This advisory uses the MITRE Adversarial Tactics, Techniques, and Common Knowledge (ATT&CK®) version 7 framework. See the ATT&CK for Enterprise version 7 for all referenced threat actor tactics and techniques.
This joint cybersecurity advisory was coauthored by the Cybersecurity and Infrastructure Security Agency (CISA), the Federal Bureau of Investigation (FBI), and the Department of Health and Human Services (HHS). This advisory describes the tactics, techniques, and procedures (TTPs) used by cybercriminals against targets in the Healthcare and Public Health Sector (HPH) to infect systems with Ryuk ransomware for financial gain.
CISA, FBI, and HHS have credible information of an increased and imminent cybercrime threat to U.S. hospitals and healthcare providers. CISA, FBI, and HHS are sharing this information to provide warning to healthcare providers to ensure that they take timely and reasonable precautions to protect their networks from these threats.
Click here for a PDF version of this report.
Since 2016, the cybercriminal enterprise behind Trickbot malware has continued to develop new functionality and tools increasing the ease, speed, and profitability of victimization. What began as a banking trojan and descendant of Dyre malware, now provides its operators a full suite of tools to conduct a myriad of illegal cyber activities. These activities include credential harvesting, mail exfiltration, cryptomining, point-of-sale data exfiltration, and the deployment of ransomware, such as Ryuk. In early 2019, the FBI began to observe new Trickbot modules named Anchor, which cyber actors typically used in attacks targeting high-profile victims—such as large corporations. These attacks often involved data exfiltration from networks and point-of-sale devices. As part of the new Anchor toolset, Trickbot developers created Anchor_DNS, a tool for sending and receiving data from victim machines using Domain Name System (DNS) tunneling.
Anchor_DNS is a backdoor that allows victim machines to communicate with command and control (C2) servers over DNS to evade typical network defense products and make their malicious communications blend in with legitimate DNS traffic. Anchor_DNS uses a single-byte XOR cipher to encrypt its communications, which have been observed using key 0xB9. Once decrypted, the string Anchor_DNS can be found in the DNS request traffic.
After successful execution of the malware, Trickbot copies itself as an executable file with a 12-character (includes .exe), randomly generated file name (e.g. mfjdieks.exe) and places this file in one of the following directories.
The malware may also drop a file named anchorDiag.txt in one of the directories listed above.
Prior to initiating communications with the C2 server, the malware uses an infection marker of Global\fde345tyhoVGYHUJKIOuy, typically found in the running memory of the victim machine.
Part of the initial network communications with the C2 server involves sending information about the victim machine such as its computer name/hostname, operating system version, and build via a base64-encoded GUID. The GUID is composed of /GroupID/ClientID/ with the following naming convention:
/anchor_dns/[COMPUTERNAME]_[WindowsVersionBuildNo].[32CharacterString]/.
The malware uses scheduled tasks that run every 15 minutes to ensure persistence on the victim machine. The scheduled task typically uses the following naming convention.
[random_folder_name_in_%APPDATA%_excluding_Microsoft]
autoupdate#[5_random_numbers] (e.g., Task autoupdate#16876).
After successful execution, Anchor_DNS further deploys malicious batch scripts (.bat) using PowerShell commands.
The malware deploys self-deletion techniques by executing the following commands.
The following domains found in outbound DNS records are associated with Anchor_DNS.
This malware used the following legitimate domains to test internet connectivity.
The Anchor_DNS malware historically used the following C2 servers.
Typically Ryuk has been deployed as a payload from banking Trojans such as Trickbot. (See the United Kingdom (UK) National Cyber Security Centre (NCSC) advisory, Ryuk Ransomware Targeting Organisations Globally, on their ongoing investigation into global Ryuk ransomware campaigns and associated Emotet and TrickBot malware.) Ryuk first appeared in August 2018 as a derivative of Hermes 2.1 ransomware, which first emerged in late 2017 and was available for sale on the open market as of August 2018. Ryuk still retains some aspects of the Hermes code. For example, all of the files encrypted by Ryuk contain the HERMES tag but, in some infections, the files have .ryuk added to the filename, while others do not. In other parts of the ransomware code, Ryuk has removed or replaced features of Hermes, such as the restriction against targeting specific Eurasia-based systems.
