SOPs in DFIR by David Cowen - Hacking Exposed Computer Forensics Blog

Hello Reader,
      It's been awhile! Sorry I haven't written sooner. Things are great here at camp aka G-C Partners where the nerds run the show. 2 years ago or so I got lucky enough to work with on our favorite customers in generating some standard operating procedures for their DFIR lab. While we list forensic lab consulting as a service on our website we don't get to engage in helping other labs improve as often as I'd like.

It may sound like a bad idea for a consulting company to help a potential client get better at what we both do, some may see this as a way of preventing future work for yourself. This in my view is short sighted and in my world view of DFIR and especially in the court testimony/expert witness world the better the internal lab is the better my life is when they decide to litigate a case. If I've helped you get on the same standard of work as my lab then I can spend my time using the prior work as a cheat sheet to validate faster and then looking for the newest techniques or research that could potentially find additional evidence.

Now beyond the business aspects of helping another lab improve I want to talk about the general first reactions that I get and used to have myself regarding making SOPs for what we do. SOP or Standard Operating Procedures are a good thing (TM) as they help set basic standards in methodology, quality and templated output without the expense of creative solutions... if they are done right.

When I was still doing penetration testing work I was first asked to try and make SOPs for my job. I balked at the idea stating that you can't proceduralize my work, there are too many variables! While this was true for the entire workflow what I didn't want to admit at the time is that there we were several parts of my normal work that were ripe for procedures to be created. I didn't want to admit it because that would mean additional work for myself in creating documentation I saw as something that would slow down my job. When I started doing forensic work in 1999 I was asked the same question for my DFIR work and again pushed back stating there were too many variables in an investigation to try to turn it into a playbook.

I was wrong then and you may be wrong now. The first thing you have to admit to yourself, and your coworkers, is that regardless of the outliers in our work there are certain things we always do. Creating these SOPs will let new and existing team members do more consistent work and create less work for yourself in continually repeating yourself on what to do and what they should give you at the end of it. This kind of SOP will work for you if you create a SOP that works more like a framework than a restrictive set of steps.

For examples of how SWGDE makes SOPs for DFIR look here:

Read on to see what I do.

What you want:

  • You want the SOP for a particular task to work more like stored knowledge 
  • You want to explain what that particular task can and can't do to prevent confusion or misinformation
  • You want to establish what to check for to make sure everything ran correctly to catch errors early and often
  • You want to provide alternative tools or techniques that work in case your preferred tool or method fails
  • You want to link to tool documentation or blogs/articles that give more documentation on whats being done in case people want to know more
  • You want to establish a minimum set of requirements for what the output is to prevent work being done twice
  • You want to store these somewhere accessible and easy to access like a wiki/sharepoint/dropbox/google doc so people can easily refer to them and more importantly you can easily refer people to it
  • You want to build internal training that works to teach people how to perform tasks with the SOPs so they become part of your day to day work not 'that thing' that no one wants to use
  • You want your team to be part of making the SOP more helpful while keeping to these guidelines of simplicity and usability

What you don't want:

  • You don't want to create a step by step process for someone to follow, that's not a SOP those are instructions
  • You don't want to create a checklist of things to do, if you do that people will only follow the checklist and feel confined to it
  • You don't to use words like must/shall/always unless you really mean it, whatever you write in your SOP will be used to judge your work. Keep the language flexible and open so they serve as a guideline that you as an expert can navigate around when needed
  • You don't want to put a specific persons name or email address in, people move around and your SOPs will quickly fall out of date
  • You don't want to update your SOPs every time a tool version changes, so make sure you are not making them so specific that change of one choice or parameter breaks them
  • You don't want to make these by committee, just assign them to people with an example SOP you've already made and then show them to team for approval/changes

In the end what you are aiming for is to have a series of building blocks of different common tasks you have in your investigative procedures that you can chain together for different kinds of cases.

If that's hard to visualize lets go through an example SOP for prefetch files and how it fits into a larger case flow. In this example I am going to show the type of data I would put into the framework, not the the actual SOP I would write. 

Why not just give you my SOP for prefetch files? My SOP will be different from yours. We have an internal tool for preftech parsing, I want different output to feed our internal correlation system and I likely want more data than most people think is normal. 

Example framework for Prefetch files:

Requirements per SOP:

  •     Scope
    •  This SOP covers parsing Prefetch files on Windows XP-8.1. 
  • Limitations
    • The prefetch subsystem may be disabled if the system you are examining is running an SSD and is Windows 7 or newer or if running a server version of Windows. The prefetch directory only stores prefetch files for the last 128 executables executed on Windows XP - 7. You will need to recover shadow copies of preftech files and carve for prefetch files to find all possible prefetch entries on an image.
  •  Procedure
    • Extract prefetch files
    • Parse prefetch files with our preferred tool,
  •   Expected output
    • A json file for each prefetch
  •   Template for reporting
    • Excel spreadsheet, see prefetch.xlsx for an example 
  •  QA steps
    • Validate that timestamps are being correctly formatted in excel
    • If there are no prefetch files determine if a SSD was present or if anti forensics occurred
  •  Troubleshooting
    • Make sure timestamps look correct
    • Validate that paths and executable names fit within columns
    • Make sure the number of prefetch files present equal to the number of files you parsed
    • Remember for windows 10 that the prefetch format changed, you must use the Win10 Prefetch SOP
    • Remember that Windows Server OS's do not have Prefetch on my default
  • Alternative tools 
    • Tzworks pf 
  • Next Steps
    • Shimcache parsing
  • References
    • Links to prefetch format from metz 

Now you have a building block SOP for just parsing PE files. Now you can create workflows that combine a series of SOPs that guides an examiner without locking them into a series of steps. Here is an example for a malware case. 

Malware workflow:
  1. Identify source of alert and indicators to look for
  2. Follow triage SOP
  3. Volatility processes SOP
  4. Prefetch SOP
  5. Shimcache SOP
  6. MFT SOP
  7. Userassist SOP
  8. timeline SOP
  9. Review prior reports to find likely malicious executable
You can then reuse the same SOPs for other workflows that range from intrusions to intellectual property cases. The goal is not to document how to do an entire case but to standardize and improve the parts you do over and over again for every case with an eye on automating and eliminating errors to make you job easier/better and your teams work better. 

Now I don't normally do this but if you are looking at this and saying to yourself, I don't have the time or resources to do this but I do have the budget for help then reach out: or me specifically

We do some really cool stuff and we can help you do cool stuff as well. I try to keep my blogs technical and factual but I feel that sometimes I hold back on talking about what we do to the detriment of you the reader. So to be specific for customers who do engage us to help them improve their labs/teams we :

1. Provide customized internal training on SOPs, Triforce, internal tools, advanced topics
2. Create custom tools for use in your environment to automate correlation and workflows
3. Create SOPs and processes around your work
4. Provide Triforce and internal G-C tool site licenses and support
5. Do internal table top scenarios 
6. Do report and case validation to check on how your team is performing and what you could do better
7. Build out GRR servers and work with your team to teach you how to use it and look for funny business aka threat hunting
8. Act as a third party to evaluate vendors trying to sell you DFIR solutions

Ok there I'm done talking about what we do, hopefully this helps someone. I'll be posting again soon about my new forensic workstation and hopefully more posts in the near future.

Post a Comment