New variants of the Zeusbot/SpyEye cybercrime toolkit are moving away from reliance on command-and-control (C&C) servers towards a peer-to-peer architecture.
C&C servers are the Achilles heel of cybercrime networks, vulnerable to both takedown operations and monitoring by either law enforcement or police. Variants of Zeusbot/SpyEye released last year got around the takedown-leads-to-decapitation problem by building in peer-to-peer functionality that allowed compromised hosts to exchange information on replacement C&C servers.
Now cybercrooks have built functionality into Zeusbot/SpyEye that allows instructions to be distributed via P2P techniques as well, eliminating the need for C&C servers. Compromised systems are now capable of downloading commands, configuration files, and executables from other bots, a write-up by security researchers at Symantec explains.
"Previously, every compromised computer was a peer in the botnet and the configuration file (containing the URL of the C&C server) was distributed from one peer to another," Symantec researcher Andrea Lelli explains. "This way, even if the C&C server was taken down, the botnet was still able to contact other peers to receive configuration files with URLs of new C&C servers."
"With the latest update, it seems that the C&C server has disappeared entirely for this functionality. Where they were previously sending and receiving control messages to and from the C&C, these control messages are now handled by the P2P network."
Stolen data (banking login credentials) and the like can be transmitted over the P2P network, instead of dumped on servers that might be infiltrated. However preliminary analysis suggest that stolen data is still transmitted back to attackers directly rather than relayed through the P2P network.
Nonetheless tracking banking botnet activity and identifying the cybercrooks behind such networks is likely to become more difficult as a result of the architectural changes that have come with the latest version of ZeuS/SpyEye, Symantec warns. Other changes to the malware creation toolkit include greater reliance on UDP communications – a stateless protocol that's harder to track and dump than TCP – as well as an extra encryption layer.
Both ZeuS and SpyEye are best described as cybercrime toolkits that can be used for the creation of customised banking Trojans. The code base of the two former rivals was merged last year, leading to the creation of strains designed to target mobile banking customers.
The source code of ZeuS was leaked last May, further propelling innovation in the underground cybereconomy. Previously licences to ZeuS – sold via carder forums and other underground forums – could fetch thousands of dollars a pop. But since the source code leak, any tech-savvy cybercrook can knit their own banking Trojan. ®