This is article was originally posted by Unit 42 author, Tomar Bar
This post is the first in a new series titled "Examining the Cybercrime Underground". Each post will delve into different aspects of how cybercriminals operate, using current examples of tools and techniques. What are their tools of the trade? How do they get them? How do they overcome challenges posed by security and anti-fraud systems? How do criminals profit from scams and turn stolen data into cash? Answering these questions will help readers better understand one of their primary cyberadversaries and use that knowledge to better protect their networks.
What is a Crypter?
Crypters are software tools that use a combination of encryption, obfuscation, and code manipulation of malware to make them FUD (Fully Undetectable) by legacy security products.
Why Do Attackers Use Crypters?
To understand the role that crypters play in cybercrime, it’s helpful to try to understand the cybercriminal mindset. The Holy Grail for cybercriminals is fully undetectable malware that would allow them to use the same malware repeatedly without being detected by a security solution. They also want their attacks randomized to make sure that the failure of one attack won’t affect the outcome of attacks against other victims. Knowing this, let’s look at a common attack scenario used by cybercriminals. Cybercriminals often use Remote Administration Tools (RAT) to steal online banking credentials, credit card numbers, personal data, or other valuable pieces of information. One of the oldest and and most widely used RAT is DarkComet. This tool lets criminals perform a variety of functions including:
Steal passwords and credit card numbers
Download, upload, delete, and rename files
Install viruses and worms
Edit a computer’s registry
Silently install applications
Log keystrokes or install keystroke capture software
Open a CD-ROM tray
Control the mouse or keyboard
Record sound with a connected microphone
Record video with a connected webcam
Shutdown, restart, or log-off the computer
Record and control a victim’s screen remotely
View, kill, and start tasks in task manager
This screen shot, for example, shows an attacker eavesdropping on a webcam session using a RAT on the attacker’s CNC server:
But using DarkComet is a problem for the attacker’s perspective, because almost any legacy security solution can detect it.
For example, this DarkComet sample has 47/56 detection rate from VirusTotal.com
However, using crypters will allow the cybercriminal to bypass legacy security solutions and use the DarkComet tool undetected.
How does a newbie cybercriminal find himself a crypter? It’s surprisingly easy. A Google search for “fud crypter download” yielded 152,000 results, including places where crypter software can be purchased just as easily as a legitimate software download.
Palo Alto Networks researchers recently detected a new cybercrime campaign using the notorious DataScrambler crypter, previously disclosed and analyzed in the Unit 42 research paper 419 Evolution.
Data Scrambler Updates
It seems that since the publication of our the crypter developer/seller rebranded the crypter “LightCore” as “DataScrambler.”
LightCore crypter GUI on the left compared to DataScrambler GUI on the right.
LightCore feature list is identical to the DataScrambler’s feature list mentioned in the 419 Evolution paper. Even the order in which the features are listed order remained the same:
This is the promotions website page content:
“Welcome to DataScrambler!”
DataScrambler is the most advanced crypter on the market and has tons of features for a cheap price. You cannot go wrong with our product and on top of the cheap prices, you get free support and updates.
Full Support for "Customers"
The “semi-commercial” seller offers full support services, and the following is one attacker’s instructions for his “customers”
“I want to make it clear to all customers, in case the crypted file should become detected, it will be updated within 48 hours. Please do not post your issues or detections in the sales thread. For help with DataScrambler, click on the help button, Please read the guide before contacting me.”
Terms of Service Comparison
Original Crypter Developer/Seller Identity
As it seems that the original DataScrambler developer/seller has changed, there are two different scenarios:
The original developer is using a new identity, or
The original developer sold the crypter code/copyrights to another developer/seller
Based on publicly available data, the original identity behind DataScrambler is:
This person mentioned that in the past he worked for Cheetah Mobile (the number two Internet and mobile security company in China which is not related to this crypter in any way). But we can assume the developer’s security knowledge and experience was to develop this crypter.
