Note: Description is based on analysis of sample (SHA1) 524e1011c26b6bf7e23f5d107222397129f9893d.
In addition to stealing login details, Trojan.Agent.Formbook can also:
- Capture screenshots,
- Delete user cookies,
- Try to connect to google.com to confirm Internet connectivity,
- Contact a remote site (its C&C server) to download and install other files,
- Forward any stolen data to the C&C server,
- Disable the Task Manager,
- And shut down and restart the computer.
The trojan is spread as a specially-crafted document file attached to spam email messages. If the user opens the attached file, the trojan is launched.
Trojan.Agent.Formbook checks the computer for any common anti-debugging techniques or keywords, such as "VM", "Sandbox", “"VMWare Users.exe", and "VMWare Service". If any are found, the trojan immediately exits.
This step is intended to make it harder for security researchers to analyze the malware.
The trojan adds the following registry key to the Windows registry so that it will automatically run whenever the computer is started:
Trojan.Agent.Formbook drops multiple script files with random extensions in a folder named CNE in the Temp folder, with most being decoys to camouflage its actual usable components. Examples of some of the files it drops are:
The trojan uses the following command to run the pwm-axa script file:
- C:\Users\user\AppData\Local\Temp\cne\axo.exe pwm-axa
It then runs another script file, this one with a random name. As an example, the script file CDWDY is run next using the following argument:
- C:\Users\user\AppData\Local\Temp\cne\axo.exe CDWDY
This script launches a new thread and injects it into the explorer.exe process by using the following sequence of command prompts:
- "/c copy "%TEMP%\RegSvcs.exe"
- "%PROGRAMFILES%\colorcpl79b.bat" /V
- "/c del "%TEMP%\RegSvcs.exe
From there, the trojan can begin monitoring the Firefox browser for activity.
If the user opens Facebook's login page in the Firefox browser, Trojan.Agent.Formbook steals any data the user enters into the login form on the page. The stolen data is then forwarded to the trojan's C&C server.
The trojan attempts to connect to the following remote servers: