security-alert-center/backend/app/services/problem_rules.py

"""Problem rule evaluators (v1): brute-force, privilege spike, host silence."""

from __future__ import annotations

from dataclasses import dataclass
from datetime import datetime, timedelta, timezone

from sqlalchemy import func, select
from sqlalchemy.orm import Session

from app.config import get_settings
from app.models import Event, Host
from app.services.host_health import HEARTBEAT_TYPE, agent_status

BRUTE_FAILED_TYPES = frozenset({"ssh.login.failed", "rdp.login.failed"})
PRIVILEGE_SUDO_TYPE = "privilege.sudo.command"

RULE_BRUTE_FORCE = "rule:brute_force_burst"
RULE_PRIVILEGE_SPIKE = "rule:privilege_spike"
RULE_HOST_SILENCE = "rule:host_silence"


@dataclass(frozen=True)
class RuleMatch:
    rule_id: str
    correlation_type: str
    title: str
    summary: str
    severity: str
    fingerprint_suffix: str = ""


def _now() -> datetime:
    return datetime.now(timezone.utc)


def _event_source_ip(event: Event) -> str:
    details = event.details if isinstance(event.details, dict) else {}
    ip = details.get("source_ip") or details.get("ip")
    return str(ip) if ip else "unknown"


def count_events_in_window(
    db: Session,
    *,
    host_id: int,
    event_type: str,
    since: datetime,
    source_ip: str | None = None,
) -> int:
    rows = db.scalars(
        select(Event).where(
            Event.host_id == host_id,
            Event.type == event_type,
            Event.occurred_at >= since,
        )
    ).all()
    if source_ip is None:
        return len(rows)
    return sum(1 for e in rows if _event_source_ip(e) == source_ip)


def last_heartbeat_at(db: Session, host_id: int) -> datetime | None:
    return db.scalar(
        select(func.max(Event.received_at)).where(
            Event.host_id == host_id,
            Event.type == HEARTBEAT_TYPE,
        )
    )


def evaluate_brute_force_burst(db: Session, event: Event) -> RuleMatch | None:
    if event.type not in BRUTE_FAILED_TYPES:
        return None
    settings = get_settings()
    source_ip = _event_source_ip(event)
    since = _now() - timedelta(minutes=settings.sac_brute_force_window_minutes)
    count = count_events_in_window(
        db,
        host_id=event.host_id,
        event_type=event.type,
        since=since,
        source_ip=source_ip,
    )
    if count < settings.sac_brute_force_threshold:
        return None
    return RuleMatch(
        rule_id=RULE_BRUTE_FORCE,
        correlation_type=event.type,
        fingerprint_suffix=f"ip{source_ip}",
        title=f"Brute-force burst: {count} failed logins",
        summary=(
            f"{count} событий {event.type} за {settings.sac_brute_force_window_minutes} мин "
            f"(IP {source_ip}, порог {settings.sac_brute_force_threshold})"
        ),
        severity="high",
    )


def evaluate_privilege_spike(db: Session, event: Event) -> RuleMatch | None:
    if event.type != PRIVILEGE_SUDO_TYPE:
        return None
    settings = get_settings()
    since = _now() - timedelta(minutes=settings.sac_privilege_spike_window_minutes)
    count = count_events_in_window(
        db,
        host_id=event.host_id,
        event_type=event.type,
        since=since,
    )
    if count < settings.sac_privilege_spike_threshold:
        return None
    return RuleMatch(
        rule_id=RULE_PRIVILEGE_SPIKE,
        correlation_type=event.type,
        title=f"Privilege spike: {count} sudo commands",
        summary=(
            f"{count} событий {event.type} за {settings.sac_privilege_spike_window_minutes} мин "
            f"(порог {settings.sac_privilege_spike_threshold})"
        ),
        severity="warning" if count < settings.sac_privilege_spike_threshold * 2 else "high",
    )


def host_silence_match_for_host(
    db: Session,
    host_id: int,
    *,
    hostname: str | None = None,
    now: datetime | None = None,
) -> RuleMatch | None:
    """Сформировать RuleMatch host_silence, если последний heartbeat устарел."""
    settings = get_settings()
    ref = now or _now()
    hb = last_heartbeat_at(db, host_id)
    if hb is None:
        return None
    if agent_status(hb, stale_minutes=settings.sac_heartbeat_stale_minutes, now=ref) != "stale":
        return None
    if hostname is None:
        host = db.get(Host, host_id)
        hostname = host.hostname if host else f"host#{host_id}"
    hb_utc = hb.replace(tzinfo=timezone.utc) if hb.tzinfo is None else hb.astimezone(timezone.utc)
    age_min = int((ref - hb_utc).total_seconds() // 60)
    return RuleMatch(
        rule_id=RULE_HOST_SILENCE,
        correlation_type="host.silence",
        title=f"Host silence: {hostname}",
        summary=(
            f"Нет свежего agent.heartbeat более {settings.sac_heartbeat_stale_minutes} мин "
            f"(последний ~{age_min} мин назад)"
        ),
        severity="high",
    )


def evaluate_host_silence(db: Session, event: Event) -> RuleMatch | None:
    if event.type == HEARTBEAT_TYPE:
        return None
    host = db.get(Host, event.host_id)
    hostname = host.hostname if host else None
    return host_silence_match_for_host(db, event.host_id, hostname=hostname)


def evaluate_immediate_high(event: Event) -> RuleMatch | None:
    """Одиночные high/critical и известные типы (ban, mass bruteforce)."""
    problem_types = frozenset({"ssh.ip.banned", "ssh.bruteforce.mass"})
    if event.severity not in frozenset({"high", "critical"}) and event.type not in problem_types:
        return None
    rule_id = "high_severity" if event.severity in frozenset({"high", "critical"}) else f"type:{event.type}"
    return RuleMatch(
        rule_id=rule_id,
        correlation_type=event.type,
        title=event.title,
        summary=event.summary,
        severity=event.severity,
    )


def resolve_host_silence_problems(db: Session, host_id: int) -> int:
    """Закрыть open/ack host silence при свежем heartbeat."""
    from app.models import Problem

    problems = db.scalars(
        select(Problem).where(
            Problem.host_id == host_id,
            Problem.rule_id == RULE_HOST_SILENCE,
            Problem.status.in_(("open", "acknowledged")),
        )
    ).all()
    for problem in problems:
        problem.status = "resolved"
    if problems:
        db.flush()
    return len(problems)


def build_fingerprint(host_id: int, correlation_type: str, rule_id: str, suffix: str = "") -> str:
    base = f"h{host_id}"
    if suffix:
        base = f"{base}:{suffix}"
    return f"{base}:t{correlation_type}:r{rule_id}"


def pick_rule_match(db: Session, event: Event) -> RuleMatch | None:
    """Первое сработавшее правило (приоритет: burst → spike → silence → immediate)."""
    for evaluator in (
        evaluate_brute_force_burst,
        evaluate_privilege_spike,
        evaluate_host_silence,
    ):
        match = evaluator(db, event)
        if match is not None:
            return match
    return evaluate_immediate_high(event)