Monthly Archives: August 2014

Intelligence driven Incident Response

killchainBack in March 2011, Eric Hutchins, Michael Cloppert and Dr. Rohan Amin from Lockheed Martin (US Gov defense contractor) released a paper named Intelligence Driven Computer Network Defense Informed by Analysis of Adversary Campaigns and Intrusion Kill Chains. This was a great contribution to the IT security community because it describes a novel way to deal with intrusions. They claim that current tools and models that deal with intrusions need to evolve mainly due to two things. First network defense tools focus on the vulnerability component of the risk instead of the threat. Second the traditional way of doing incident response happens after a successful intrusion.  To solve this problem they propose a model that leverages an understanding about the tools and techniques used by the attackers creating intelligence that is then used to decrease the likelihood success of an intrusion.  In order to understanding the threat actors , their tools and techniques they adopted models and terms that have origins in the US military. Essentially they propose to maps the steps taken by attackers during an intrusion. These steps are then intersected with a chain of events with the goal to detect, mitigate and respond to intrusions based on the knowledge of the threat using indicators, patterns and behaviors that are conducted during the course of action of the intrusion.

To map the attackers activity the authors propose an intelligence gathering element called indicator that is divided in three types:

  • Atomic – Atomic indicators are attributes relevant in the context of the intrusion and cannot be further divided into smaller parts. Examples include IP addresses, email addresses, DNS names.
  • Computed – Computed indicators are digital representation of data pertinent to the intrusion or patterns indentified with regular expressions. Examples include hashes from malicious files,  regular expressions used on IDS.
  • Behavioral – Behavioral indicators are a combination of atomic and computed indicators trough some kind of logic that outline a summary of the attackers tools and techniques. An example is well described by Mike Cloppert: “Bad guy 1 likes to use IP addresses in West Hackistan to relay email through East Hackistan and target our sales folks with trojaned word documents that discuss our upcoming benefits enrollment, which drops backdoors that communicate to A.B.C.D.’ Here we see a combination of computed indicators (Geolocation of IP addresses, MS Word attachments determined by magic number, base64 encoded in email attachments) , behaviors (targets sales force), and atomic indicators (A.B.C.D C2)”

The phases to map the attacker activity are based on US DoD information operations doctrine with its origins in the field manual 100-6 from the Department of the Army. This systematic process evolved over the years and is also described in the Air Force Doctrine Document 2-1.9 8 June 2006 as kill chain and referred in military language as dynamic targeting process F2T2EA (Find, Fix, Track, Target, Engage, and Assess) or F3EAD (Find, Fix, Finish, Exploit, Analyze and Disseminate). The authors expanded this concept and presented a new kill chain model to deal with intrusions. The 7 phases of the cyber kill chain are:

  • Reconnaissance : Research, identification and selection of targets, often represented as crawling Internet websites such as conference proceedings and mailing lists for email addresses, social relationships, or information on specific technologies.
  •  Weaponization : Coupling a remote access trojan with an exploit into a deliverable payload, typically by means of an automated tool (weaponizer). Increasingly, client applications data files such as Adobe PDF or Microsoft Office documents serve as the weaponized deliverable.
  •  Delivery : Transmission of the weapon to the targeted environment using vectors like email attachments, websites, and USB removable media.
  •  Exploitation : After the weapon is delivered to victim host, exploitation triggers intruders’ code. Most often, exploitation targets an application or operating system vulnerability, but it could also more simple exploit the users themselves or leverage an operating system feature that auto-executes.
  •  Installation : Installation of a remote access trojan or backdoor on the victim system allows the adversary to maintain persistence inside the environment.
  •  Command and Control (C2) : Typically, compromised hosts must beacon outbound to an Internet controller server to establish a C2 channel.
  •  Actions on Objectives : Only now, after progressing through the first six phases, can intruders take actions to achieve their original objectives. Typically this objective is data exfiltration which involves collecting, encrypting and extracting information from the victim environment. Alternatively, the intruders may only desire access to the initial victim box for use as a hop point to compromise additional systems and move laterally inside the network.

