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Introduction

1.         Every Cybersecurity Security Agency (CSA) is aware that the all businesses having sensitive data & Critical Infrastructures (CI) are targets for the ransomware attack. Hence businesses and Critical Infrastructures (CI) asset owners and operators to adopt a heightened state of awareness and implement the recommendations listed in the Mitigations section, including implementing robust network segmentation between IT and Operation Technology networks; regularly testing manual controls; and ensuring that backups are implemented, regularly tested, and isolated from network connections. These mitigations will help CI owners and operators improve their entity’s functional resilience by reducing their vulnerability to ransomware and the risk of severe business degradation if impacted by ransomware.

Mitigations

2.         CI owners and operators to apply the following mitigations to reduce the risk of compromise by ransomware attacks.

• Require multi-factor authentication for remote access to Operation Technology and IT networks.

• Enable strong spam filters to prevent phishing emails from reaching end users. Filter emails containing executable files from reaching end users.

• Implement a user training program and simulated attacks for spearphishing to discourage users from visiting malicious websites or opening malicious attachments and re-enforce the appropriate user responses to spearphishing emails.

• Filter network traffic to prohibit ingress and egress communications with known malicious IP addresses. Prevent users from accessing malicious websites by implementing URL blocklists and/or allow lists.

• Update software, including operating systems, applications, and firmware on IT network assets, in a timely manner. Consider using a centralized patch management system; use a risk-based assessment strategy to determine which Operation Technology network assets and zones should participate in the patch management program.

• Limit access to resources over networks, especially by restricting RDP. After assessing risks, if RDP is deemed operationally necessary, restrict the originating sources and require multi-factor authentication.

• Set antivirus/antimalware programs to conduct regular scans of IT network assets using up-to-date signatures. Use a risk-based asset inventory strategy to determine how Operation Technology  network assets are identified and evaluated for the presence of malware.

• Implement unauthorized execution prevention by:

• Disabling macro scripts from Microsoft Office files transmitted via email. Consider using Office Viewer software to open Microsoft Office files transmitted via email instead of full Microsoft Office suite applications.

• Implementing application allowlisting, which only allows systems to execute programs known and permitted by security policy. Implement Software Restriction Policies (SRPs) or other controls to prevent programs from executing from common ransomware locations, such as temporary folders supporting popular internet browsers or compression/decompression programs, including the    AppData/ LocalAppData folder.

• Monitor and/or block inbound connections from Tor exit nodes and other anonymisation services to IP addresses and ports for which external connections are not expected (i.e., other than VPN gateways, mail ports, web ports).

• Deploy signatures to detect and/or block inbound connection from Cobalt Strike servers and other post exploitation tools.

3.         CI owners and operators to apply the following mitigations now to reduce the risk of severe business or functional degradation should their CI entity fall victim to a ransomware attack in the future.

• Implement and ensure robust network segmentation between IT and Operation Technology  networks to limit the ability of adversaries to pivot to the Operation Technology  network even if the IT network is compromised. Define a DMZ (Demilitarized Zone) that eliminates unregulated communication between the IT and Operation Technology  networks.

• Organize Operation Technology  assets into logical zones by taking into account criticality, consequence, and operational necessity. Define acceptable communication conduits between the zones and deploy security controls to filter network traffic and monitor communications between zones. Prohibit Industrial Control System (ICS) protocols from traversing the IT network.

• Identify Operation Technology  and IT network inter-dependencies and develop workarounds or manual controls to ensure ICS networks can be isolated if the connections create risk to the safe and reliable operation of Operation Technology  processes. Regularly test contingency plans such as manual controls so that safety critical functions can be maintained during a cyber incident. Ensure that the Operation Technology  network can operate at necessary capacity even if the IT network is compromised.

• Regularly test manual controls so that critical functions can be kept running if ICS or Operation Technology  networks need to be taken offline.

• Implement regular data backup procedures on both the IT and Operation Technology  networks. Backup procedures should be conducted on a frequent, regular basis. The data backup procedures should also address the following best practices:

• Ensure that backups are regularly tested.

• Store your backups separately. Backups should be isolated from network connections that could enable the spread of ransomware. It is important that backups be maintained offline as many ransomware variants attempt to find and encrypt or delete accessible backups. Maintaining current backups offline is critical because if your network data is encrypted with ransomware, your organization can restore systems to its previous state. Best practice is to store your backups on a separate device that cannot be accessed from a network, such as on an external hard drive.

• Maintain regularly updated “gold images” of critical systems in the event they need to be rebuilt. This entails maintaining image “templates” that include a preconfigured operating system (OS) and associated software applications that can be quickly deployed to rebuild a system, such as a virtual machine or server.

• Retain backup hardware to rebuild systems in the event rebuilding the primary system is not preferred. Hardware that is newer or older than the primary system can present installation or compatibility hurdles when rebuilding from images.

• Store source code or executables. It is more efficient to rebuild from system images, but some images will not install on different hardware or platforms correctly; having separate access to needed software will help in these cases.

• Ensure user and process accounts are limited through account use policies, user account control, and privileged account management. Organize access rights based on the principles of least privilege and separation of duties.

Recommended action after impact or Ransomware Attack

• Isolate the infected system. Remove the infected system from all networks, and disable the computer’s wireless, Bluetooth, and any other potential networking capabilities. Ensure all shared and networked drives are disconnected, whether wired or wireless. 

• Turn off other computers and devices. Power-off and segregate (i.e. remove from the network) the infected computer(s). Power-off and segregate any other computers or devices that shared a network with the infected computer(s) that have not been fully encrypted by ransomware. If possible, collect and secure all infected and potentially infected computers and devices in a central location, making sure to clearly label any computers that have been encrypted. Powering-off and segregating infected computers and computers that have not been fully encrypted may allow for the recovery of partially encrypted files by specialists.

• Secure your backups. Ensure that your backup data is offline and secure. If possible, scan your backup data with an antivirus program to check that it is free of malware.