Pierre Cadieux, Colin Grady, Jaeson Schultz and Matt Valites said in a blog post that Sodinokibi attempted to encrypt data in a user's home directory and delete the shadow copy backups to make recovery that bit more difficult.

They said Oracle has issued a patch for this issue, outside its normal patch cycle, on 26 April. "This vulnerability is easy for attackers to exploit, as anyone with HTTP access to the WebLogic server could carry out an attack. Because of this, the bug has a CVSS score of 9.8/10," they wrote.

"Attackers have been making use of this exploit in the wild since at least 17 April."

The initial release of the ransomware was on 25 April, a day before the Oracle patch arrived, with the researchers reasoning that this a trial to see if the server could be exploited. The next day, the attackers made an HTTP connection to a second vulnerable server, requesting the AsyncResponderService of the Oracle WebLogic Server.

"Historically, most varieties of ransomware have required some form of user interaction, such as a user opening an attachment to an email message, clicking on a malicious link, or running a piece of malware on the device," Cadieux, Grady, Schultz and Valites wrote.

One variant of the ransom note generated by Sodinokibi.

"In this case, the attackers simply leveraged the Oracle WebLogic vulnerability, causing the affected server to download a copy of the ransomware from attacker-controlled IP addresses 188.166.74[.]218 and 45.55.211[.]79. The 188.166.74[.]218 IP address is also home to a pair of other malicious domains unrelated to this ransomware attack: arg0s-co[.]uk, which is likely a phishing domain, and projectstore[.]guru, a domain with bogus PDF-related Google search results.

"The other IP, 45.55.211[.]79, hosts a pair of legitimate Chilean domains, and appears to have been infected and repurposed by the attackers. The attackers were ultimately successful at encrypting a number of systems during this incident."

A second variant of the ransom note.

They found that about eight hours after the initial attack, the same group attempted to exploit the same vulnerability with a different ransomware variant, Gandcrab.

"We find it strange the attackers would choose to distribute additional, different ransomware on the same target," the researchers wrote. "Sodinokibi being a new flavour of ransomware, perhaps the attackers felt their earlier attempts had been unsuccessful and were still looking to cash in by distributing Gandcrab."

They said given the fact that Oracle WebLogic servers were present in large numbers, more attacks were expected in coming days.

Screenshots: Courtesy Cisco Talos Intellligence Group