While negotiating the victim network, Ryuk actors will commonly use commercial off-the-shelf products—such as Cobalt Strike and PowerShell Empire—in order to steal credentials. Both frameworks are very robust and are highly effective dual-purpose tools, allowing actors to dump clear text passwords or hash values from memory with the use of Mimikatz. This allows the actors to inject malicious dynamic-link library into memory with read, write, and execute permissions. In order to maintain persistence in the victim environment, Ryuk actors have been known to use scheduled tasks and service creation.
Ryuk actors will quickly map the network in order to enumerate the environment to understand the scope of the infection. In order to limit suspicious activity and possible detection, the actors choose to live off the land and, if possible, use native tools—such as net view, net computers, and ping—to locate mapped network shares, domain controllers, and active directory. In order to move laterally throughout the network, the group relies on native tools, such as PowerShell, Windows Management Instrumentation (WMI), Windows Remote Management , and Remote Desktop Protocol (RDP). The group also uses third-party tools, such as Bloodhound.
Once dropped, Ryuk uses AES-256 to encrypt files and an RSA public key to encrypt the AES key. The Ryuk dropper drops a .bat file that attempts to delete all backup files and Volume Shadow Copies (automatic backup snapshots made by Windows), preventing the victim from recovering encrypted files without the decryption program.
In addition, the attackers will attempt to shut down or uninstall security applications on the victim systems that might prevent the ransomware from executing. Normally this is done via a script, but if that fails, the attackers are capable of manually removing the applications that could stop the attack. The RyukReadMe file placed on the system after encryption provides either one or two email addresses, using the end-to-end encrypted email provider Protonmail, through which the victim can contact the attacker(s). While earlier versions provide a ransom amount in the initial notifications, Ryuk users are now designating a ransom amount only after the victim makes contact.
The victim is told how much to pay to a specified Bitcoin wallet for the decryptor and is provided a sample decryption of two files.
Initial testing indicates that the RyukReadMe file does not need to be present for the decryption script to run successfully but other reporting advises some files will not decrypt properly without it. Even if run correctly, there is no guarantee the decryptor will be effective. This is further complicated because the RyukReadMe file is deleted when the script is finished. This may affect the decryption script unless it is saved and stored in a different location before running.
According to MITRE, Ryuk uses the ATT&CK techniques listed in table 1.
Table 1: Ryuk ATT&CK techniques
| Technique | Use |
|---|---|
| System Network Configuration Discovery [T1016] | Ryuk has called GetIpNetTable in attempt to identify all mounted drives and hosts that have Address Resolution Protocol entries. |
|
Masquerading: Match Legitimate Name or Location [T1036.005] |
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. |
| Process Injection [T1055] | Ryuk has injected itself into remote processes to encrypt files using a combination of VirtualAlloc, WriteProcessMemory, and CreateRemoteThread. |
| Process Discovery [T1057] | Ryuk has called CreateToolhelp32Snapshot to enumerate all running processes. |
| Command and Scripting Interpreter: Windows Command Shell [T1059.003] | Ryuk has used cmd.exe to create a Registry entry to establish persistence. |
| File and Directory Discovery [T1083] | Ryuk has called GetLogicalDrives to enumerate all mounted drives, and GetDriveTypeW to determine the drive type. |
| Native API [T1106] | Ryuk has used multiple native APIs including ShellExecuteW to run executables, GetWindowsDirectoryW to create folders, and VirtualAlloc, WriteProcessMemory, and CreateRemoteThread for process injection. |
| Access Token Manipulation [T1134] | Ryuk has attempted to adjust its token privileges to have the SeDebugPrivilege. |
| Data Encrypted for Impact [T1486] | Ryuk has used a combination of symmetric and asymmetric 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. |
| Service Stop [T1489] | Ryuk has called kill.bat for stopping services, disabling services and killing processes. |
| Inhibit System Recovery [T1490] | Ryuk has used vssadmin Delete Shadows /all /quiet to delete volume shadow copies and vssadmin resize shadowstorage to force deletion of shadow copies created by third-party applications. |
| Boot or Logon Autostart Execution: Registry Run Keys / Startup Folder [T1047.001] | Ryuk has used the Windows command line to create a Registry entry under HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run to establish persistence. |
| Impair Defenses: Disable or Modify Tools [T1562.001] | Ryuk has stopped services related to anti-virus. |
For a downloadable copy of IOCs, see AA20-302A.stix.
