350 lines
11 KiB
Python
350 lines
11 KiB
Python
"""Sigma Rules import service.
|
|
|
|
Downloads the SigmaHQ repository ZIP from GitHub, parses every YAML rule
|
|
file under ``rules/``, extracts MITRE ATT&CK tags, and creates
|
|
:class:`DetectionRule` records in the database.
|
|
|
|
Strategy
|
|
--------
|
|
1. Download the full SigmaHQ repo as a ZIP archive.
|
|
2. Extract in a temporary directory.
|
|
3. Walk all ``.yml`` files under ``rules/``.
|
|
4. Parse each YAML file — extract title, description, logsource,
|
|
detection tags, severity (``level``), and the raw YAML content.
|
|
5. Filter: only import rules that have at least one ``attack.tXXXX`` tag.
|
|
6. Create / skip ``DetectionRule`` rows keyed by ``(source, source_id)``.
|
|
7. Clean up the temporary directory.
|
|
|
|
Idempotency
|
|
-----------
|
|
Running the import twice does **not** create duplicates. Existing
|
|
rules are identified by ``source = "sigma"`` + ``source_id`` (relative
|
|
file path) and simply skipped.
|
|
"""
|
|
|
|
import io
|
|
import logging
|
|
import re
|
|
import shutil
|
|
import tempfile
|
|
import zipfile
|
|
from datetime import datetime
|
|
from pathlib import Path
|
|
|
|
import requests as _requests
|
|
import yaml
|
|
from sqlalchemy.orm import Session
|
|
|
|
from app.models.detection_rule import DetectionRule
|
|
from app.models.data_source import DataSource
|
|
from app.services.audit_service import log_action
|
|
|
|
logger = logging.getLogger(__name__)
|
|
|
|
# ---------------------------------------------------------------------------
|
|
# Constants
|
|
# ---------------------------------------------------------------------------
|
|
|
|
SIGMA_ZIP_URL = (
|
|
"https://github.com/SigmaHQ/sigma/archive/refs/heads/master.zip"
|
|
)
|
|
|
|
_DOWNLOAD_TIMEOUT = 300
|
|
_ZIP_ROOT_PREFIX = "sigma-master"
|
|
|
|
# Regex to extract MITRE ATT&CK technique IDs from Sigma tags
|
|
# e.g. "attack.t1059.001" → "T1059.001"
|
|
_ATTACK_TAG_RE = re.compile(r"attack\.(t\d{4}(?:\.\d{3})?)", re.IGNORECASE)
|
|
|
|
# Sigma severity levels
|
|
_SEVERITY_MAP = {
|
|
"informational": "informational",
|
|
"low": "low",
|
|
"medium": "medium",
|
|
"high": "high",
|
|
"critical": "critical",
|
|
}
|
|
|
|
|
|
# ---------------------------------------------------------------------------
|
|
# Internal helpers
|
|
# ---------------------------------------------------------------------------
|
|
|
|
|
|
def _download_zip(url: str = SIGMA_ZIP_URL) -> bytes:
|
|
"""Download the SigmaHQ ZIP and return raw bytes."""
|
|
logger.info("Downloading SigmaHQ ZIP from %s …", url)
|
|
resp = _requests.get(url, timeout=_DOWNLOAD_TIMEOUT, stream=True)
|
|
resp.raise_for_status()
|
|
content = resp.content
|
|
logger.info("Downloaded %.1f MB", len(content) / (1024 * 1024))
|
|
return content
|
|
|
|
|
|
def _safe_extract_zip(zip_bytes: bytes, dest: str) -> None:
|
|
"""Extract *zip_bytes* into *dest* with Zip Slip and Zip Bomb protection.
|
|
|
|
Raises :class:`ValueError` if any member tries to escape the target
|
|
directory (path traversal / Zip Slip) or if the archive exceeds the
|
|
safety limits.
