Pierluigi Paganini December 19, 2013

Kaspersky Lab experts have discovered a new Tor-based banking trojan named “ChewBacca”, it is the last malware exploiting Tor network.

Tor network is a territory of exploration for cybercriminals that are increasing their attention in the popular anonymizing network for make more resilient malicious botnets. The principal advantages for adoption of hidden service in a botnet architecture are:

• Availability of Authenticated Hidden Services.
• Availability Private Tor Networks
• Possibility of Exit Node Flooding

Exploiting Tor based botnet cybercriminals can hide their control infrastructures making hard theit eradication to law enforcement and security firms. In the last months security experts have found different malware variants abusing Tor network to create bulletproof botnets including Skynet, Mevade  and Atrax. Also last version of Zeus malware designed for 64 bit architectures has implemented the possibility to use Tor to avoid detection of its C&C servers.

Security Researchers at Kaspersky Lab have recently discovered a new Tor-based malware, dubbed “ChewBacca” (“Trojan.Win32.Fsysna.fej”), used by cybercriminals to hit banking users stealing their credentials. The C&C server login page has an image of a character ChewBacca from the film series Star Wars that’s the origin of the name for the botnet.

As observed for last variant of Zeus also the C&C of this trojan is hosted on a Tor .onion domain. to preserve server from being tracked. But Tor is still too slow, and massive botnets may have an impact on the performances of the overall network as observed for the Mevade botnet, in this case the botnet is very noisy and easy to destroy.

The Kaspersky Lab team hasn’t provided information on the extension of the Chewbacca botnet neither the circumstances that led the experts to discover it, consider that Chewbacca is currently not publicly available on the underground market.

Chewbacca code was compiled with Free Pascal 2.7.1., once executed windows based system, it drops as spoolsv.exe in the startup folder and also drops a copy of Tor 0.2.3.25.

“After execution, the function “P$CHEWBACCA$_$TMYAPPLICATION_$__$$_INSTALL” is called, which drops itself as “spoolsv.exe” into the “Startup folder” (e.g. C:\Documents and Settings\All Users\Start Menu\Programs\Startup\) and requests the public IP of the victim via a publicly accessible service at http://ekiga.net/ip (which is not related to the malware). Tor is dropped as “tor.exe” to the user-s Temp and runs with a default listing on “localhost:9050″.”

The Chewbacca Trojan logs all keystrokes by the user to “system.log” under the user’s local Temp folder and then sends the data back to the botnet controllers via Tor anonymity network. Chewbacca also enumerates all running processes and reads their process memory, another characteristic is that the C&C server is a LAMP platform (Linux, Apache, MySQL and PHP).

Tor isn’t the unique anonymizing network used by cyber criminals, Russian hackers have recently proposed i2Ninja financial malware based on the I2P network for the same reason.

In the future we will see more example of such malware improved to work with different anonymizing networks, multiplatform and multi protocol.

Pierluigi Paganini

(Security Affairs –  Tor-based malware, ChewBacca)