[ATT&CKs & TTPs] Cobalt Strike: Understanding Ransomware's Favorite Tool

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Security Engineer
Apr 6, 2023
Howdy fellow IT nerds!

I recently read a digital forensics and incident response (DFIR) report discussing a ransomware attack where Cobalt Strike Beacons (CSB) played a significant role in post-exploitation activities. It seems like the majority of ransomware-related DFIR reports mention Cobalt Strike at some point. With that in mind, I think it's necessary for us to have a basic understanding of what Cobalt Strike Beacons are and their functionality.

Originally developed for penetration testers, Cobalt Strike has increasingly been adopted by ransomware operators for carrying out various tasks following initial access. The statistics alone highlight its prevalence in modern cyber attacks. Some metrics suggest that Cobalt Strike is associated with a staggering two-thirds of ransomware attacks.

Cobalt Strike is a commercial, post-exploitation framework intended to emulate real-world adversaries. Similar techniques are often employed by advanced persistent threats (APTs). Its primary component, Beacon, is a powerful, lightweight, versatile, and modular backdoor that facilitates command and control (C2) communication, lateral movement, and other post-exploitation tasks. Notable features include:
  • Communication channels: Beacon can communicate over multiple protocols, such as HTTP, HTTPS, DNS, and SMB, making it harder for defenders to detect its presence.
  • Payload delivery: Cobalt Strike can create various types of payloads, including executables, DLLs, and even Office macros, to deliver the Beacon implant.
  • Lateral movement: Beacon can use built-in tools or third-party utilities like PowerShell Empire or Mimikatz to propagate within a compromised network.
  • Anti-detection: Beacon is customizable, allowing attackers to change its behavior and signatures to evade detection by security products.
One reason for the widespread adoption of Cobalt Strike among threat actors is its ease of use and flexibility. The framework provides a wide range of tools and options, enabling attackers to tailor their activities to specific targets and network environments. Moreover, the availability of cracked versions of Cobalt Strike on the dark web has made it more accessible to threat actors and criminals.

Regardless of what specific IT role we have internally, I think it is a good idea to have a basic understanding of the capabilities of CSB and strategies to defend against its use. Generally speaking, these are the areas of focus for defense:
  • Network segmentation: Implement proper network segmentation to minimize the potential impact of lateral movement.
  • Patch management: Regularly update and patch software and operating systems to reduce the attack surface.
  • Endpoint protection: Use advanced endpoint protection solutions to detect and prevent malware and other malicious activities.
  • User education: Train users on cybersecurity best practices, such as avoiding phishing emails, to reduce the risk of initial compromise.
  • Network monitoring: Implement network monitoring and intrusion detection systems (IDS) to identify and respond to potential threats.

Further Discussion:​

  • From the protocol list above, which communication channel scares you the most in terms of detection?
  • Do you have any first-hand experience with Cobalt Strike Beacons?
  • What tools have you repeatedly seen used in attacks?