Then these steps are used to produce a course of action matrix that is modeled against a system that is used, once again, in military language as offensive information operations with the aim to  detect, deny, disrupt, degrade, deceive and destroy. The goal is to create a plan that degrades the attacker ability to perform his steps and forcing him to be reactive by interfering with the chain of events. This will slow the attackers movements, disrupt their decision cycles and will increase the costs to be successful.  The following picture taken from the original paper illustrates the course of action matrix.



This model is a novel way to deal with intrusions by moving from the traditional reactive way to a more proactive system based on intelligence gathered trough indicators that are observed trough out the phases. Normally the incident response process starts after the exploit phase putting defenders in a disadvantage position. With this method defenders should be able to move their actions and analysis up to the kill chain and interfere with the attackers actions. The authors  go even further to a more strategic level by stating that intruders reuse tools and infrastructure and they can be profiled based on the indicators. By leveraging this intelligence defenders can analyze and map multiple intrusion kill chains over time and understanding commonalties and overlapping indicators. This will result in a structural way to analyze intrusions. By repeating this process one can characterize intruders activity by determine the tactics, techniques and procedures on how the attackers operate i.e., perform a campaign analysis.

References and Further reading:

Mike Cloppert series of posts on security intelligence on the SANS Forensics Blog

Lockheed Martin Cyber Kill Chain

Sean Mason from GE on Incident Response

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Hands on Training to develop cyber security skills

abstractThe demand for qualified security professionals who possess the required skills and relevant education is increasing substantially. However, the supply is not meeting the demand. The information security industry is growing in size, density and specialization. Across all businesses we need people who understand computer systems, networks and security. In order to help facilitate the growth of these information security skills hands-on training (H.O.T.) can be used to make sure that our abilities have been tested in the most realistic way possible This paper will show how to build an environment that will represent real-world security issues and their respective flaws. Topics such as incident handling, intrusion analysis, system administration, network security, forensics or penetration testing can be taught and practiced. Among other objectives, the primary goal is to grow security expertise and awareness by using a low-cost, high return and self paced hands-on training method to allow us to understand attack methods in order to create effective defenses.

This is the abstract of my paper that was just released on the SANS reading room as part of my journey to get the GIAC GCIH gold certification. I started drafting the idea of writing a paper last October.  The experience was interesting, sometimes frustrating, long but with lots of fun. Essentially, I prepared all my ideas in the lab and practiced the different scenarios I wanted to share so they could be repeatable and consistent in order to be documented. In parallel I started to write some notes, do research and find references.  Around last December I submitted the first draft to SANS. They accepted the paper and assigned an advisor to work with me.  From that moment onwards I had a deadline of 6 months. It followed a series of back and forth with the advisor. I must admit that Dr. Johannes Ulrich from SANS was very supportive, responsive and  a great mentor during the all process.  I also would like to thank to Angel Parrizas for his constructive feedback during the paper creation and thoughts on the structure, Michael Bem for his help with the opening language, Grzegorz Drozda in the beginning with his SQL kung-fu and, finally, my family that had a lot of patience to deal with the long hours of computer.

My biggest challenge was the language in terms of structure, phrasing, diction, subject-verb agreement, and tense since English is a second language for me. I believe to create a paper like this you need strong motivation, willingness, persistence and family support but it is a rewarding experience and allowed me to share my experiences, learn, reinforce my knowledge and contribute to the community. I definitely recommend this exercise to anyone who is involved in the security industry.

The paper is available here!

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Forensics Evidence Processing – Super Timeline

After evidence acquisition, you normally start your forensics analysis and investigation by doing a timeline analysis. This is a crucial step and very useful because it includes information on when files were modified, accessed, changed and created in a human readable format, known as MAC time evidence. This activity helps finding the particular time an event took place and in which order. The traditional timeline analysis is done to the file system and has been used for several years and folks like Rob Lee and others have been championing it for years. The data is gathered using a variety of tools and is extracted from the metadata layer of the file system (inode on Linux or MFT records on Windows) and then parsed and sorted in order to be analyzed. The end goal is to generate a snapshot of the activity done in the system including its date, the artifact involved, action and source. The creation is an easy process but the interpretation is hard. During the interpretation it helps to be meticulous and patience and it facilitates if you have comprehensive file systems and operating system artifacts knowledge. To accomplish this step several commercial or open source tools exists such as the SANS Investigate Forensic Toolkit (SIFT) that is freely available and frequently updated.

