Cybercriminals increasingly use the Tor network to control their botnets, researchers say

Researchers from ESET discovered two new malware threats that use control servers within the Tor anonymity network

Malware writers are increasingly considering the Tor anonymity network as an option for hiding the real location of their command-and-control (C&C) servers, according to researchers from security firm ESET.

The ESET researchers recently came across two botnet-type malware programs that use (C&C) servers operating as Tor "hidden services."

The Tor Hidden Service protocol allows users to set up services -- usually Web servers -- that can only be accessed from within the Tor network through a random-looking hostname that ends in the .onion pseudo domain extension.

This protocol was designed to hide the real Internet Protocol (IP) address of a "hidden service" from its clients as well as hide the clients' IP addresses from the service, making it almost impossible for either party to determine the other's location or identity.

The traffic between a Tor client and a Tor hidden service is encrypted and is randomly routed through a series of computers participating in the network and acting as relays.

Using Tor to host botnet command-and-control (C&C) servers is not a new idea. The strengths and weaknesses of such an approach were discussed in a presentation at the DefCon 18 security conference in 2010.

Practical implementations of this concept have also been seen in the past. In December, researchers from security firm Rapid7 identified the Skynet botnet of 12,000 to 15,000 compromised computers that were receiving commands from an Internet Relay Chat (IRC) server running as a Tor hidden service. The researchers warned at the time that other malware writers were likely to adopt the design.

Two new malware programs discovered by ESET recently suggest that their prediction was right.

"In July ESET researchers detected two different types of TOR-based botnets based on the malware families Win32/Atrax and Win32/Agent.PTA," ESET malware researchers Anton Cherepanov and Aleksandr Matrosov said Wednesday in a blog post. "Both botnets have form-grabbing functionality for possible further fraud operations."

Unlike Skynet, the Atrax and Agent.PTA botnets use Web, not IRC, servers hidden on the Tor network for command and control purposes.

Atrax can download, execute and inject malicious files into browser processes. Its functionality can be extended through plug-ins that are encrypted locally with an AES key generated from the hardware parameters of each infected computer.

Atrax comes with a Tor client component that gets injected into the local browser in order to route the malware's C&C traffic over the Tor network.

The ESET researchers were able to trick the Atrax C&C server into sending two additional plug-ins to a test system infected with the malware. One of them was designed to steal information entered into Web forms and the other was capable of stealing passwords.

The other threat identified in July, called Agent.PTA, is part of a malware family known since 2012, the ESET researchers said. However, the Tor functionality is a new addition to it, they said.

Like Atrax, Agent.PTA has form-grabbing capabilities and its functionality can also be extended through plug-ins. The malware connects to Web control servers operated as Tor hidden services.

"This year we had already detected TOR-based botnets but during the summer we have observed a growth in the numbers of malware families starting to use TOR-based communications," the ESET researchers said. "The TOR-based botnets make it really hard to pursue investigation and C&C location tracking."

However, even if locating the real IP addresses of the C&C servers is difficult when they are only accessible from within the Tor network, analyzing the malware's communication protocols and command and control traffic is still doable, the researchers said.

Join the newsletter!

Or

Sign up to gain exclusive access to email subscriptions, event invitations, competitions, giveaways, and much more.

Membership is free, and your security and privacy remain protected. View our privacy policy before signing up.

Error: Please check your email address.

Tags privacymalwareonline safetyesetRapid7

Keep up with the latest tech news, reviews and previews by subscribing to the Good Gear Guide newsletter.

Lucian Constantin

IDG News Service
Show Comments

Cool Tech

Toys for Boys

Family Friendly

Stocking Stuffer

SmartLens - Clip on Phone Camera Lens Set of 3

Learn more >

Christmas Gift Guide

Click for more ›

Brand Post

Most Popular Reviews

Latest Articles

Resources

PCW Evaluation Team

Aysha Strobbe

Microsoft Office 365/HP Spectre x360

Microsoft Office continues to make a student’s life that little bit easier by offering reliable, easy to use, time-saving functionality, while continuing to develop new features that further enhance what is already a formidable collection of applications

Michael Hargreaves

Microsoft Office 365/Dell XPS 15 2-in-1

I’d recommend a Dell XPS 15 2-in-1 and the new Windows 10 to anyone who needs to get serious work done (before you kick back on your couch with your favourite Netflix show.)

Maryellen Rose George

Brother PT-P750W

It’s useful for office tasks as well as pragmatic labelling of equipment and storage – just don’t get too excited and label everything in sight!

Cathy Giles

Brother MFC-L8900CDW

The Brother MFC-L8900CDW is an absolute stand out. I struggle to fault it.

Luke Hill

MSI GT75 TITAN

I need power and lots of it. As a Front End Web developer anything less just won’t cut it which is why the MSI GT75 is an outstanding laptop for me. It’s a sleek and futuristic looking, high quality, beast that has a touch of sci-fi flare about it.

Emily Tyson

MSI GE63 Raider

If you’re looking to invest in your next work horse laptop for work or home use, you can’t go wrong with the MSI GE63.

Featured Content

Don’t have an account? Sign up here

Don't have an account? Sign up now

Forgot password?