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name: custom-signatures description: Create and deploy custom IOCs, YARA rules, Sigma rules, and STIX indicators for THOR scans.

Custom Signatures Skill

Goal: Help users create, format, and deploy custom detection content for THOR.

Overview

THOR processes all files in the ./custom-signatures folder. The file extension and filename tags determine how each file is interpreted:

Simple IOCs

Filename tags determine IOC type. Tag is detected via regex \Wc2\W (word boundary match).

Rules

YARA Rules

• Generic rules: Applied to files, process memory, DeepDive chunks
• Specific rules (tag in filename):
  • registry - Registry key/value detection
  • log - Log file and eventlog detection
  • process or memory - Process memory only
  • keyword - All string checks across modules
  • meta - All files (first 2KB + externals only)

Sigma Rules

Applied to Windows Eventlogs and log files. By default only high and critical levels shown.

STIX v2

Supports file observables (name, path, hashes, size, timestamps) and registry key observables.

THOR-Specific YARA Enhancements

Score Attribute

Copymeta:
    score = 80  // Default is 75 if not specified

External Variables

Available in generic and meta YARA rules:

Restriction Attributes

Copymeta:
    type = "memory"      // or "file" - restrict to memory/file only
    limit = "Mutex"      // Restrict to specific module
    nodeepdive = 1       // Exclude from DeepDive
    falsepositive = 1    // Reduce score instead of add

Reference Documentation

• Simple IOCs - Hash, filename, C2, keyword IOC formats
• YARA Rules - Generic and specific YARA rules for THOR
• Sigma Rules - Log detection with Sigma
• STIX IOCs - STIX v2 indicator format

Examples

• examples/hash-iocs.md - Hash IOC file examples
• examples/filename-iocs.md - Filename/path IOC patterns
• examples/yara-enhanced.md - YARA rules with THOR externals

Quick Reference

File Naming

Copy# Good - tag detected
case22-c2-domains.txt       ✓ (c2 tag)
misp-export-hashes.txt      ✓ (hashes tag)
incident-filename-iocs.txt  ✓ (filename tag)

# Bad - tag not detected
myc2iocs.txt                ✗ (no word boundary)
filenameiocs.txt            ✗ (no word boundary)

Deployment

Copy# Place files in custom-signatures folder
cp my-hashes.txt /path/to/thor/custom-signatures/

# For YARA rules, use yara subfolder
cp my-rules.yar /path/to/thor/custom-signatures/yara/

# Encrypt sensitive IOCs (optional)
thor-util encrypt --file my-c2-domains.txt
# Creates my-c2-domains.dat

Testing

Copy# Run with custom signatures only
./thor-macosx --customonly -p /target/path

# Verify IOC loading in startup
./thor-macosx 2>&1 | grep -i "custom\|ioc\|signature"