322 lines
9.9 KiB
Python
322 lines
9.9 KiB
Python
"""Elastic Detection Rules import service.
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Downloads the Elastic detection-rules repository ZIP from GitHub, parses
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every ``.toml`` rule file under ``rules/``, extracts MITRE ATT&CK
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mappings, and creates :class:`DetectionRule` records in the database.
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Strategy
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--------
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1. Download the full repo as a ZIP archive.
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2. Extract into a temporary directory.
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3. Walk all ``.toml`` files under ``rules/``.
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4. Parse each TOML file — extract rule name, description, query (KQL),
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severity, and MITRE ATT&CK threat mappings.
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5. Create / skip ``DetectionRule`` rows keyed by ``(source, source_id)``.
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6. Clean up.
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Idempotency
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-----------
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Running the import twice does **not** create duplicates. Existing
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rules are identified by ``source = "elastic"`` + ``source_id`` (the
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TOML filename).
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"""
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import io
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import logging
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import shutil
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import tempfile
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import zipfile
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from datetime import datetime
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from pathlib import Path
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import requests as _requests
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from sqlalchemy.orm import Session
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from app.models.detection_rule import DetectionRule
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from app.models.data_source import DataSource
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from app.services.audit_service import log_action
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logger = logging.getLogger(__name__)
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# ---------------------------------------------------------------------------
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# Constants
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# ---------------------------------------------------------------------------
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ELASTIC_ZIP_URL = (
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"https://github.com/elastic/detection-rules"
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"/archive/refs/heads/main.zip"
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)
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_DOWNLOAD_TIMEOUT = 300
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_ZIP_ROOT_PREFIX = "detection-rules-main"
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# Severity normalisation
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_SEVERITY_MAP = {
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"informational": "informational",
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"low": "low",
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"medium": "medium",
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"high": "high",
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"critical": "critical",
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}
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# ---------------------------------------------------------------------------
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# Internal helpers
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# ---------------------------------------------------------------------------
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def _download_zip(url: str = ELASTIC_ZIP_URL) -> bytes:
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"""Download the Elastic Detection Rules ZIP and return raw bytes."""
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logger.info("Downloading Elastic Detection Rules ZIP from %s …", url)
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resp = _requests.get(url, timeout=_DOWNLOAD_TIMEOUT, stream=True)
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resp.raise_for_status()
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content = resp.content
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logger.info("Downloaded %.1f MB", len(content) / (1024 * 1024))
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return content
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def _extract_zip(zip_bytes: bytes, dest: str) -> Path:
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"""Extract *zip_bytes* into *dest* and return rules/ dir."""
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with zipfile.ZipFile(io.BytesIO(zip_bytes)) as zf:
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zf.extractall(dest)
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rules_dir = Path(dest) / _ZIP_ROOT_PREFIX / "rules"
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if not rules_dir.is_dir():
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raise FileNotFoundError(
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f"Expected rules directory not found at {rules_dir}"
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)
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return rules_dir
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def _parse_toml_safe(path: Path) -> dict | None:
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"""Parse a TOML file. Uses the ``toml`` library."""
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try:
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import toml
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with open(path, "r", encoding="utf-8") as fh:
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return toml.load(fh)
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except Exception as exc:
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logger.debug("Failed to parse %s: %s", path, exc)
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return None
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def _extract_mitre_techniques(threat_list: list) -> list[str]:
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"""Extract MITRE technique IDs from Elastic's ``rule.threat`` array.
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Each entry looks like::
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[[rule.threat]]
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framework = "MITRE ATT&CK"
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[rule.threat.tactic]
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name = "Credential Access"
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id = "TA0006"
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[[rule.threat.technique]]
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name = "OS Credential Dumping"
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id = "T1003"
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[[rule.threat.technique.subtechnique]]
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name = "LSASS Memory"
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id = "T1003.001"
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"""
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technique_ids = []
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if not isinstance(threat_list, list):
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return technique_ids
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for threat_entry in threat_list:
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if not isinstance(threat_entry, dict):
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continue
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# Skip non-MITRE frameworks
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framework = threat_entry.get("framework", "")
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if "MITRE" not in str(framework).upper():
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continue
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techniques = threat_entry.get("technique", [])
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if not isinstance(techniques, list):
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continue
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for tech in techniques:
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if not isinstance(tech, dict):
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continue
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tech_id = tech.get("id", "")
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if tech_id and str(tech_id).upper().startswith("T"):
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technique_ids.append(str(tech_id).upper())
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# Check subtechniques
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subtechniques = tech.get("subtechnique", [])
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if isinstance(subtechniques, list):
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for subtech in subtechniques:
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if isinstance(subtech, dict):
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sub_id = subtech.get("id", "")
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if sub_id and str(sub_id).upper().startswith("T"):
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technique_ids.append(str(sub_id).upper())
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return list(set(technique_ids))
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def _parse_elastic_rules(rules_dir: Path) -> list[dict]:
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"""Walk the rules directory and parse all TOML files.
