# Enodia Sentinel Specification

This document defines Enodia Sentinel as an IDS, IPS, and EDR system, not only a
signature IDS. The current implementation is a local Linux sensor with evidence
capture, integrity monitoring, anti-rootkit checks, a dashboard, alert delivery,
and dry-run prevention/response planning. The intended product is a defensive
control plane for a host or small fleet: detect compromise, prevent or contain
known-bad behavior through explicit operator workflows, prove what changed,
preserve useful evidence, guide response, and make sensor tampering visible.

## Product Definition

Enodia Sentinel is a zero-runtime-dependency Linux host security agent. It runs
as a local daemon, observes high-signal host behavior, records forensic context
when something suspicious happens, and exposes the result through local files,
JSON, a read-only dashboard, push notifications, and command-line tools.

The long-term product should combine six functions:

| Function | Purpose |
|---|---|
| Detection | Find active compromise behavior: reverse shells, fileless execution, new listeners, suspicious egress, persistence edits, and privilege-escalation artifacts. |
| Prevention | Recommend and, after explicit review, apply containment actions such as stopping malicious processes, blocking C2 peers, disabling persistence, or quarantining files. |
| Integrity | Prove whether important files, packages, baselines, and Sentinel's own footprint changed. |
| Evidence | Capture enough context for incident response without forcing the operator to reproduce a live state after the attacker is gone. |
| Response | Provide safe, explicit operator workflows for triage, containment, and recovery. |
| Assurance | Make the agent itself measurable: heartbeat, dead-man's switch, tamper-evidence, and future remote attestation. |

## Design Principles

1. **High-signal first.** Prefer detections that are cheap to observe and costly
   for attackers to avoid, even if that means a smaller rule set.
2. **Evidence over noise.** Every alert should carry enough context to answer
   "what happened, where, and what should I inspect next?"
3. **Zero dependency core.** The base daemon must run with the Python standard
   library only. Optional layers such as bcc/eBPF may degrade cleanly.
4. **One local trust boundary is not enough.** On-box checks are useful but
   root can tamper with them. Important anchors should move to signed package
   metadata, immutable filesystem controls, external watchers, or future
   remote attestation.
5. **Operator control.** Sentinel should recommend response actions before it
   takes them. Destructive containment must be opt-in and auditable.
6. **Bash prototype remains the oracle.** The original shell implementation and
   red-team harness preserve behavioral compatibility for core signatures.

## Current Scope: Local IDS/IPS/EDR

### Poll Detectors

The daemon builds one `SystemState` per sweep and runs pure detector functions
against cached process and socket data:

| Detector | Signal |
|---|---|
| `reverse_shell` | Interpreter with a network socket on fd 0/1/2. |
| `ld_preload` | Non-empty `/etc/ld.so.preload` or writable-path `LD_PRELOAD`. |
| `deleted_exe` | Process executing from a deleted file or `memfd:` image. |
| `input_snooper` | Non-allowlisted process holding keyboard/input/HID devices open. |
| `credential_access` | Non-allowlisted process reading credential databases, private keys, browser stores, or secret profiles. |
| `stealth_network` | Non-allowlisted raw, SCTP, DCCP, packet, MPTCP, TIPC, XDP, or vsock activity. |
| `memory_obfuscation` | Non-allowlisted executable anonymous/memfd/deleted mappings, RWX memory, or mapped process-hiding libraries. |
| `new_listener` | Listening socket absent from the startup baseline. |
| `new_suid` | New SUID/SGID binary, critical in writable locations. |
| `persistence` | Changes to cron, systemd units, SSH keys, shell rc files, and similar persistence locations. |
| `egress` | Interpreter with an established connection to a public IP. |

### Event Detection

Optional bcc eBPF monitors feed event rule engines. The `execve` stream closes
the polling gap for short-lived commands and supports custom TOML rules without
code changes. The syscall stream watches short-lived memory and anti-analysis
behavior: RWX `mprotect`/`mmap`, `memfd_create`, sensitive `ptrace`, seccomp,
cross-process memory access, and memory locking. Failure is fail-safe: if a
probe cannot load, polling continues.

### Integrity and Tamper-Evidence

Sentinel includes several integrity layers:

| Layer | Current behavior |
|---|---|
| FIM baseline | SHA-256 baseline for critical files and Sentinel's own footprint. |
| Package verification | Optional `pacman -Qkk` verification for package-owned files. |
| Package DB anchor | Detects out-of-band edits to `/var/lib/pacman/local`. |
| Signed-package anchor | Compares on-disk files to `.MTREE` hashes from cached signed packages. |
| Heartbeat | Writes daemon liveness for local dashboard and external watchdog use. |
| Rootcheck | Cross-view checks for hidden processes, processes hidden from `ps`, hidden modules, hidden TCP/UDP/raw/special-protocol sockets, promiscuous interfaces, known rootkit modules, raw ICMP/SCTP-style channels, and kernel/module taint. |

### Evidence Capture

When a fresh alert survives cooldown, Sentinel writes:

- A human-readable snapshot.
- A JSON snapshot suitable for automation and SIEM import.
- Relevant process tree, sockets, environment hints, file descriptors, and
  response guidance.
- Event log entries and dashboard-visible status.

