Hunting EVTX with Chainsaw
Overview
Chainsaw is a fast, Rust-based forensic artifact search and hunting tool from WithSecure Labs. It provides first-response capability to rapidly identify threats within Windows Event Logs (.evtx) and other artifacts. Chainsaw can hunt with the full SigmaHQ rule corpus (translating Sigma to its internal Tau engine), run its own built-in detection rules, perform high-speed keyword/regex search across logs, and analyse specialized artifacts such as the AppCompatCache (shimcache), SRUM database, and event-log gaps. Output can be a colorized table, CSV, or JSON for downstream tooling.
Chainsaw's strength is speed and flexibility during initial triage: an analyst can drop a folder of collected EVTX onto the tool and get back a prioritized set of detections in seconds, then pivot with targeted search queries to confirm a hypothesis. Unlike a SIEM, it needs no ingestion pipeline, runs as a single binary, and works fully offline against acquired evidence — ideal for the field or an air-gapped analysis VM. The --mapping file tells Chainsaw how Sigma fields translate to Windows event fields, which is what enables broad Sigma coverage over EVTX.
A common hunt outcome is detecting suspicious PowerShell — MITRE ATT&CK T1059.001 (Command and Scripting Interpreter: PowerShell) — by running Sigma rules against PowerShell operational logs (Event ID 4104 script-block logging) or searching for encoded-command patterns. This skill maps to NIST CSF DE.AE-02 (potentially adverse events are analyzed to better understand associated activities).
When to Use
- During first-response triage to rapidly hunt threats across collected Windows event logs.
- When you need offline Sigma-based detection over
.evtx without standing up a SIEM.
- To run fast keyword/regex searches confirming or refuting a hunt hypothesis.
- To analyse shimcache, SRUM, or event-log time gaps for execution evidence and tampering.
- To produce CSV/JSON detection output for reporting or pipeline ingestion.
Prerequisites
Objectives
- Hunt collected EVTX with Sigma rules using the correct mapping file.
- Filter detections by rule level, status, and kind to reduce noise.
- Search logs by keyword, regex, and Tau expression for targeted confirmation.
- Output detections as table, CSV, and JSON.
- Analyse shimcache (with Amcache timestamp pairing), SRUM, and event-log gaps.
MITRE ATT&CK Mapping
| Technique ID | Official Name | Why Chainsaw Detects It |
|---|
| T1059.001 | Command and Scripting Interpreter: PowerShell | Sigma rules over EID 4104/4103 and search flag malicious PowerShell |
| T1059.003 | Command and Scripting Interpreter: Windows Command Shell | Process-creation Sigma rules surface suspicious cmd usage |
| T1547.001 | Boot or Logon Autostart Execution: Registry Run Keys / Startup Folder | Sigma rules over registry events flag persistence |
| T1053.005 | Scheduled Task/Job: Scheduled Task | Rules over EID 4698/106 detect task creation |
| T1070.006 | Indicator Removal: Timestomp | analyse gaps and shimcache analysis reveal tampering/time gaps |
| T1204.002 | User Execution: Malicious File | Shimcache analysis shows executed binaries |
Workflow
1. Hunt EVTX with Sigma rules
Run the SigmaHQ corpus against collected logs using the bundled mapping file. The mapping translates Sigma fields to EVTX fields.
chainsaw hunt ./collected_evtx \
-s ./sigma/rules \
--mapping ./mappings/sigma-event-logs-all.yml
2. Hunt with Chainsaw built-in rules plus Sigma
Combine Chainsaw's own rules (-r) with Sigma (-s) for broader coverage.
chainsaw hunt ./collected_evtx \
-r ./rules \
-s ./sigma/rules \
--mapping ./mappings/sigma-event-logs-all.yml
3. Filter to reduce noise
Limit results by Sigma rule level, status, and detection kind.
chainsaw hunt ./collected_evtx -s ./sigma/rules \
--mapping ./mappings/sigma-event-logs-all.yml \
--level high --status stable --kind evtx
4. Output to CSV and JSON
Write structured output for reporting and pipelines.
chainsaw hunt ./collected_evtx -s ./sigma/rules \
--mapping ./mappings/sigma-event-logs-all.yml --json > detections.json
chainsaw hunt ./collected_evtx -s ./sigma/rules \
--mapping ./mappings/sigma-event-logs-all.yml --csv --output ./csv_out
5. Targeted keyword and regex search
Confirm a hypothesis by searching raw events independent of rules.
chainsaw search "mimikatz" -i ./collected_evtx
chainsaw search -e "-[Ee]nc(odedCommand)?\s+[A-Za-z0-9+/=]{20,}" ./collected_evtx --json
chainsaw search ./collected_evtx -t 'Event.System.EventID: =4624' \
--from "2026-06-01T00:00:00" --to "2026-06-20T00:00:00"
6. Analyse shimcache for execution evidence
Parse the AppCompatCache from the SYSTEM hive, pair it with Amcache timestamps, and pattern-match suspicious entries.
chainsaw analyse shimcache ./SYSTEM \
--regexfile ./shimcache_patterns.txt \
--amcache ./Amcache.hve --tspair \
--output ./shimcache_analysis.csv
7. Analyse SRUM and event-log gaps
Detect program/network usage and identify suspicious logging gaps (possible log clearing or timestomp).
chainsaw analyse srum --software ./SOFTWARE ./SRUDB.dat -o srum.json
chainsaw analyse gaps ./collected_evtx --min-time-gap-minutes 30 --json
8. Dump and lint
Inspect raw artifact content and validate custom rules before a hunt.
chainsaw dump ./SOFTWARE --json --output dump.json
chainsaw lint -r ./rules --kind sigma
Tools and Resources
Validation Criteria
