Posté par: igor51 le avril 25, 2019, 12:00:21
One,
Two and
Three of CARBANAK Week are behind us. In this final blog post, we
dive into one of the more interesting tools that is part of the
CARBANAK toolset. The CARBANAK authors wrote their own video player
and we happened to come across an interesting video capture from
CARBANAK of a network operator preparing for an offensive engagement.
Can we replay it?
About the Video Player
The CARBANAK backdoor is capable of recording video of the victim’s
desktop. Attackers reportedly
recorded desktop videos to gain an understanding of the
operational workflow of employees working at targeted banks, allowing
them to successfully insert fraudulent transactions that remained
undetected by the banks’ verification processes. As mentioned in a
previous blog post
the arrest of several FIN7 members, the video data file format
and the player used to view the videos appeared to be custom written.
The video player, shown in Figure 1, and the C2 server for the bots
were designed to work together as a pair.
Figure 1: CARBANAK desktop video player
The C2 server wraps video stream data received from a CARBANAK bot
in a custom video file format that the video player understands, and
writes these video files to a location on disk based on a convention
assumed by the video player. The StreamVideo
constructor shown in Figure 2 creates a new video file that will be
populated with the video capture data received from a CARBANAK bot,
prepending a header that includes the signature
infected host. This code is part of the C2 server project.
Figure 2:
carbanak\server\Server\Stream.cs – Code snippet from the C2 server
that serializes video data to file
Figure 3 shows the LoadVideo function that
is part of the video player project. It validates the file type by
looking for the TAG signature, then reads
the timestamp values and IP address just as they were written by the
C2 server code in Figure 2.
Figure 3:
carbanak\server\Player\Video.cs – Player code that loads a video
file created by the C2 server
Video files have the extension .frm as
shown in Figure 4 and Figure 5. The C2 server’s
formats a file path following a convention defined in the
StreamVideo constructor from Figure 2.
Figure 4:
carbanak\server\Server\RecordFromBot.cs – Function in the C2 server
that formats a video file name and adds the extension "frm"
The video player code snippet shown in Figure 5 follows video file
path convention, searching all video file directories for files with
the extension .frm that have begin and end
timestamps that fall within the range of the
Figure 5:
carbanak\server\Player\Video.cs – Snippet from Player code that
searches for video files with "frm" extension
An Interesting Video
We came across several video files, but only some were compatible
with this video player. After some analysis, it was discovered that
there are at least two different versions of the video file format,
one with compressed video data and the other is raw. After some slight
adjustments to the video processing code, both formats are now
supported and we can play all videos.
Figure 6 shows an image from one of these videos in which the person
being watched appears to be testing post-exploitation commands and
ensuring they remain undetected by certain security monitoring tools.
Figure 6: Screenshot of video playback
captured by CARBANAK video capability
The list of commands in the figure centers around persistence,
screenshot creation, and launching various payloads. Red teamers often
maintain such generic notes and command snippets for accomplishing
various tasks like persisting, escalating, laterally moving, etc. An
extreme example of this is Ben Clark’s book
In advance of an operation, it is customary to tailor the file names,
registry value names, directories, and other parameters to afford
better cover and prevent blue teams from drawing inferences based on
methodology. Furthermore, Windows behavior sometimes yields surprises,
such as value length limitations, unexpected interactions between
payloads and specific persistence mechanisms, and so on. It is in the
interest of the attacker to perform a dry run and ensure that
unanticipated issues do not jeopardize the access that was gained.
The person being monitored via CARBANAK in this video appears to be
a network operator preparing for attack. This could either be because
the operator was testing CARBANAK, or because they were being
monitored. The CARBANAK builder and other interfaces are never shown,
and the operator is seen preparing several publicly available tools
and tactics. While purely speculation, it is possible that this was an
employee of the front company Combi Security which we
know was operated by FIN7 to recruit potentially unwitting
operators. Furthermore, it could be the case that FIN7 used CARBANAK’s
tinymet command to spawn Meterpreter
instances and give unwitting operators access to targets using
publicly available tools under the false premise of a penetration test.
Conclusion
This final installment concludes our four-part series, lovingly
dubbed CARBANAK Week. To recap, we have shared at length many details
concerning our experience as reverse engineers who, after spending
dozens of hours reverse engineering a large, complex family of
malware, happened upon the source code and toolset for the malware.
This is something that rarely ever happens!
We hope this week’s lengthy addendum to FireEye’s continued CARBANAK
research has been interesting and helpful to the broader security
community in examining the functionalities of the framework and some
of the design considerations that went into its development.
So far we have received lots of positive feedback about our
discovery of the source code and our recent exposé of the CARBANAK
ecosystem. It is worth highlighting that much of what we discussed in
CARBANAK Week was originally covered in our FireEye’s Cyber Defense
Summit 2018 presentation titled “
Carbanak!”, which is
available to watch online (a must-see for malware and lederhosen
enthusiasts alike). You can expect similar topics and an electrifying
array of other malware analysis, incident response, forensic
investigation and threat intelligence discussions at FireEye’s
upcoming Cyber Defense
Summit 2019, held Oct. 7 to Oct. 10, 2019, in Washington, D.C.
Source: CARBANAK Week Part Four: The CARBANAK Desktop Video Player (http://)