In June 2010, the SANS reading room published a paper from Kristinn Gudjonsson as part of his GCFA gold certification introducing a new method called super timeline and a tool called log2timeline. The super timeline goes beyond the traditional file system timeline creation based on metadata extracted from acquired images by extending it with more sources of data in an automated fashion. As stated on Kristinn paper the super timeline includes more artifacts that provide vital information to the investigation. Basically the super timeline is a timeline of timelines that are gathered from the file system, registry keys and windows artifacts producing a single correlated timeline. To create the super timeline, Kristinn originally developed a framework that is materialized in the log2timeline tool written in Perl. The tool uses a modular approach that makes easier for someone to contribute to the project by developing a new module. A new module could be for example a new parser for a specific windows artifact. The first release  introduced several parsers for windows artifacts such as the ability to create time stamped data of Chrome, Firefox, Opera and Internet Explorer browser history, Mcafee Antivirus log file, Open XML used in the Microsoft Office documents metadata, PDF metadata, pcap network captures, UserAssist registry key and others. The log2timeline has been actively developed by Kristinn and others and its backend is currently being replaced by a new framework named Plaso that still contains the log2timeline tool as a frontend and other many other tools written in Python.

In order to practice the production of a super timeline I created a realistic scenario that consists of a Windows XP system that has been compromised by w32/Morto worm just by having remote desktop service exposed to the internet with poor administrator password. Moments after being compromised the machine was taken offline and a forensic image bit-by-bit was created.  The image was then moved to the SIFT workstation for analysis.

5 steps are needed to create the super timeline using the SIFT workstation and the front-end tool from the plaso suite.



Now with the evidence sorted and reduced I can start doing my analysis, investigation and looks for signs of Evil using for example Excel. An piece of the super timeline is showed in the following picture.



The creation of a super timeline is an easy process and it applies to different windows operating systems but the interpretation is hard.  During the interpretation it helps to be meticulous and patience and it facilitates if you have comprehensive file systems, operating system artifacts and registry knowledge. With these type of methodology one can practice and improve their ability to determine past actions which have taken place and understand all kinds of artifacts which occur within the super timeline. On the SANS website there is another great article on how to create a super timeline with log2timeline. Here you can also view a 2011 webcast that looks at what is and how to do super timeline analysis. These and other steps to create a super timeline are well detailed in the log2timeline cheat sheet created by David Nides. The analysis and investigation will be part of other post.

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Evidence acquisition – Creating a forensic image

helix-shotFollowing the identification phase of the incident handling process, where among others you have identified malicious acts or deviations from the normal operation. It comes the containment phase.  During the containment phase you want to stop the damage. Stop the bleeding and pause the attacker in the most quick and effective manner without changing evidence and using a low profile approach. There isn’t a silver bullet on how to do containment because every case is unique however there are some strategies that you can use. Some examples of short term containment include disconnecting the network cable, redirecting the impacted system DNS name to another IP address, creating a firewall rule or if your infrastructure allows put the system into a separated isolated vlan. During this process engage the business owners and decide the best approach.  Do not gracefully shutdown the system because it will destroy important evidence, artifacts and you will lose all your volatile data.

There are times that the incident handler is also gathering evidence to deliver to the forensics team or the incident handler also does the forensics analysis. Depending on the case you might be working, you might see an overlap between incident handling and forensics but the processes and procedures go hand in hand. From a forensics perspective do a forensics image of the affected system. This means gathering the file system using a disk imaging process and a memory dump (volatile data).  You should start by gathering the volatile data, then you do a disk image. With these elements you can do a thoroughly analysis of the data. During the forensics data analysis, among other things, you will look at the file system at bit level, analyzing several artifacts such as program execution, files download,  file opening and creation, usb and drive usage, account usage, browser usage, etc.

