Security researchers have discovered a new variant of the Ryuk ransomware that is targeting web servers.
According to a blog post by Marc Elias, a security researcher on the McAfee Advanced Threat Research team, Ryuk ransomware has shifted its attention to web servers since it no longer encrypts the index file but replaces it with the ransom note instead.
Elias said that the Ryuk infection chain usually starts with a spear phishing email that includes a malicious URL or Office document to gain initial entry into victim environments.In certain cases, compromised RDP computers provide the initial access.
In the first scenario, either Trickbot or BazarLoader will be executed and used as a loader malware, offering other actors the opportunity to purchase hacked machines.
Once access to the victim’s machines is acquired by the ransomware actors, a Cobalt Strike beacon is often downloaded in order to obtain users’ credentials and move laterally on the network to take over the domain controllers. Finally, the Ryuk binary is distributed to every machine from the domain controllers.
Elias said that Ryuk copies itself three times in the current directory with different names and launches these new executables with distinct command lines to execute different functionality in each execution.To notify the user about the encryption, Ryuk drops an HTML ransom note in every folder that it encrypts.
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“This note is remarkably similar to the note used in other Ryuk variants, with the only difference being the use of a contact button with some instructions to install the Tor Browser,” said Elias.
After file encryption, the ransomware will print 50 copies of the ransom note on the default printer.
Elias said that organizations should be on the lookout for traces and behaviors that correlate to open source pen test tools such as winPEAS, Lazagne, Bloodhound and Sharp Hound, or hacking frameworks like Cobalt Strike, Metasploit, Empire or Covenant, as well as abnormal behavior of non-malicious tools that have a dual use.
“These seemingly legitimate tools (e.g., ADfind, PSExec, PowerShell, etc.) can be used for things like enumeration and execution. Subsequently, be on the lookout for abnormal usage of Windows Management Instrumentation WMIC (T1047),” he said.
Elias added that in the first half of the year, several Ryuk actors have been known to be actively launching new campaigns and targeting organizations all over the world.
“This is the reason we believe the criminals behind Ryuk will continue to develop new features and invent new methods to maximize their profits,” he added.
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