withsecureopensource/chainsawRapidly Search and Hunt through Windows Forensic Artefacts
Chainsaw provides a powerful ‘first-response’ capability to quickly identify threats within Windows forensic artefacts such as Event Logs and the MFT file. Chainsaw offers a generic and fast method of searching through event logs for keywords, and by identifying threats using built-in support for Sigma detection rules, and via custom Chainsaw detection rules.
Extended information can be found in the Wiki for this tool: https://github.com/WithSecureLabs/chainsaw/wiki
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 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.
Using the --sigma and --mapping parameters you can specify a directory containing a subset of SIGMA detection rules (or just the entire SIGMA git repo) and chainsaw will automatically load, convert and run these rules against the provided event logs. The mapping file tells chainsaw which fields in the event logs to use for rule matching. By default, Chainsaw supports a wide range of Event Log types, including but not limited to:
| Event Type | Event ID |
|---|---|
| Process Creation (Sysmon) | 1 |
| Network Connections (Sysmon) | 3 |
| Image Loads (Sysmon) | 7 |
| File Creation (Sysmon) | 11 |
| Registry Events (Sysmon) | 13 |
| Powershell Script Blocks | 4104 |
| Process Creation | 4688 |
| Scheduled Task Creation | 4698 |
| Service Creation | 7045 |
See the mapping file for the full list of fields that are used for rule detection, and feel free to extend it to your needs.
In addition to supporting sigma rules, Chainsaw also supports a custom rule format. In the repository you will find a rules directory that contains various Chainsaw rules that allows users to:
With the release of Chainsaw v2, we decided to no longer include the Sigma Rules and EVTX-Attack-Samples repositories as Chainsaw submodules. We recommend that you clone these repositories separately to ensure you have the latest versions.
If you still need an all-in-one package containing the Chainsaw binary, Sigma rules and example Event logs, you can download it from the releases section of this GitHub repo. In this releases section you will also find pre-compiled binary-only versions of Chainsaw for various platforms and architectures.
If you want to compile Chainsaw yourself, you can clone the Chainsaw repo:
git clone https://github.com/WithSecureLabs/chainsaw.git
and compile the code yourself by running: cargo build --release. Once the build has finished, you will find a copy of the compiled binary in the target/release folder.
Make sure to build with the --release flag as this will ensure significantly faster execution time.
If you want to quickly see what Chainsaw looks like when it runs, you can clone the Sigma Rules and EVTX-Attack-Samples repositories:
git clone https://github.com/SigmaHQ/sigma
git clone https://github.com/sbousseaden/EVTX-ATTACK-SAMPLES.git
and then run Chainsaw with the parameters below:
./chainsaw hunt EVTX-ATTACK-SAMPLES/ -s sigma/ --mapping mappings/sigma-event-logs-all.yml
├───devShells
│ └───x86_64-linux
│ └───default: development environment 'nix-shell'
├───formatter
│ └───x86_64-linux: package 'alejandra-3.1.0'
└───packages
└───x86_64-linux
├───chainsaw: package 'chainsaw-2.10.1'
└───default: package 'chainsaw-2.10.1'