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Returns a flat list of dicts, one per (rule, technique) combination.
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"""
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results: list[dict] = []
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toml_files = sorted(rules_dir.rglob("*.toml"))
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logger.info("Found %d TOML files to parse", len(toml_files))
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for toml_path in toml_files:
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data = _parse_toml_safe(toml_path)
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if not data:
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continue
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rule = data.get("rule", {})
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if not isinstance(rule, dict):
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continue
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name = rule.get("name", "").strip()
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if not name:
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continue
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# Extract MITRE technique IDs
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threat_list = rule.get("threat", [])
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technique_ids = _extract_mitre_techniques(threat_list)
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if not technique_ids:
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continue
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description = rule.get("description", "")
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query = rule.get("query", "")
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severity = _SEVERITY_MAP.get(str(rule.get("severity", "")).lower())
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rule_type = rule.get("type", "query") # query, eql, threshold, etc.
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# Determine rule format based on type
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if rule_type == "eql":
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rule_format = "eql"
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elif rule_type == "esql":
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rule_format = "esql"
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else:
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rule_format = "kql"
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# Use filename as source_id
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source_id = toml_path.name
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# Read raw content
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try:
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with open(toml_path, "r", encoding="utf-8") as fh:
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raw_content = fh.read()
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except Exception:
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raw_content = query or str(data)
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# Build source URL
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relative = str(toml_path.relative_to(rules_dir.parent)).replace("\\", "/")
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source_url = (
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f"https://github.com/elastic/detection-rules/blob/main/{relative}"
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)
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# One entry per technique
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for tech_id in technique_ids:
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results.append({
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"mitre_technique_id": tech_id,
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"title": name[:500],
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"description": str(description)[:2000] if description else None,
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"source_id": source_id,
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"source_url": source_url,
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"rule_content": query[:50000] if query else raw_content[:50000],
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"rule_format": rule_format,
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"severity": severity,
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"platforms": _infer_platforms(rules_dir, toml_path),
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})
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logger.info("Parsed %d (rule, technique) pairs total", len(results))
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return results
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def _infer_platforms(rules_dir: Path, toml_path: Path) -> list[str] | None:
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"""Infer platforms from the rule's directory structure.
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Elastic organizes rules by OS: rules/windows/, rules/linux/, etc.
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"""
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relative = toml_path.relative_to(rules_dir)
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parts = [p.lower() for p in relative.parts]
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platforms = []
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if "windows" in parts:
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platforms.append("windows")
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if "linux" in parts:
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platforms.append("linux")
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if "macos" in parts:
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platforms.append("macos")
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return platforms if platforms else None
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# ---------------------------------------------------------------------------
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# Public API
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# ---------------------------------------------------------------------------
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def sync(db: Session) -> dict:
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"""Download and import Elastic detection rules.
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Returns a summary dict with ``created``, ``skipped_existing``, ``total_parsed``.
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"""
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tmp_dir = tempfile.mkdtemp(prefix="aegis_elastic_")
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try:
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zip_bytes = _download_zip()
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rules_dir = _extract_zip(zip_bytes, tmp_dir)
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parsed_rules = _parse_elastic_rules(rules_dir)
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finally:
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shutil.rmtree(tmp_dir, ignore_errors=True)
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logger.info("Cleaned up temp directory %s", tmp_dir)
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# Pre-load existing source_ids for dedup
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existing_ids: set[str] = {
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row[0]
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for row in db.query(DetectionRule.source_id)
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.filter(DetectionRule.source == "elastic")
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.filter(DetectionRule.source_id.isnot(None))
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.all()
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}
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created = 0
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skipped = 0
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for item in parsed_rules:
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if item["source_id"] in existing_ids:
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skipped += 1
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continue
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rule = DetectionRule(
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mitre_technique_id=item["mitre_technique_id"],
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title=item["title"],
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description=item["description"],
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source="elastic",
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source_id=item["source_id"],
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source_url=item["source_url"],
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rule_content=item["rule_content"],
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rule_format=item["rule_format"],
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severity=item["severity"],
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platforms=item["platforms"],
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is_active=True,
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)
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db.add(rule)
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existing_ids.add(item["source_id"])
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created += 1
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db.commit()
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summary = {
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"created": created,
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"skipped_existing": skipped,
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"total_parsed": len(parsed_rules),
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}
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# Update DataSource record
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ds = db.query(DataSource).filter(DataSource.name == "elastic_rules").first()
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if ds:
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ds.last_sync_at = datetime.utcnow()
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ds.last_sync_status = "success"
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ds.last_sync_stats = summary
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db.commit()
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logger.info("Elastic import complete — %s", summary)
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log_action(db, user_id=None, action="import_elastic_rules",
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entity_type="detection_rule", entity_id=None, details=summary)
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return summary
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