Anatomy of Ryuk Attack: 29 Hours From Initial Email to Full Compromise

An attack involving the Ryuk ransomware required 29 hours from an email being sent to the target to full environment compromise and the encryption of systems, according to the DFIR Report, a project that provides threat intelligence from real attacks observed by its honeypots.

Initially detailed in 2018, Ryuk was believed to be the work of North Korean hackers at first, due to similarities with the Hermes ransomware, but was then associated with Russian cybercriminals.

Over the past two years, Ryuk has been responsible for a significant number of high-profile attacks, including incidents involving Pennsylvania-based UHS and Alabama hospital chain DCH Health System.

In the case of the attack observed by the DFIR Report, it all started with a malicious email that carried a link to download the Bazar/Kegtap loader, which injects into multiple processes, and which performs reconnaissance on the infected system, using Windows utilities like nltest and net group, as well as third-party tool AdFind.

The malware remained quiet for roughly one day, after which a second reconnaissance phase was launched, using the same tools, plus Rubeus. Data was exfiltrated to a remote server and the attackers started lateral movement.

To compromise additional systems on the network, the attackers used various methods, including remote WMI, remote service execution with PowerShell, and a Cobalt Strike beacon dropped over SMB. Next, the Cobalt Strike beacon was used as the main pivotal point.

Additional beacons were then established across the environment and PowerShell was employed to disable Windows Defender. Ryuk was executed one minute after being transferred over SMB from the pivot and, once encryption started, the servers used to store backups were hit first.

The DFIR Report, which provides a comprehensive technical analysis of the attack, reveals that Ryuk was also transferred to the remaining hosts on the network via SMB, and that an RDP connection was leveraged to execute it from the pivot domain controller.

“In total, the campaign lasted 29 hours–from initial execution of the Bazar, to domain wide ransomware. If a defender missed the first day of recon, they would have had a little over 3 hours to respond before being ransomed,” The DFIR Report notes.

After the systems were encrypted, the attackers demanded approximately 600 Bitcoins (roughly $6 million) in ransom. However, the threat actors were willing to negotiate.

On Monday, Microsoft announced that it shut down the infrastructure of TrickBot, the botnet used as the main delivery channel for Ryuk ransomware.

Related: Hacked Hospital Chain Says All 250 US Facilities Affected

Related: Human-Operated Ransomware Is a Growing Threat to Businesses: Microsoft

Related: Ryuk Ransomware Damages Large Files Following Update

Related: Pitney Bowes Says Disruptions Caused by Ryuk Ransomware

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Ionut Arghire is an international correspondent for SecurityWeek.

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