### Operator Interfaces

| Interface | Role |
|---|---|
| CLI | Run daemon, one-shot checks, baseline management, FIM checks, package DB checks, rootcheck, posture audit, incident review/export, triage, status/watchdog, and response planning. |
| Logs | Durable local evidence under `/var/log/enodia-sentinel`. |
| Dashboard | HTTPS-only read-only web view for status, incidents, timelines, alert browsing, posture findings, event tail, and response-plan previews. |
| Push | ntfy, Pushover, and generic webhook notifications. |
| Red-team harness | Safe drills for testing signatures and demos. |

CLI-generated response plans are durable artifacts: `respond plan` writes the
reviewed dry-run plan under `response-plans/` and appends a JSONL
`response-audit.log` record. Dashboard/API previews remain read-only and do not
create artifacts.

Current IPS scope is explicit prevention workflow, not transparent inline
enforcement. Sentinel can recommend evidence preservation, process
freeze/termination, outbound IP blocks, systemd unit disablement, suspicious-file
quarantine, package-owner lookup, and follow-up verification. It does not
execute those commands until a future audited `--apply` workflow is designed,
tested, and documented.

## Target Scope: Host Security Platform

The next product shape should make Enodia useful before, during, and after an
incident.

### Prevent

- Configuration posture checks for risky SSH, sudo, systemd, cron, kernel,
  package manager, firewall, and service settings.
- Baseline drift reports for newly exposed services, new SUID files, new
  autostarts, new users/groups, and sensitive permission changes.
- A policy mode that can fail CI or package build checks for unsafe host images.

### Detect

- More event sources: `tcp_connect`, `bind`, `accept`, file-write events for
  persistence paths, module loading, privilege transitions, and LSM hooks.
- Correlation across signals: "web service spawned shell" + "new listener" +
  "persistence write" should become one incident, not three unrelated alerts.
- Optional YARA-style and Sigma-like local rules if they can stay dependency
  light and operator-readable.

### Investigate

- Incident timeline files derived from event log, snapshots, FIM diffs,
  package transactions, process lineage, and network observations.
- Stable incident IDs that group related alerts over time.
- `enodia-sentinel incident show <id>` and `incident export <id>` workflows.

### Respond

- Safe containment actions behind explicit flags:
  stop a process, disable a systemd unit, remove a persistence entry, block an
  IP with nftables, quarantine a file, or freeze evidence.
- Dry-run by default, with JSON plans that can be reviewed before execution.
- Response playbooks that are code-reviewed data files, not shell snippets
  pasted into documentation.

### Recover

- Package restore guidance: identify owning package, verify cache signature,
  reinstall package, and re-run integrity checks.
- Baseline reconciliation workflow after confirmed legitimate changes.
- Post-incident report generation from captured evidence.

### Assure

- External anchor storage for baselines and package DB fingerprints.
- Signed snapshots or hash-chained event logs.
- Remote watchdog improvements and eventually fleet controller support.
- Optional TPM/IMA integration for machines that can support measured boot.

## Data Model

The current `Alert` object is the public detection unit:

| Field | Meaning |
|---|---|
| `sid` | Stable signature ID for tuning, documentation, and downstream rules. |
| `severity` | `MEDIUM`, `HIGH`, or `CRITICAL`. |
| `signature` | Stable machine-readable detection name. |
| `classtype` | Snort/Suricata-style category. |
| `key` | Cooldown and deduplication identity. |
| `detail` | Human-readable explanation. |
| `pids` | Process IDs for snapshot deep dives. |

Incident grouping adds an `incident_id` at the snapshot-report level (not inside
each `Alert`), so it groups one or more alerts without changing the alert JSON
schema. Grouping is process-lineage first, with a time-window fallback for
PID-less alerts; see the [command reference](COMMAND_REFERENCE.md) and
[roadmap](ROADMAP.md).

## Configuration Model

Configuration is a TOML file loaded at startup. Unknown keys are ignored so
newer config templates remain tolerable on older agents, but documentation
should clearly mark version-specific fields. Existing defaults should prefer
detection correctness over suppression. Convenience suppression knobs should
remain explicit and reviewable.

## Security Model

Sentinel runs as root because it must inspect root-owned files, process state,
file descriptors, and sockets. The systemd unit should continue to keep the
root process narrow: read-mostly, constrained writable paths, no new privileges,
restricted namespaces, and only the capabilities needed for the enabled layers.

Local root can eventually defeat any purely local sensor. Sentinel's answer is
layering: signed package metadata, immutable files, off-box watchdogs, external
anchors, and future kernel/attestation features.

## Non-Goals

- Replacing a full enterprise SIEM.
- Silent self-hiding or rootkit-like persistence.
- Automatic destructive remediation without explicit operator approval.
- Shipping a broad dependency tree in the default agent.
- Claiming complete protection against a custom kernel implant.

## Acceptance Criteria For New Platform Features

A feature is ready when it has:

- A stable `sid`/signature or documented command contract.
- Unit tests for pure logic and a safe integration path where practical.
- JSON output or a durable artifact suitable for automation.
- Configuration documented in the sample TOML and README or relevant docs.
- Failure behavior that does not take down the daemon.
- Clear operator guidance for false positives, limitations, and response.