FireEye is tracking a set of financially-motivated activity referred to as TEMP.MixMaster that involves the interactive deployment of Ryuk ransomware following TrickBot malware infections. These operations have been active since at least December 2017, with a notable uptick in the latter half of 2018, and have proven to be highly successful at soliciting large ransom payments from victim organizations. In multiple incidents, rather than relying solely on built-in TrickBot capabilities, TEMP.MixMaster used EMPIRE and RDP connections to enable lateral movement within victim environments. Interactive deployment of ransomware, such as this, allows an attacker to perform valuable reconnaissance within the victim network and identify critical systems to maximize their disruption to business operations, ultimately increasing the likelihood an organization will pay the demanded ransom. These operations have reportedly netted about $3.7 million in current BTC value.
Notably, while there have been numerous reports attributing Ryuk malware to North Korea, FireEye has not found evidence of this during our investigations. This narrative appears to be driven by code similarities between Ryuk and Hermes, a ransomware that has been used by APT38. However, these code similarities are insufficient to conclude North Korea is behind Ryuk attacks, as the Hermes ransomware kit was also advertised for sale in the underground community at one time.
It is important to note that TEMP.MixMaster is solely a reference to incidents where we have seen Ryuk deployed following TrickBot infections and that not all TrickBot infections will lead to the deployment of Ryuk ransomware. The TrickBot administrator group, which is suspected to be based in Eastern Europe, most likely provide the malware to a limited number of cyber criminal actors to use in operations. This is partially evident through its use of “gtags” that appear to be unique campaign identifiers used to identify specific TrickBot users. In recent incidents investigated by our Mandiant incident response teams, there has been consistency across the gtags appearing in the configuration files of TrickBot samples collected from different victim networks where Ryuk was also deployed. The uniformity of the gtags observed across these incidents appears to be due to instances of TrickBot being propagated via the malware’s worming module configured to use these gtag values.