CISA, FBI, and HHS encourage HPH Sector organizations to maintain business continuity plans—the practice of executing essential functions through emergencies (e.g., cyberattacks)—to minimize service interruptions. Without planning, provision, and implementation of continuity principles, organizations may be unable to continue operations. Evaluating continuity and capability will help identify continuity gaps. Through identifying and addressing these gaps, organizations can establish a viable continuity program that will help keep them functioning during cyberattacks or other emergencies. CISA, FBI, and HHS suggest HPH Sector organizations review or establish patching plans, security policies, user agreements, and business continuity plans to ensure they address current threats posed by malicious cyber actors.
CISA, FBI and HHS do not recommend paying ransoms. Payment does not guarantee files will be recovered. It may also embolden adversaries to target additional organizations, encourage other criminal actors to engage in the distribution of ransomware, and/or fund illicit activities. In addition to implementing the above network best practices, the FBI, CISA and HHS also recommend the following:
System administrators who have indicators of a Trickbot network compromise should immediately take steps to back up and secure sensitive or proprietary data. Trickbot infections may be indicators of an imminent ransomware attack; system administrators should take steps to secure network devices accordingly. Upon evidence of a Trickbot infection, review DNS logs and use the XOR key of 0xB9 to decode XOR encoded DNS requests to reveal the presence of Anchor_DNS, and maintain and provide relevant logs.
This section is based on CISA and Multi-State Information Sharing and Analysis Center (MS-ISAC)'s Joint Ransomware Guide, which can be found at https://ift.tt/2F5M7yR.
CISA, FBI, and HHS recommend that healthcare organizations implement both ransomware prevention and ransomware response meaures immediately.
CISA, FBI, and HHS recommend that healthcare organizations take the following initial steps:
Join a healthcare information sharing organization, H-ISAC:
Engage with CISA and FBI, as well as HHS—through the HHS Health Sector Cybersecurity Coordination Center (HC3)—to build a lasting partnership and collaborate on information sharing, best practices, assessments, and exercises.
Engaging with the H-ISAC, ISAO, CISA, FBI, and HHS/HC3 will enable your organization to receive critical information and access to services to better manage the risk posed by ransomware and other cyber threats.
Refer to the best practices and references below to help manage the risk posed by ransomware and support your organization’s coordinated and efficient response to a ransomware incident. Apply these practices to the greatest extent possible based on availability of organizational resources.
Remember: Paying the ransom will not ensure your data is decrypted or that your systems or data will no longer be compromised. CISA, FBI, and HHS do not recommend paying ransom.
Should your organization be a victim of ransomware, CISA strongly recommends responding by using the Ransomware Response Checklist located in CISA and MS-ISAC's Joint Ransomware Guide, which contains steps for detection and analysis as well as containment and eradication.
Upon voluntary request, CISA can assist with analysis (e.g., phishing emails, storage media, logs, malware) at no cost to support your organization in understanding the root cause of an incident, even in the event additional remote assistance is not requested.
CISA, FBI, and HHS recommend identifying and having on hand the following contact information for ready use should your organization become a victim of a ransomware incident. Consider contacting these organizations for mitigation and response assistance or for purpose of notification.
To report suspicious or criminal activity related to information found in this Joint Cybersecurity Advisory, contact your local FBI field office at www.fbi.gov/contact-us/field, or the FBI’s 24/7 Cyber Watch (CyWatch) at (855) 292-3937 or by email at CyWatch@fbi.gov. When available, please include the following information regarding the incident: date, time, and location of the incident; type of activity; number of people affected; type of equipment used for the activity; the name of the submitting company or organization; and a designated point of contact. To request incident response resources or technical assistance related to these threats, contact CISA at Central@cisa.dhs.gov.
Additionally, see the CISA and MS-ISAC's Joint Ransomware Guide for information on contacting—and what to expect from contacting—federal asset response contacts and federal threat response contacts.
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