Rook Ransomware: In-Depth Analysis, Detection, Mitigation, and Removal

Summary of Rook Ransomware

Rook first emerged in November of 2021. Rook targets corporate networks and engages in multi- extortion – demanding payment for decryption tools, as well as for the non-release of stolen data. Rook ransomware payloads are partially derived from the leaked Babuk source code.

Rook Ransomware

What Does Rook Ransomware Target?

Rook ransomware targets large enterprises in a range of industries, including healthcare, education, government, financial services, retail, and manufacturing.  Rook limits or discourages targeting of entities in the CIS (Commonwealth of Independant States).

How Does Rook Ransomware Spread?

Rook has been distributed via phish/email.  These malicious emails usually contain malicious attachments, or links to payloads on malicious sites. Operators of Rook ransomware have also utilized Cobalt Strike to distribute the payloads.

Rook Ransomware Technical Details

Rook ransomware is primarily delivered via a third-party framework, for example Cobalt Strike. However, delivery via phishing email has also been reported in the wild.

Individual samples are typically UPX packed, although alternate packers have been observed such as VMProtect.  There is extensive Babuk code reused in Rook (stemming from the prior Babuk source code leaks). Many operations around host information discovery are accomplished via Babuk code reuse (e.g., enumeration of running processes, discovery of services and processes to terminate)

Upon execution, Rook launches  a command window for steaming output. This output will vary per payload. For example, some versions show the output path for kph.sys (a component of Process Hacker), while others display inaccurate information around the use of ADS (Alternate Data Streams).

The ransomware attempts to terminate any process that may interfere with encryption. Attackers have been known to leverage the kph.sys driver from Process Hacker for process termination in some cases but not all. Rook will attempt to delete volume shadow copies to prevent victims from restoring. This is achieved via vssadmin.exe.

How to Detect Rook Ransomware

  • The SentinelOne Singularity XDR Platform can identify and stop any malicious activities and items related to Rook.

In case you do not have SentinelOne deployed, detecting this ransomware requires a combination of technical and operational measures, which are designed to identify and flag suspicious activity on the network. This allows the organization to take appropriate action, and to prevent or mitigate the impact of the ransomware attack.

  1. Use antimalware software, or other security tools, which are capable of detecting and blocking known ransomware variants. These tools may use signatures, heuristics, or machine learning algorithms, to identify and block suspicious files or activities.
  2. Monitor network traffic, and look for indicators of compromise, such as unusual network traffic patterns, or communication with known command-and-control servers.
  3. Conduct regular security audits and assessments, to identify vulnerabilities in the network and the system, and to ensure that all security controls are in place and functioning properly.
  4. Educate and train employees on cybersecurity best practices, including how to identify and report suspicious emails, or other threats.
  5. Implement a robust backup and recovery plan, to ensure that the organization has a copy of its data, and can restore it in case of an attack.

How to Mitigate Rook Ransomware

  • The SentinelOne Singularity XDR Platform can return systems to their original state using either the Repair or Rollback feature.

If you do not have SentinelOne deployed, there are several steps that organizations can take to mitigate the risk of Rook ransomware attacks.

Educate Employees

Employees should be educated on the risks of ransomware, and on how to identify and avoid phishing emails, malicious attachments, and other threats. They should be encouraged to report suspicious emails or attachments, and to avoid opening them, or clicking on links or buttons in them.

Implement Strong Passwords

Organizations should implement strong, unique passwords for all user accounts, and should regularly update and rotate these passwords. Passwords should be at least 8 characters long, and should include a combination of uppercase and lowercase letters, numbers, and special characters.

Enable Multi-factor Authentication

Organizations should enable multi-factor authentication (MFA) for all user accounts, to provide an additional layer of security. This can be done through the use of mobile apps, such as Google Authenticator or Microsoft Authenticator, or through the use of physical tokens or smart cards.

Update and Patch Systems

Organizations should regularly update and patch their systems, to fix any known vulnerabilities, and to prevent attackers from exploiting them. This includes updating the operating system, applications, and firmware on all devices, as well as disabling any unnecessary or unused services or protocols.

Implement Backup and Disaster Recovery

Organizations should implement regular backup and disaster recovery (BDR) processes, to ensure that they can recover from ransomware attacks, or other disasters. This includes creating regular backups of all data and systems, and storing these backups in a secure, offsite location.

The backups should be tested regularly, to ensure that they are working, and that they can be restored quickly and easily.

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