|
|
"""
|
|
# Maximum uncompressed size: 500 MB — prevents zip-bomb DoS
|
|
_MAX_UNCOMPRESSED_SIZE = 500 * 1024 * 1024
|
|
# Maximum number of entries
|
|
_MAX_ENTRIES = 50_000
|
|
|
|
dest_path = Path(dest).resolve()
|
|
|
|
with zipfile.ZipFile(io.BytesIO(zip_bytes)) as zf:
|
|
entries = zf.infolist()
|
|
|
|
if len(entries) > _MAX_ENTRIES:
|
|
raise ValueError(
|
|
f"ZIP archive contains {len(entries)} entries "
|
|
f"(limit: {_MAX_ENTRIES}) — possible zip bomb"
|
|
)
|
|
|
|
total_size = sum(info.file_size for info in entries)
|
|
if total_size > _MAX_UNCOMPRESSED_SIZE:
|
|
raise ValueError(
|
|
f"ZIP uncompressed size {total_size / (1024 * 1024):.0f} MB "
|
|
f"exceeds limit of {_MAX_UNCOMPRESSED_SIZE / (1024 * 1024):.0f} MB"
|
|
)
|
|
|
|
for member in entries:
|
|
target = (dest_path / member.filename).resolve()
|
|
if not target.is_relative_to(dest_path):
|
|
raise ValueError(
|
|
f"Zip Slip detected — member '{member.filename}' "
|
|
f"resolves outside target directory"
|
|
)
|
|
|
|
zf.extractall(dest)
|
|
|
|
|
|
def _extract_zip(zip_bytes: bytes, dest: str) -> Path:
|
|
"""Extract *zip_bytes* into *dest* and return the path to rules/ dir."""
|
|
_safe_extract_zip(zip_bytes, dest)
|
|
rules_dir = Path(dest) / _ZIP_ROOT_PREFIX / "rules"
|
|
if not rules_dir.is_dir():
|
|
raise FileNotFoundError(
|
|
f"Expected rules directory not found at {rules_dir}"
|
|
)
|
|
return rules_dir
|
|
|
|
|
|
def _extract_attack_tags(tags: list) -> list[str]:
|
|
"""Extract MITRE technique IDs from Sigma tag list.
|
|
|
|
Example input: ["attack.defense_evasion", "attack.t1059.001", "cve.2021.44228"]
|
|
Example output: ["T1059.001"]
|
|
"""
|
|
technique_ids = []
|
|
for tag in tags:
|
|
m = _ATTACK_TAG_RE.match(str(tag).strip())
|
|
if m:
|
|
technique_ids.append(m.group(1).upper())
|
|
return list(set(technique_ids))
|
|
|
|
|
|
def _parse_sigma_rules(rules_dir: Path) -> list[dict]:
|
|
"""Walk the rules directory and parse all Sigma YAML files.
|
|
|
|
Returns a flat list of dicts, one per (rule, technique) combination.
|
|
A single Sigma rule tagged with N techniques produces N entries.
|
|
"""
|
|
results: list[dict] = []
|
|
yaml_files = sorted(rules_dir.rglob("*.yml"))
|
|
logger.info("Found %d YAML files to parse", len(yaml_files))
|
|
|
|
for yaml_path in yaml_files:
|
|
relative_path = str(yaml_path.relative_to(rules_dir.parent))
|
|
try:
|
|
with open(yaml_path, "r", encoding="utf-8") as fh:
|
|
data = yaml.safe_load(fh)
|
|
except Exception as exc:
|
|
logger.debug("Failed to parse %s: %s", yaml_path, exc)
|
|
continue
|
|
|
|
if not isinstance(data, dict):
|
|
continue
|
|
|
|
title = data.get("title", "").strip()
|
|
if not title:
|
|
continue
|
|
|
|
# Extract ATT&CK technique IDs from tags
|
|
tags = data.get("tags", [])
|
|
if not isinstance(tags, list):
|
|
continue
|
|
|
|
technique_ids = _extract_attack_tags(tags)
|
|
if not technique_ids:
|
|
continue # Skip rules without ATT&CK mapping
|
|
|
|
description = data.get("description", "")
|
|
level = str(data.get("level", "")).lower()
|
|
severity = _SEVERITY_MAP.get(level)
|
|
|
|
# Extract logsource
|
|
logsource = data.get("logsource", {})
|
|
if not isinstance(logsource, dict):
|
|
logsource = {}
|
|
|
|
# Read full YAML content for storage
|
|
try:
|
|
with open(yaml_path, "r", encoding="utf-8") as fh:
|
|
raw_content = fh.read()
|
|
except Exception:
|
|
raw_content = yaml.dump(data, default_flow_style=False)
|
|
|
|
# False positive assessment
|
|
falsepositives = data.get("falsepositives", [])
|
|
if isinstance(falsepositives, list) and len(falsepositives) > 3:
|
|
fp_rate = "high"
|
|
elif isinstance(falsepositives, list) and len(falsepositives) > 1:
|
|
fp_rate = "medium"
|
|
else:
|
|
fp_rate = "low"
|
|
|
|
# Create one entry per technique
|
|
for tech_id in technique_ids:
|
|
source_url = (
|
|
f"https://github.com/SigmaHQ/sigma/blob/master/"
|
|
f"{relative_path.replace(chr(92), '/')}"
|
|
)
|
|
results.append({
|
|
"mitre_technique_id": tech_id,
|
|
"title": title[:500],
|
|
"description": str(description)[:2000] if description else None,
|
|
"source_id": relative_path,
|
|
"source_url": source_url,
|
|
"rule_content": raw_content,
|
|
"severity": severity,
|
|
"log_sources": logsource if logsource else None,
|
|
"false_positive_rate": fp_rate,
|
|
"platforms": _platforms_from_logsource(logsource),
|
|
})
|
|
|
|
logger.info("Parsed %d (rule, technique) pairs total", len(results))
|
|
return results
|
|
|
|
|
|
def _platforms_from_logsource(logsource: dict) -> list[str]:
|
|
"""Infer platform list from Sigma logsource."""