Create a forensic image of the disk as soon as is practical. Make sure you use blank media in a pristine state to create a copy of the impacted system. This blank media e.g, usb hard drive, should be wiped. You clean and prepare the drive during the preparation phase. You do not want to be wiping drives while going under fire!  To do the disk image you should do a bit-by-bit image using your preferred toolkit. Don’t use the tools from the compromised system because you cannot trust them.  Use binaries from a another source. One example is the linux based toolkit Helix that brings the dd tool built in that will assist you doing the forensic image of the hard drive – Helix product went commercial but you can still download the free 2009R3 version – .  Once you created the image and ensure its integrity, is good practice to record the time and the evidence creation method including the image hash on your incident handler notebook. If times allow create more than one image. Most of the times you don’t have time because a image creation can take several hours to execute. In such case you do a duplicate offsite and then you do your analysis using the duplicate. Image creation is a simple task but you need to practice it.

To do the image creation of the hard drives the traditional way is to remove the hard drive from the impacted system and create a forensic image using a write block. But other times this method is not practical. Another way of making a forensic image of the hard drive is to use live acquisition methods, boot disk acquisition or using remote/enterprise grade tools.  A live system acquisition might be useful in cases the affected drive is encrypted or you have a RAID across multiple drives or is not feasible to power down the machine. However, this method will only grab the logical part of the hard drive i.e. partitions such as FAT, NTFS, EXT2, etc.

The other method is using a bootable forensic distro such as Helix. You need to reboot the system and boot the system using CD/USB. This allows to create a bit-by-bit image of the physical drive, the evidence on the drive is not altered during boot process and you can create an image of the hard drive into a image file. This image file can then be used across different analysis tools and is easier to backup.

Let’s look at an hands-on scenario to create a forensic image using a bootable disk method from a compromised or suspicious system using dd. Dd is simple and flexible tool that is launched using the command line and is available for Windows and Linux. In this case we will run dd in a Linux system. What dd does is only copying chunks of raw data from one input source to an output destination. It does not know nothing about partitions or file systems. dd reads from its input source into blocks (512 bytes of data by default) specified by the if= suffix. It then writes the data to an output destination using the of= suffix.

We start by using dd to prepare a target hard drive. We will wipe the data of an hard drive that we will be using to gather the evidence. We will use dd to zeroize an 320Gb USB drive. This will render the drive sterile and into a pristine state. Plug the USB drive into a Linux system and execute fdisk -lu to display available drives on the system. In this case we have 2 drives. One is the /dev/sda which is the internal hard drive of the system and the /dev/sdb which is the 320Gb drive that we plugged into the system. The /dev/sdb does not contain any valid partitions and this is ok for now because we only want to wipe it.

root@ubuntu:~# fdisk -lu
Disk /dev/sda: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders, total 312581808 sectors
Units = sectors of 1 * 512 = 512 bytes
Disk identifier: 0x0006784f
   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048      206847      102400    7  HPFS/NTFS
Partition 1 does not end on cylinder boundary.
/dev/sda2          206848   312578047   156185600    7  HPFS/NTFS
Disk /dev/sdb: 320.0 GB, 320072933376 bytes
255 heads, 63 sectors/track, 38913 cylinders, total 625142448 sectors
Units = sectors of 1 * 512 = 512 bytes
Disk identifier: 0x00000000
Disk /dev/sdb doesn't contain a valid partition table

Next execute dd specifying as input the special file /dev/zero and the /dev/sdb as the output drive by using a block size of 8k to increase the speed of the process. This will create zeros across the entire drive. Be careful with this command and make sure you are wiping the right drive. On our system this process took more than 3 hours to complete.

root@ubuntu:~# dd if=/dev/zero of=/dev/sdb bs=8k
dd: writing `/dev/sdb': No space left on device
39071404+0 records in
39071403+0 records out
320072933376 bytes (320 GB) copied, 11579.9 s, 27.6 MB/s


The “No space left on device” error is normal. Also note that the number of records in and out multiplied by the block size (8192) will get you the number of bytes copied.