Case Study: The Saga Continues
A recent attack using advanced crypter starts by spear phishing with RAR attachment:
In another attack, the attacker sent the spear phishing mail under a stolen identity, “GPS Trading” company founder and CEO, Mr. Panos Dimitriadis. The attachment name is Quotation_inquiry.scr (also sent to import[at]gpstrading.com).
Please note that GPSTrading Company is not connected to this attack and the attacker used their CEO’s identity in an effort to exploit the victim’s trust and to increase the infection’s probability of success.
We have discovered the following new attacks, publicly unknown so far, using those sha256 hashes:
The CNC Server address won’t be published here because it’s still active. It is a Windows based server with FTP, cifs and Windows terminal server interfaces.
The file attached to the email “ New Purchase Order.rar” contains: first stage SFX infector – sample.exe
sha256 – 02c80443fb49915b1943b44ab8ec4dce5b1ca53f3fcdb84fae23abcf45d34a66 unknown to VirusTotal.com
sample.exe is SFX (self-executable) with a fake pdf icon that contains one executable file and many others with random extensions:
The SFX contains a lot of junk commands (for bypassing legacy security solutions) but in the in the middle it hides the command to auto-execute dmpbr.exe with parameter dhwdv.gko. This is one of the files in the SFX.
It’s a benign file although on Virus Total it scores 2/56 (2 false positive from VirusTotal.com).
Cypter's First Stage - DHWDV.GKO
AutoIt script – this is the crypter’s first stage.
sha256 – f8dc0013a94017cc19b8f865948daf83b64692db47199a994efab032d8b737f3 unknown to VirusTotal.
The file contains a lot of junk data to bypass legacy security solutions by using obfuscated commands (like raw 435)
The script reads data from the other scripts (extracted from the SFX file) which in turn read data from another script and so on. In the end, a final obfuscated crypter script is built.
We successfully de-obfuscated the final script. For example, all strings internal AutoIt functions and Windows API functions used by the crypter are obfuscated with a simple but working algorithm (reverse hex bytes and decode them to ASCII strings).
This is a simple python tool we scripted to DE-obfuscate the strings:
Final Crypter File
sha256- 082b41f71cc5a5118e1f70f49e059763d48fc072e7fc28f8efb11076537461f3 is 3/52 from VirusTotal (but it is textual so can be changed without much effort by the attacker).
This crypter supports:
Decrypt DarkComet with RC2 decryption algorithm in memory, check the registry for the default browser, creates browser process suspended, write DarkComet to verified signed browser process, uses setThreadContext to change the execution flow to the injected code and resume the process and delete itself.
The result is signed browser executable (in our case it is Chrome and signed by Google
1c9e1a3aef25e34ea0fda67d3840c53a5449d63db6e9070f6dfc66f2fef92b15 0/55) that connects to DarkComet CNC execute attackers command.
No unsigned file is written to disk beside the AutoIt obfuscated textual files and signed trusted AutoIt.
The crypter adds its own capabilities (beside DarkComet) by reading the commands from YMQGIX, an INI file:
Facebook password stealing
Disable task manager (not working on the analyzed sample, because of attackers misspellings, (check wrong process name instead of taskmgr.exe)
Disable system restore
We suspect we found a bug in the anti-emulator code. It works by opening mshta.exe seven times and killing it and then loops until those processes are killed, but it is unclear why the author assumes that will protect him from emulators.
See crypter’s code of anti-emulator function:
Anti-VM, Download and Execute of Another Malware
INI Config File - YMQGIX
INI commands and settings for crypter
sha256 – c547ad05ebed04bad9e5509cb979413fb05c88bfab6313ef110a00b035de9aad is unknown to VirusTotal.
RC2 Encrypted Malware Extap
rc2 encrypted malware decrypted by the crypter on runtime
sha256-7f88d9a894da7b2ccfb331d223307cc0c94730849f4b58a8fa43513ba98c4b63 unknown to VirusTotal.
The cybercrime underground is evolving, and enterprises using legacy security solutions won’t be protected without a next-generation enterprise security platform. Our next post on the cybercrime underground will be focused on the after-attack phases, including how attackers use victims’ credit card data to steal money, and the current state of the phishing market underground.