|
|
platforms = []
|
|
product = str(logsource.get("product", "")).lower()
|
|
service = str(logsource.get("service", "")).lower()
|
|
|
|
if "windows" in product or "windows" in service:
|
|
platforms.append("windows")
|
|
if "linux" in product or "linux" in service:
|
|
platforms.append("linux")
|
|
if "macos" in product or "macos" in service:
|
|
platforms.append("macos")
|
|
|
|
# Sysmon → Windows
|
|
if "sysmon" in service and "windows" not in platforms:
|
|
platforms.append("windows")
|
|
|
|
return platforms if platforms else None
|
|
|
|
|
|
# ---------------------------------------------------------------------------
|
|
# Public API
|
|
# ---------------------------------------------------------------------------
|
|
|
|
|
|
def sync(db: Session) -> dict:
|
|
"""Download and import Sigma detection rules.
|
|
|
|
Parameters
|
|
----------
|
|
db : Session
|
|
Active SQLAlchemy database session.
|
|
|
|
Returns
|
|
-------
|
|
dict
|
|
Summary with ``created``, ``skipped_existing``, ``total_parsed``.
|
|
"""
|
|
tmp_dir = tempfile.mkdtemp(prefix="aegis_sigma_")
|
|
try:
|
|
zip_bytes = _download_zip()
|
|
rules_dir = _extract_zip(zip_bytes, tmp_dir)
|
|
parsed_rules = _parse_sigma_rules(rules_dir)
|
|
finally:
|
|
shutil.rmtree(tmp_dir, ignore_errors=True)
|
|
logger.info("Cleaned up temp directory %s", tmp_dir)
|
|
|
|
# Pre-load existing source_ids for dedup
|
|
existing_ids: set[str] = {
|
|
row[0]
|
|
for row in db.query(DetectionRule.source_id)
|
|
.filter(DetectionRule.source == "sigma")
|
|
.filter(DetectionRule.source_id.isnot(None))
|
|
.all()
|
|
}
|
|
|
|
created = 0
|
|
skipped = 0
|
|
|
|
for item in parsed_rules:
|
|
# Dedup key: source_id (relative path). A rule file may produce
|
|
# multiple entries (one per technique), but we deduplicate by
|
|
# source_id so re-runs are safe. For multi-technique rules we
|
|
# only skip if the exact same source_id is already present.
|
|
dedup_key = f"{item['source_id']}::{item['mitre_technique_id']}"
|
|
if item["source_id"] in existing_ids:
|
|
skipped += 1
|
|
continue
|
|
|
|
rule = DetectionRule(
|
|
mitre_technique_id=item["mitre_technique_id"],
|
|
title=item["title"],
|
|
description=item["description"],
|
|
source="sigma",
|
|
source_id=item["source_id"],
|
|
source_url=item["source_url"],
|
|
rule_content=item["rule_content"],
|
|
rule_format="sigma_yaml",
|
|
severity=item["severity"],
|
|
platforms=item["platforms"],
|
|
log_sources=item["log_sources"],
|
|
false_positive_rate=item["false_positive_rate"],
|
|
is_active=True,
|
|
)
|
|
db.add(rule)
|
|
existing_ids.add(item["source_id"])
|
|
created += 1
|
|
|
|
db.commit()
|
|
|
|
summary = {
|
|
"created": created,
|
|
"skipped_existing": skipped,
|
|
"total_parsed": len(parsed_rules),
|
|
}
|
|
|
|
# Update DataSource record
|
|
ds = db.query(DataSource).filter(DataSource.name == "sigma").first()
|
|
if ds:
|
|
ds.last_sync_at = datetime.utcnow()
|
|
ds.last_sync_status = "success"
|
|
ds.last_sync_stats = summary
|
|
db.commit()
|
|
|
|
logger.info("Sigma import complete — %s", summary)
|
|
|
|
log_action(
|
|
db,
|
|
user_id=None,
|
|
action="import_sigma_rules",
|
|
entity_type="detection_rule",
|
|
entity_id=None,
|
|
details=summary,
|
|
)
|
|
db.commit()
|
|
|
|
return summary
|