to meet computer forensics requirements and is responsible for damaged Ext3/4 file systems recovery during the boot (see above) and root file system spoofing.

grml mounted root file system from the hard drive

Currently, Casper may select fake root file system image on evidentiary media (e.g. HDD), because there are no authenticity checks performed (except optional UUID check for a possible live file system), and this fake root file system image may be used to execute malicious code during the boot with root privileges. Knoppix-based forensic Live CD distributions are vulnerable to the same attack.

List of Ubuntu-based distributions that allow root file system spoofing:

Distribution Version
Helix3 2009R1
Helix3 Pro 2009R3
CAINE 1.5
DEFT Linux 5
Raptor 2.0
BackTrack 4
SMART Linux (Ubuntu) 2010-01-20
FCCU GNU/Linux Forensic Boot CD 12.1

Vulnerable Knoppix-based distributions include: SPADA, LinEn Boot CD, BitFlare.

Anti-Forensics.Ru project released several ISO 9660 images used to test various Linux Live CD distributions for root file system spoofing (description for all images is here).

Swap space activation

Feel free to add information about swap space activation during the boot in some distributions

Incorrect mount policy

rebuildfstab and scanpartitions scripts

Several forensic Linux Live CD distributions (Helix3 2009R1, Helix3 Pro 2009R3, old versions of CAINE, old versions of grml) use rebuildfstab and scanpartition scripts to create entries for attached devices in /etc/fstab. Some versions of these scripts use wrong wildcards while searching for available block devices (/dev/?d? instead of /dev/?d*), this results in missing several "exotic" devices (like /dev/sdad, /dev/sdad1, etc) and in data writes when mounting them (because fstab lacks of read-only mount options for these devices).

Incorrect write-blocking approach

Some forensic Linux Live CD distributions rely on hdparm and blockdev programs to mount file systems in read-only mode (by setting the underlying block device to read-only mode). Unfortunately, setting the block device to read-only mode does not guarantee that no write commands will be passed to the drive.

External links