Threat Hunting I – Understanding Threat Hunting

Although Threat Hunting is nothing new, it is a very hot topic lately. Even if you have perimeter and endpoint security devices and SIEM for collecting and correlating logs from them, it is not a good way to wait for incidents coming. Without Threat Hunting, dwell time is increasing more than 150 days, and this is not acceptable anymore. While attackers are working proactively and developing new techniques day by day, security teams need to be more proactive too. Threat Hunting is the most proactive approach in an organization’s security structure and improves its security posture.

Dwell time is the dirty metric nobody wants to talk about in cyber security. It signifies the amount of time threat actors go undetected in an environment, and the industry stats about it are staggering.
Source: Extrahop

In its simplest definition, Threat Hunting is detecting abnormal activities on endpoints and network. But, what to look for hunting threats?

What to Hunt?

Threat Hunting is a continuous process. Hunters should check anything that could be an evidence of an incident.

  • Processes: Processes are important components of OSs. Adversaries may inject malicious code into hijacked processes. Therefore, hunters should check processes and child processes regularly.
  • Binaries: Hunters should check binaries with their checksum, name and other specifications.
  • Network: Network activities to specific destinations and anomalies in network should be checked.
  • Registery: Hunters should check registery key additions and modifications.

The Team

For a continuous hunting, organizations need to have threat hunters in their CSIRT. The difference between analysts and threat hunters is the proactive approach as mentioned before. Also in smaller organizations, SOC analysts may work on threat hunting but actually, a threat hunter may has more specifications than an analyst. In larger organizations, it is important to have a dedicated threat hunting leader and team. This team should has detailed knowledge about;

  • OSs: The Threat Hunting team should have knowledge about OSs that organization is using. This knowledge must include process structures, files, permissions, and registery depending on the OS. This is important because malicious files and attackers make changes in OS here. A threat hunter need to understand what is normal and what is not. Something is not normal could be a sign of an intrusion. For having this knowledge, baselines could be created for all critical systems. These baselines will help to know the normal and the anomalies.
  • Apps: Threat Hunters should have knowledge about the applications used in the organization. It is also important to know perimeter and endpoint security devices and applications used by organization.
  • Business: Threat Hunting team should have knowledge about the organization’s business so they need to follow adversaries working on the organization’s sector and geographical location. It is also important to know third party companies the organization works and communication ways with them.
  • Network: In a big and segmented network structure, it is important to know where the critical assets are.
  • The Lockheed Martin Cyber Kill Chain: Also known as APT phases, represents the phases of an advanced attack.
  • TTPs: IoCs are important components for hunting but they provide to detect “known knowns”. TTPs are at the top of Pyramid of Pain (defined by David Bianco) and especially adversaries’ techniques and tactics should be known those are threatening the organization’s sector and location.
  • Threat Hunting Tools: In CSIRT plan, it needs to be included that which tools and techniques can be used for threat hunting. Threat hunters should have knowledge of these tools and techniques.
  • IR&H Plan: Threat hunting is only a step of proactive approach. If threat hunters successfully find an intrusion or anomaly in systems, they need to know the next step. Who should they inform? What should be done?..etc..

Requirements

  • Threat Intelligence: Threat intelligence is one of the most important feeds of threat hunting. Threat hunters need to have most recent intelligence and IoCs so they cant perform hunting the latest threats.
  • EDR: Threat hunters need IoCs but also need to know how to use these IoCs. After gathering the most recent IoCs from TI platforms, an IoC sweep must be made on endpoints.
  • NDR: Just like endpoints, network traffic also need to be checked with the latest IoCs. For doing this, CSIRT need to collect all east-west and south-north network traffic. NDR devices those have AI capabilities also detect anomalies in the network.
  • SIEM: Depending on the hunt’s scope, the threat hunter may need to check IPS/IDS, proxy, DNS, firewall or some other tools’ logs. Because logs are coming from different sources, CSIRT need to collect and correlate these logs in SIEM and feeding SIEM with the latest IoCs, these logs will more meaningful.
  • FIM: We said that baselines must be created for critical systems. FIM solutions will help CSIRT to create baselines for OSs and alert analysts when an unauthorized transaction is made.

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