Christian Krakau-Louis
217 lines
7.3 KiB
Python
217 lines
7.3 KiB
Python
"""MTA-STS posture checks for monitored domains."""
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from __future__ import annotations
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import json
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from dataclasses import asdict, dataclass, field
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from datetime import datetime, timedelta, timezone
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from typing import Any, Dict, List, Optional, Tuple
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import httpx
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from sqlalchemy.exc import IntegrityError
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from sqlalchemy.orm import Session
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from app.models.dns_cache import DNSCache
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from app.services.dns_cache import DEFAULT_DNS_CACHE_TTL_SECONDS
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from app.services.dns_resolver import BaseDNSProvider
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_CACHE_KEY = "mta-sts-v1"
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_POLICY_TIMEOUT_SECONDS = 5.0
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_VALID_MODES = {"enforce", "testing", "none"}
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@dataclass
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class MTAStsResult:
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"""Operator-facing MTA-STS posture evidence."""
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status: str = "fail"
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dns_record: Optional[str] = None
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policy_url: Optional[str] = None
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policy_text: Optional[str] = None
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mode: Optional[str] = None
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max_age: Optional[int] = None
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mx: List[str] = field(default_factory=list)
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errors: List[str] = field(default_factory=list)
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warnings: List[str] = field(default_factory=list)
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def _utcnow_naive() -> datetime:
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return datetime.now(timezone.utc).replace(tzinfo=None)
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def _is_fresh(row: DNSCache, ttl_seconds: int, now: datetime) -> bool:
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return row.checked_at >= now - timedelta(seconds=ttl_seconds)
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def _result_from_json(value: str) -> MTAStsResult:
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data = json.loads(value)
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return MTAStsResult(
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status=str(data.get("status") or "fail"),
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dns_record=data.get("dns_record"),
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policy_url=data.get("policy_url"),
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policy_text=data.get("policy_text"),
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mode=data.get("mode"),
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max_age=data.get("max_age"),
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mx=list(data.get("mx") or []),
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errors=list(data.get("errors") or []),
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warnings=list(data.get("warnings") or []),
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)
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def parse_mta_sts_record(records: List[str]) -> Tuple[Optional[str], List[str], List[str]]:
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"""Return the selected MTA-STS TXT record, warnings, and errors."""
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sts_records = [record for record in records if record.lower().startswith("v=stsv1")]
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if not sts_records:
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return None, [], ["No _mta-sts TXT record was found."]
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warnings = []
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if len(sts_records) > 1:
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warnings.append("Multiple _mta-sts TXT records were found; publish exactly one.")
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record = sts_records[0]
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tags = {
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part.split("=", 1)[0].strip().lower(): part.split("=", 1)[1].strip()
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for part in record.split(";")
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if "=" in part
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}
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errors = []
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if tags.get("v", "").lower() != "stsv1":
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errors.append("The _mta-sts TXT record must start with v=STSv1.")
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if not tags.get("id"):
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errors.append("The _mta-sts TXT record must include a non-empty id tag.")
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return record, warnings, errors
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def parse_mta_sts_policy( # noqa: C901
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policy_text: str,
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) -> Tuple[Dict[str, Any], List[str], List[str]]:
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"""Parse and validate an MTA-STS policy file."""
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data: Dict[str, Any] = {"mx": []}
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for raw_line in policy_text.splitlines():
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line = raw_line.strip()
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if not line or line.startswith("#") or ":" not in line:
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continue
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key, value = line.split(":", 1)
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key = key.strip().lower()
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value = value.strip()
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if key == "mx":
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data.setdefault("mx", []).append(value)
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else:
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data[key] = value
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errors = []
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warnings = []
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if str(data.get("version", "")).upper() != "STSV1":
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errors.append("The policy file must contain version: STSv1.")
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mode = str(data.get("mode", "")).lower()
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if mode not in _VALID_MODES:
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errors.append("The policy file must contain mode: enforce, testing, or none.")
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elif mode in {"testing", "none"}:
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warnings.append(f"MTA-STS policy is valid but not enforcing mail delivery ({mode}).")
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try:
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max_age = int(str(data.get("max_age", "")))
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if max_age <= 0:
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errors.append("The policy max_age must be greater than zero.")
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data["max_age"] = max_age
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except ValueError:
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errors.append("The policy file must contain an integer max_age value.")
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if not data.get("mx"):
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errors.append("The policy file must contain at least one mx entry.")
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return data, warnings, errors
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async def check_mta_sts(domain: str, provider: BaseDNSProvider) -> MTAStsResult:
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"""Resolve the MTA-STS TXT record and validate the HTTPS policy file."""
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result = MTAStsResult(policy_url=f"https://mta-sts.{domain}/.well-known/mta-sts.txt")
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try:
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records = await provider.lookup_txt(f"_mta-sts.{domain}")
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except LookupError as exc:
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result.errors.append(f"MTA-STS DNS lookup failed: {exc}")
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return result
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record, warnings, errors = parse_mta_sts_record(records)
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result.dns_record = record
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result.warnings.extend(warnings)
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result.errors.extend(errors)
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if record is None:
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return result
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try:
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async with httpx.AsyncClient(
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timeout=_POLICY_TIMEOUT_SECONDS, follow_redirects=False
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) as client:
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response = await client.get(result.policy_url)
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response.raise_for_status()
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result.policy_text = response.text
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except (httpx.RequestError, httpx.HTTPStatusError, httpx.TimeoutException) as exc:
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result.errors.append(f"MTA-STS policy fetch failed: {exc}")
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return result
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policy, policy_warnings, policy_errors = parse_mta_sts_policy(result.policy_text or "")
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result.warnings.extend(policy_warnings)
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result.errors.extend(policy_errors)
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result.mode = policy.get("mode")
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result.max_age = policy.get("max_age")
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result.mx = list(policy.get("mx") or [])
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result.status = "pass" if not result.errors else "fail"
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return result
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async def check_mta_sts_cached(
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db: Session,
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provider: BaseDNSProvider,
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domain: str,
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*,
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ttl_seconds: int = DEFAULT_DNS_CACHE_TTL_SECONDS,
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refresh: bool = False,
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) -> Tuple[MTAStsResult, bool, datetime]:
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"""Resolve MTA-STS posture, reusing the shared DNS cache semantics."""
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now = _utcnow_naive()
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provider_name = f"{provider.__class__.__name__}:mta-sts"
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row = (
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db.query(DNSCache)
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.filter(
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DNSCache.domain == domain,
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DNSCache.provider == provider_name,
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DNSCache.selectors_key == _CACHE_KEY,
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)
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.first()
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)
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if row and not refresh and _is_fresh(row, ttl_seconds, now):
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return _result_from_json(row.result_json), True, row.checked_at
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result = await check_mta_sts(domain, provider)
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payload = json.dumps(asdict(result), sort_keys=True, separators=(",", ":"))
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if row is None:
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row = DNSCache(
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domain=domain,
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provider=provider_name,
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selectors_key=_CACHE_KEY,
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result_json=payload,
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checked_at=now,
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)
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db.add(row)
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else:
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row.result_json = payload
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row.checked_at = now
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try:
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db.commit()
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except IntegrityError:
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db.rollback()
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row = (
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db.query(DNSCache)
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.filter(
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DNSCache.domain == domain,
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DNSCache.provider == provider_name,
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DNSCache.selectors_key == _CACHE_KEY,
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)
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.first()
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)
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if row is None:
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raise
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row.result_json = payload
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row.checked_at = now
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db.commit()
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db.refresh(row)
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return result, False, row.checked_at
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