Posté par: igor51 le juillet 26, 2019, 21:00:17
Rekall Tools
Paging all digital forensicators, incident responders, and memory
manager enthusiasts! Have you ever found yourself at a client site
working around the clock to extract evil from a Windows 10 image? Have
you hit the wall at step zero, running into difficulties
viewing a process tree, or enumerating kernel modules? Or even worse,
had to face the C-Suite and let them know you couldn’t find any evil?
Well fear no more – FLARE has you covered. We've analyzed Windows 10
and integrated our research into
Volatility and
Rekall tools for your immediate consumption!
Until August 2013, as a skilled consultant, you were generally in
good shape. Your tools worked as you expected them to and you were
able to forensicate rapidly. Windows 8.1 introduced changes that began
to break the tools we know and love. This breakdown largely went
unnoticed as most companies continued using Windows 7, but now
corporate environments are rolling out Windows 10 images at an
ever-increasing pace and forensic tools haven’t kept up.
This blog post is the first in a three-part series covering our
Windows 10 memory forensics research. This post coincides with Omar
Sardar and Blaine Stancill’s presentation at
DFIR Austin 2019 and is designed to introduce you to FLARE’s
updates to
Rekall. The
next post will coincide with our
USA 2019 presentation, in which Omar Sardar and Dimiter Andonov
will dig into the nitty-gritty details of the Windows 10 memory
manager. The final post will serve as a guide to those seeking to
analyze the kernel on their own.
Overview
Traditionally, a complete Windows memory analysis only required
forensic tools to parse physical memory and fill in any missing gaps
from the pagefile. In Windows 8.1 Microsoft upended this paradigm with
the introduction of memory compression and a new virtual store
designed to contain compressed memory. While current tools can inspect
traditional pagefiles on disk just fine, the virtual store poses a
challenge due to sparse documentation and data compression.
To enable a more complete memory analysis on Windows 10, FireEye’s
FLARE team analyzed the operating system’s memory manager as well as
the algorithms and structures used to retrieve compressed memory. The
memory we’re looking for is stored in a virtual store, created by the
Store Manager kernel component. The Store Manager is responsible for
managing data involved in performance optimization systems, including
SuperFetch, ReadyBoost, and ReadyDrive. In this case, the Virtual
Store is a RAM-backed entity, leveraging storage space in
MemCompression.exe for processes’
compressed data. The results of this research have been ported to both
Volatility and Rekall to benefit the security community.
Volatility and Rekall
Volatility
and Rekall are
two of the most popular open-source memory forensic frameworks
available. With the introduction of Windows memory compression, both
frameworks have been unable to read compressed pages – until now! The
effects of compression were immediately noticeable as many plugins
previously reported missing data or did not work altogether. To
demonstrate, we will utilize a common plugin called
modules that lists drivers loaded at
the time of memory capture. In Figure 1, drivers loaded on the system
are enumerated, but several paths to the files on disk are paged out
to the compression store. These missing paths could very well be the
evil you were hunting!
Figure 1: Volatility & Rekall missing
data stored in compressed pages
To deal with missing data due to compressed pages, FireEye's FLARE
team made multiple additions to
Rekall to
support Windows 10 memory compression. First and foremost, we added
the necessary overlays:
An overlay describes the internal data structures used by the
Windows 10 memory compression algorithm and makes them available in
Python. For example, the overlays define the layout of the
SMKM_STORE structure and the
B+Trees used to lookup compressed
pages. These structures, among others, will be described in additional
detail in Part Two of this blog series.
The undocumented Windows structures defined in the overlays are
based on information we obtained through analyzing different versions
of Windows 10. Being undocumented, these structures are susceptible to
change across Windows builds, and even revisions. We currently support
versions 1607, 1703, 1709, 1803, and 1809 on both 32-bit and 64-bit
architectures. To support additional versions, the layout of the
structures must be analyzed and the overlays updated accordingly.
Analyzing the kernel to extract these structures will be discussed
further in both Part Two and Part Three of this blog series.
The second modification to support compressed pages includes new
address spaces for each framework:
- WindowsIA32CompressedPagedMemoryPae
- WindowsAMD64CompressedPagedMemory
- Win10CompressedIA32PagedMemoryPae
- Win10CompressedIA32PagedMemory
- Win10CompressedAMD64PagedMemory
Address spaces are responsible for satisfying memory read requests.
When stacked on top of one another, each layer can translate the read
request to an underlying base layer abstracting away the details of
how the actual read is performed. An example translation is converting
a virtual address to a physical address. Depending on the bottommost
layer, the physical address may be an offset into a memory image,
crash dump, or hibernate file. The takeaway is that an address space
transparently resolves memory, regardless of its location and – most
importantly – with zero effort on your part. Due to this seamless
integration, users can interact with Volatility and Rekall just as
before and, if a compressed page is detected, the new address spaces
will take care of decompression in the background and return the
decompressed data.
Back to our previous
modules plugin example, Figure 2
demonstrates how the newly implemented address spaces properly
decompress data located in compressed pages. No more hidden drivers or
DLLs, among a plethora of other forensic artifacts. The data is now
yours to continue your hunt for evil!
Figure 2: Volatility & Rekall
decompressing compressed data
Get It Today
Head over to our
Rekall GitHub
repositories to start using them today. After downloading or cloning
the repositories, follow any necessary installation instructions as
outlined on each GitHub's
README page and start finding that evil!
Conclusion
Windows 10 memory compression is a significant evolution in the
design of the memory manager that increases system performance by
making a more efficient use of physical memory. This increase in
performance comes at the cost of a more complex memory management
system that is currently not publicly documented. Up until now,
Volatility and Rekall were unable to inspect memory stored in
compressed pages, opening the door to malicious programs and forensics
artifacts going undetected. FireEye’s FLARE team hopes to fill the
knowledge and technical gaps for Windows 10 compressed memory through
contributions to Volatility and Rekall, as well as in presentations
given at
DIFR (Finding Evil in Windows 10 Compressed Memory) and
USA 2019. We look forward to seeing you there and hearing your
feedback, and we’re excited to see how these frameworks develop as a
result of our contributions! Stay tuned for Part Two of our Finding
Evil in Windows 10 Compressed Memory blog series.
Source: Finding Evil in Windows 10 Compressed Memory, Part One: Volatility and
Rekall Tools (http://)