To confirm that the drive has been zeroized you can dump the contents using xxd.

root@ubuntu:~# cat /dev/sdb | xxd | more
0000000: 0000 0000 0000 0000 0000 0000 0000 0000  ................
0000010: 0000 0000 0000 0000 0000 0000 0000 0000  ................
0000020: 0000 0000 0000 0000 0000 0000 0000 0000  ................
0000030: 0000 0000 0000 0000 0000 0000 0000 0000  ................
0000040: 0000 0000 0000 0000 0000 0000 0000 0000  ................


We have now prepared our media for the acquisition process. Now that we have pristine media we can do our forensic image. Boot the Helix CD on the target/compromised system and  plug the USB media. Then create a EXT2 file system using fdisk and mke2fs.

root@ubuntu:~# fdisk /dev/sdb
Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel
Building a new DOS disklabel with disk identifier 0x7b441f7a.
Changes will remain in memory only, until you decide to write them.
After that, of course, the previous content won't be recoverable.
The number of cylinders for this disk is set to 38913.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
   (e.g., DOS FDISK, OS/2 FDISK)
Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)
Command (m for help): m
Command action
   a   toggle a bootable flag
   b   edit bsd disklabel
   c   toggle the dos compatibility flag
   d   delete a partition
   l   list known partition types
   m   print this menu
   n   add a new partition
   o   create a new empty DOS partition table
   p   print the partition table
   q   quit without saving changes
   s   create a new empty Sun disklabel
   t   change a partition's system id
   u   change display/entry units
   v   verify the partition table
   w   write table to disk and exit
   x   extra functionality (experts only) 
Command (m for help): p
Disk /dev/sdb: 320.0 GB, 320072933376 bytes
255 heads, 63 sectors/track, 38913 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x7b441f7a
   Device Boot      Start         End      Blocks   Id  System
Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4) p
Partition number (1-4): 1
First cylinder (1-38913, default 1):
Using default value 1
Last cylinder or +size or +sizeM or +sizeK (1-38913, default 38913):
Using default value 38913
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.
root@ubuntu:~# mke2fs /dev/sdb1
mke2fs 1.40.8 (13-Mar-2008)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
19537920 inodes, 78142160 blocks
3907108 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=0
2385 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks:
       32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
       4096000, 7962624, 11239424, 20480000, 23887872, 71663616
Writing inode tables: done                           
Writing superblocks and filesystem accounting information: done
This filesystem will be automatically checked every 25 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.
root@ubuntu:~# fdisk -lu
Disk /dev/sda: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders, total 312581808 sectors
Units = sectors of 1 * 512 = 512 bytes
Disk identifier: 0x0006784f
   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048      206847      102400    7  HPFS/NTFS
Partition 1 does not end on cylinder boundary.
/dev/sda2          206848   312578047   156185600    7  HPFS/NTFS
Disk /dev/sdb: 320.0 GB, 320072933376 bytes
255 heads, 63 sectors/track, 38913 cylinders, total 625142448 sectors
Units = sectors of 1 * 512 = 512 bytes
Disk identifier: 0x7b441f7a
   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1              63   625137344   312568641   83  Linux


The fdisk created a partition that used the entire disk and the mk2fs created the file system (note the command run on /dev/sdb1). Finally with the fdisk -lu you could confirm that the partition was formated using with an EXT2. The next step is mount the file system by creating a mount point and then mounting the partition.

root@ubuntu:~# mkdir /mnt/target
root@ubuntu:~# mount /dev/sdb1 /mnt/target

Then we are ready to start our bit-by-bit image creation. This method will gather the allocated space, unallocated space and slack space, bad blocks. This means will grab the all the sectors from the hard drive from the MBR to the final sector including the Host Protected Area (HPA) if it exists.

