Why Chainsaw?

Overview

At WithSecure Countercept, we ingest a wide range of telemetry sources from endpoints via our EDR agent to provide our managed detection and response service. However, there are circumstances where we need to quickly analyse forensic artefacts that hasn’t been captured by our EDR, a common example being incident response investigations on an estate where our EDR wasn’t installed at the time of the compromise. Chainsaw was created to provide our threat hunters and incident response consultants with a tool to perform rapid triage of forensic artefacts in these circumstances.

Windows Event Logs

Windows event logs provide a rich source of forensic information for threat hunting and incident response investigations. Unfortunately, processing and searching through event logs can be a slow and time-consuming process, and in most cases requires the overhead of surrounding infrastructure – such as an ELK stack or Splunk instance – to hunt efficiently through the log data and apply detection logic. This overhead often means that blue teams are unable to quickly triage Windows event logs to provide the direction and conclusions required to progress their investigations. Chainsaw solves the issue since it allows the rapid search and hunt through Windows event logs.

At the time of writing, there are very few open-source, standalone tools that provide a simple and fast method of triaging Windows event logs, identifying interesting elements within the logs and applying a detection logic rule format (such as Sigma) to detect signs of malicious activity. In our testing, the tools that did exist struggled to efficiently apply detection logic to large volumes of event logs making them unsuitable for scenarios where quick triage is required.