Vawtrak malware uses steganography to hide update files in favicons

Pierluigi Paganini March 26, 2015

A new strain of Vawtrak malware implements capabilities to send and receive data through encrypted favicons distributed over the Tor network.

A new powerful variant of the Vawtrak malware, also known as Neverquest or Snifula, appeared in the wild.

Vawtrak is considered by malware researchers one of the most dangerous malicious code that is threatening systems worldwide.

The researcher, Jakub Kroustek from AVG anti-virus firm, has published a detailed analysis of the new strain of Vawtrak. The expert has detailed the new features implemented by the authors of the malware.

Vawtrak is a financial malware, among the new features implemented by criminals there is the capability to send and receive data through encrypted favicons spread over the anonymizing Tor network.
Vawtrak uses steganography to hide the update file in the favicons, each favicon is approximately 4 kB.
Vawtrak implements injections mechanisms and API Hooking in order to steal financial information, FTP credentials, private keys and execute banking transactions from victim’s PC hiding its activities. The variant of Vawtrak detected by AVG is able to run man-in-the-middle attacks and grab videos and screenshots from the compromised host.

According to the experts, Vawtrak infects victims via malware downloaders (e.g. Zemot, Chaintor), exploit kits, or through drive-by downloads (e.g. spam email attachments or malicious links).

According to data collected by AVG in Q1 2015, The infections of the Vawtrak malware are most prevalent in the Czech Republic, USA, UK, and Germany.


The popular malware implements several methods to steal victim’s passwords, including the use of the Pony password stealing module.

“As we mentioned in the introduction, Vawtrak supports several methods for stealing a user’s passwords. The first method is based on monitoring the data sent by a web browser. The second method is provided by the Pony password stealing module.” states the report.

According to Kroustek, Vawtrak uses Tor2Web proxy to receive updates from its developers.

“Of particular interest from a security standpoint is that by using Tor2web proxy, it can access update servers that are hosted on the Tor hidden web services without installing specialist software such as Torbrowser,” said the expert. “Moreover, the communication with the remote server is done over SSL, which adds further encryption.”

Once executed on the victim’s machine, Vawtrak performs the following actions:

  • Disables antivirus protection. Communicates with remote C&C servers – executes commands
  • Communicates with remote C&C servers – executes commands from a remote server, sends stolen information, downloads new versions of itself and web-injection frameworks.Hooks standard API functions, injects itself into new processes.
  • Steals passwords, digital certificates, browser history, and cookies.
  • Logs keystrokes.
  • Takes screenshots of  desktop or particular windows with highlighted mouse clicks.
  • Hooks standard API functions, injects itself into new processes.
  • Steals passwords, digital certificates, browser history, and cookies. 
  • Captures user actions on desktop in an AVI video.
  • Opens a VNC11 (Virtual Network Computing) channel for a remote control of the infected machine.
  • Creates a SOCKS12 proxy server for communication through the victim’s computer.
  • Changes or deletes browser settings (e.g. disable Firefox SPDY13) and history. Vawtrak supports three major browsers to operate in – Internet Explorer, Firefox, and Chrome. It also supports password stealing from the other browsers.
  • Modifies browser communication with a web server.
  • Stores internal settings into encrypted registry keys.

Stay Tuned for more information and enjoy the report from AVG!

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Pierluigi Paganini

(Security Affairs –  AVG,   Vawtrak)

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