Ryuk is a ransomware designed to target enterprise environments that has been used in attacks since at least 2018. Ryuk shares code similarities with Hermes ransomware.[1][2][3]

ID: S0446
Platforms: Windows
Contributors: The DFIR Report, @TheDFIRReport; Matt Brenton, Zurich Insurance Group
Version: 1.2
Created: 13 May 2020
Last Modified: 18 August 2021

Techniques Used

Domain ID Name Use
Enterprise T1134 Access Token Manipulation

Ryuk has attempted to adjust its token privileges to have the SeDebugPrivilege.[1]

Enterprise T1547 .001 Boot or Logon Autostart Execution: Registry Run Keys / Startup Folder

Ryuk has used the Windows command line to create a Registry entry under HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run to establish persistence.[1]

Enterprise T1059 .003 Command and Scripting Interpreter: Windows Command Shell

Ryuk has used cmd.exe to create a Registry entry to establish persistence.[1]

Enterprise T1486 Data Encrypted for Impact

Ryuk has used a combination of symmetric (AES) and asymmetric (RSA) encryption to encrypt files. Files have been encrypted with their own AES key and given a file extension of .RYK. Encrypted directories have had a ransom note of RyukReadMe.txt written to the directory.[1][4]

Enterprise T1083 File and Directory Discovery

Ryuk has called GetLogicalDrives to emumerate all mounted drives, and GetDriveTypeW to determine the drive type.[1]

Enterprise T1222 .001 File and Directory Permissions Modification: Windows File and Directory Permissions Modification

Ryuk can launch icacls /grant Everyone:F /T /C /Q to delete every access-based restrictions on files and directories.[5]

Enterprise T1562 .001 Impair Defenses: Disable or Modify Tools

Ryuk has stopped services related to anti-virus.[2]

Enterprise T1490 Inhibit System Recovery

Ryuk has used vssadmin Delete Shadows /all /quiet to to delete volume shadow copies and vssadmin resize shadowstorage to force deletion of shadow copies created by third-party applications.[1]

Enterprise T1036 Masquerading

Ryuk can create .dll files that actually contain a Rich Text File format document.[5]

.005 Match Legitimate Name or Location

Ryuk has constructed legitimate appearing installation folder paths by calling GetWindowsDirectoryW and then inserting a null byte at the fourth character of the path. For Windows Vista or higher, the path would appear as C:\Users\Public.[1]

Enterprise T1106 Native API

Ryuk has used multiple native APIs including ShellExecuteW to run executables,GetWindowsDirectoryW to create folders, and VirtualAlloc, WriteProcessMemory, and CreateRemoteThread for process injection.[1]

Enterprise T1027 Obfuscated Files or Information

Ryuk can use anti-disassembly and code transformation obfuscation techniques.[4]

Enterprise T1057 Process Discovery

Ryuk has called CreateToolhelp32Snapshot to enumerate all running processes.[1]

Enterprise T1055 Process Injection

Ryuk has injected itself into remote processes to encrypt files using a combination of VirtualAlloc, WriteProcessMemory, and CreateRemoteThread.[1]

Enterprise T1021 .002 Remote Services: SMB/Windows Admin Shares

Ryuk has used the C$ network share for lateral movement.[6]

Enterprise T1053 .005 Scheduled Task/Job: Scheduled Task

Ryuk can remotely create a scheduled task to execute itself on a system.[5]

Enterprise T1489 Service Stop

Ryuk has called kill.bat for stopping services, disabling services and killing processes.[1]

Enterprise T1614 .001 System Location Discovery: System Language Discovery

Ryuk has been observed to query the registry key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Nls\Language and the value InstallLanguage. If the machine has the value 0x419 (Russian), 0x422 (Ukrainian), or 0x423 (Belarusian), it stops execution.[1]

Enterprise T1016 System Network Configuration Discovery

Ryuk has called GetIpNetTable in attempt to identify all mounted drives and hosts that have Address Resolution Protocol (ARP) entries.[1][6]

Enterprise T1205 Traffic Signaling

Ryuk has used Wake-on-Lan to power on turned off systems for lateral movement.[6]

Enterprise T1078 .002 Valid Accounts: Domain Accounts

Ryuk can use stolen domain admin accounts to move laterally within a victim domain.[5]

Groups That Use This Software

ID Name References
G0102 Wizard Spider


G0037 FIN6