TrickBot operators continue to update their malware to increase resilience to takedown

Following the recent takedown, the TrickBot operators have implemented various improvements to make it more resilient.

In October, Microsoft’s Defender team, FS-ISAC, ESET, Lumen’s Black Lotus Labs, NTT, and Broadcom’s cyber-security division Symantec joined the forces and announced a coordinated effort to take down the command and control infrastructure of the infamous TrickBot botnet.

Even if Microsoft and its partners have brought down the TrickBot infrastructure TrickBot operators attempted to resume the operations by setting up new command and control (C&C) servers online.

Following the takedown, the operators behind the TrickBot malware have implemented several improvements to make it more resilient.

A few days after the TrickBot takedown, Netscout researchers spotted a new TrickBot Linux variant that was used by its operators.

Security researchers also reported that the TrickBot botnet was used to spread other threats, such as Ryuk ransomware.

Now Bitdefender researchers reported that the Trickbot authors have provided multiple updates to increase the resilience of the botnet and improve its reconnaissance capabilities.

“The group behind TrickBot seems to have actively pushed new versions of the Trojan and maintained the full list of modules used in previous versions. However, in the recently analyzed samples, it seems that the shareDll – or mshareDll in its packed version – was no longer present. In fact, now there’s only the shareDll, which is packed, with mshareDll completely removed.” reads the analysis published by BitDefender. “This probably indicates that TrickBot operators are moving away from unpacked modules, cleaning up their list of lateral movement modules to only use packed ones.”

The operators are not using only packed modules in the new versions and some version update responses are digitally signed with bcrypt to prevent takedown.

The version number of the sample spotted by BitDefender in early November is 2000016 (the latest version before the takedown was 1000513),

The analysis of the C2 infrastructure revealed that botnet operators are using Mikrotik routers as command and control servers and implement a backup mechanism for the C2 through an EmerDNS domain.

What’s more, the malware operators appear to have switched to using MikroTik routers as C&C servers, and were observed using an EmerDNS domain as a backup server. According to Bitdefender, the same EmerCoin key used to administer the server is also employed in the administration of C&C servers for the Bazar backdoor.

“What’s interesting about this particular domain is that the EmerCoin key (EeZbyqoTUrr4TpnBk67iApX2Wj3uFbACbr) used to administer the server, also administers some C&C servers that belong to the Bazar backdoor.” contunues the analysis. “The analyzed sample (82e2de0b3b9910fd7f8f88c5c39ef352) uses the morganfreeman.bazar domain, which has the 81.91.234.196 IP address and running Mikrotik v6.40.4.”

Experts also observed important differences between the lists of plugin server configurations, TrickBot operators have apparently eliminated the Tor plugin services and have added the new <psrva> tags, likely obfuscated IPs. This technique was also implemented by the Bazar backdoor.

The new version of the malware appears to have been involved mainly in attacks aimed at systems in Malaysia, the United States, Romania, Russia, and Malta.

According to the popular malware researcher Vitili Kramez, the new TrickBot version also includes a new reconnaissance module called LightBot, which allows attackers to identify systems of interest within the target’s network.

“Completely dismantling TrickBot has proven more than difficult, and similar operations in the past against popular Trojans has proven that the cybercriminal community will always push to bring back into operation something that’s profitable, versatile and popular.” concludes Bitdefender. “TrickBot might have suffered a serious blow, but its operators seem to be scrambling to bring it back, potentially more resilient and difficult to extirpate than ever before.”

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Pierluigi Paganini

(SecurityAffairs – hacking, malware)

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