Start by creating a cryptographic fingerprint of the original disk using MD5. This will be used to verify the integrity of the duplicate. Then using dd with the input source being the /dev/sda and the output file a file named suspect.img. Other usefull options is the conv=sync,noerror to avoid stopping the image creation when founding an unreadable sector. If such sector is found with this option, it will skip over the unreadable section (noerror) and pad the output (sync). Finally create the fingerprint of the image created and verify that both fingerprints match and unmount the drive.

root@ubuntu:~# md5sum /dev/sda > /mnt/target/suspect.md5
root@ubuntu:~#dd if=/dev/sda of=/mnt/target/suspect.img conv=sync,noerror bs=8k
19536363+0 records in
19536363+0 records out
160041885696 bytes (160 GB) copied, 5669.92 s, 28.2 MB/s
root@ubuntu:~#md5sum /mnt/target/suspect.img > /mnt/target/suspect.img.md5
root@ubuntu:~# cat /mnt/target/*.md5
6a5346b9425925ed230e32c9a0b510f7  /mnt/target/suspect.img
6a5346b9425925ed230e32c9a0b510f7  /dev/sda
root@ubuntu:~# umount /mnt/target/

The creation of the image is a simple process but you should practice it. Under fire is much harder to accomplish these type of activity.  Also it is a process that can take several hours to accomplish. In our case took around 90m. The integrity checking took around the same time.  With these steps we created a forensically sound image of an hard drive in a bit-by-bit manner and we ensured its integrity.

Now that we collected a forensic image we could start our forensics investigation by doing an in-depth analysis of the file system and analyzing several artifacts such as program execution, files download,  file opening and creation, usb and drive usage, account usage, browser usage, etc.  To do this we could use the SANS Investigative Forensic Toolkit (SIFT) and start practicing tools and techniques to discover evidence and tracks about the suspect. During our investigation we might want to gather data to answer questions such as:

How did the attacker gain entry?
What is the latest evidence of attacker activity?
What actions did the attacker execute on the system?
How did the attacker maintained access to the environment?
What tools has the attacker deployed?
What accounts did the attacker compromise?



SANS Forensics 508 – Advanced Computer Forensic Analysis and Incident Response

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Computer Forensics and Investigation Methodology – 8 steps

sans-siftAccepted methods and procedures to properly seize, safeguard, analyze data and determine what happen. Actionable information to deal with computer forensic cases. Repeatable and effective steps. It’s a good way to describe the SANS methodology for IT Forensic investigations compelled by Rob Lee and many others. It is an 8 steps methodology. It will help the investigator to stay on track and assure proper presentation of computer evidence for criminal or civil case into court, legal proceedings and internal disciplinary actions, handling of malware incidents and unusual operational problems. Furthermore, is a good starting point in order to have a reasonable knowledge of forensic principles, guidelines, procedures, tools and techniques.

The purpose of these 8 steps is to respond systematically to forensic investigations and determine what happen. A similar process exists and was created by NIST on the Guide to Integrating Forensic Techniques into Incident Response  (pub. #: 800-86) published in 2006. This special publication is consistent with SANS methodology and reflect the same basic principles, differing on the granularity of each phase or terms used. Other similar methodologies are described in the ISO-27041.

Also is important to consider that a computer forensic investigation goes hand in hand with computer incident handling and is normally a break-off point of the containment phase.

Below a short and high level introduction of the 8 Computer Forensic Investigation steps:

Verification: Normally the computer forensics investigation will be done as part of an incident response scenario, as such the first step should be to verify that an incident has taken place. Determine the breadth and scope of the incident, assess the case. What is the situation, the nature of the case and its specifics. This preliminary step is important because will help determining the characteristics of the incident and defining the best approach to identify, preserve and collect evidence. It might also help justify to business owners to take a system offline.

System Description: Then it follows the step where you start gathering data about the specific incident. Starting by taking notes and describing the system you are going to analyze, where is the system being acquired, what is the system role in the organization and in the network. Outline the operating system and its general configuration such as disk format, amount of RAM and the location of the evidence.

Evidence Acquisition: Identify possible sources of data, acquire volatile and non-volatile data, verify the integrity of the data and ensure chain of custody. When in doubt of what to collect be on the safe side and is better to rather collect too much than not. During this step is also important that you prioritize your evidence collection and engage the business owners to determine the execution and business impact of chosen strategies. Because volatile data changes over time, the order in which data is collected is important. One suggested order in which volatile data should be acquired is network connections, ARP cache, login sessions, running processes, open files and the contents of RAM and other pertinent data – please note that all this data should be collected using trusted binaries and not the ones from the impacted system. After collecting this volatile data you go into the next step of collecting non-volatile data such as the hard drive. To gather data from the hard drive depending on the case there are normally three strategies to do a bit stream image: using a hardware device like a write blocker in case you can take the system offline and remove the hard drive ; using an incident response and forensic toolkit such as Helix that will be used to boot the system ; using live system acquisition (locally or remotely) that might be used when dealing with encrypted systems or systems that cannot be taken offline or only accessible remotely.  After acquiring data, ensure and verify its integrity. You should also be able to clearly describe how the evidence was found, how it was handled and everything that happened to it i.e. chain of custody.

Note that as part of your investigation and analysis the following steps work in a loop where you can jump from one into another in order to find footprints and tracks left by Evil. If you get stuck, don’t give up!

Timeline Analysis: After the evidence acquisition you will start doing your investigation and analysis in your forensics lab. Start by doing a timeline analysis. This is a crucial step and very useful because it includes information such as when files were modified, accessed, changed and created in a human readable format, known as MAC time evidence. The data is gathered using a variety of tools and is extracted from the metadata layer of the file system (inode on Linux or MFT records on Windows) and then parsed and sorted in order to be analyzed. Timelines of memory artifacts can also be very useful in reconstructing what happen. The end goal is to generate a snapshot of the activity done in the system including its date, the artifact involved, action and source. The creation is an easy process but the interpretation is hard. During the interpretation it helps to be meticulous and patience and it facilitates if you have comprehensive file systems and operating system artifacts knowledge. To accomplish this step several commercial or open source tools exists such as the SIFT Workstation that is freely available and frequently updated.

Media and Artifact Analysis: In this step that you will be overwhelmed with the amount of information that you could be looking at.  You should be able to answer questions such as what programs were executed, which files were downloaded, which files were clicked on, witch directories were opened, which files were deleted, where did the user browsed to and many others. One technique used in order to reduce the data set is to identify files known to be good and the ones that are known to be bad. This is done using databases like the Nation Software Reference Library from NIST and hash comparisons using tools like hfind from the Sleuth Kit.  In case you are analyzing a Windows system you can create a super timeline. The super timeline will incorporate multiple time sources into a single file. You must have knowledge of file systems, windows artifacts and registry artifacts to take advantage of this technique that will reduce the amount of data to be analyzed. Other things that you will be looking is evidence of account usage, browser usage, file downloads, file opening/creation, program execution, usb key usage. Memory analysis is another key analysis step in order to examine rogue processes, network connections, loaded DLLs, evidence of code injection, process paths, user handles, mutex and many others. Beware of anti-forensic techniques such as steganography or data alteration and destruction, that will impact your investigation analysis and conclusions

String or Byte search: This step will consist into using tools that will search the low level raw images. If you know what you are looking then you can use this method to find it. Is this step that you use tools and techniques that will look for byte signatures of know files known as the magic cookies. It is also in this step that you do string searches using regular expressions. The strings or byte signatures that you will be looking for are the ones that are relevant to the case you are dealing with.

Data Recovery: This is the step that you will be looking at recover data from the file system. Some of the tools that will help in this step are the ones available in the Sleuth Kit that can be used to analyze the file system, data layer and metadata layer.  Analyzing the slack space, unallocated space and in-depth file system analysis is part of this step  in order to find files of interest. Carving files from the raw images based on file headers using tools like foremost is another technique to further gather evidence.

Reporting Results: The final phase involves reporting the results of the analysis, which may include describing the actions performed, determining what other actions need to be performed, and recommending improvements to policies, guidelines, procedures, tools, and other aspects of the forensic process. Reporting the results is a key part of any investigation. Consider writing in a way that reflects the usage of scientific methods and facts that you can prove. Adapt the reporting style depending on the audience and be prepared for the report to be used as evidence for legal or administrative purposes.


References and further reading:

SANS 508 – Advanced Computer Forensics and Incident Response
Guide to Integrating Forensic Techniques into Incident Response
  (pub. #: 800-86), 2006, US NIST
Computer Security Incident Handling Guide (pub. #: 800-61), 2004, US NIST
The ComplexWorld of Corporate CyberForensics Investigations by Gregory Leibolt


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