docs: add security hardening plan

Based on security review findings, covering SSH hardening, firewall
enablement, log transport TLS, security alerting, and secrets management.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/plans/security-hardening.md

@@ -0,0 +1,224 @@
+# Security Hardening Plan
+
+## Overview
+
+Address security gaps identified in infrastructure review. Focus areas: SSH hardening, network security, logging improvements, and secrets management.
+
+## Current State
+
+- SSH allows password auth and unrestricted root login (`system/sshd.nix`)
+- Firewall disabled on all hosts (`networking.firewall.enable = false`)
+- Promtail ships logs over HTTP to Loki
+- Loki has no authentication (`auth_enabled = false`)
+- AppRole secret-IDs never expire (`secret_id_ttl = 0`)
+- Vault TLS verification disabled by default (`skipTlsVerify = true`)
+- Audit logging exists (`common/ssh-audit.nix`) but not applied globally
+- Alert rules focus on availability, no security event detection
+
+## Priority Matrix
+
+| Issue | Severity | Effort | Priority |
+|-------|----------|--------|----------|
+| SSH password auth | High | Low | **P1** |
+| Firewall disabled | High | Medium | **P1** |
+| Promtail HTTP (no TLS) | High | Medium | **P2** |
+| No security alerting | Medium | Low | **P2** |
+| Audit logging not global | Low | Low | **P2** |
+| Loki no auth | Medium | Medium | **P3** |
+| Secret-ID TTL | Medium | Medium | **P3** |
+| Vault skipTlsVerify | Medium | Low | **P3** |
+
+## Phase 1: Quick Wins (P1)
+
+### 1.1 SSH Hardening
+
+Edit `system/sshd.nix`:
+
+```nix
+services.openssh = {
+  enable = true;
+  settings = {
+    PermitRootLogin = "prohibit-password";  # Key-only root login
+    PasswordAuthentication = false;
+    KbdInteractiveAuthentication = false;
+  };
+};
+```
+
+**Prerequisite:** Verify all hosts have SSH keys deployed for root.
+
+### 1.2 Enable Firewall
+
+Create `system/firewall.nix` with default deny policy:
+
+```nix
+{ ... }: {
+  networking.firewall.enable = true;
+
+  # Use openssh's built-in firewall integration
+  services.openssh.openFirewall = true;
+}
+```
+
+**Useful firewall options:**
+
+| Option | Description |
+|--------|-------------|
+| `networking.firewall.trustedInterfaces` | Accept all traffic from these interfaces (e.g., `[ "lo" ]`) |
+| `networking.firewall.interfaces.<name>.allowedTCPPorts` | Per-interface port rules |
+| `networking.firewall.extraInputRules` | Custom nftables rules (for complex filtering) |
+
+**Network range restrictions:** Consider restricting SSH to the infrastructure subnet (`10.69.13.0/24`) using `extraInputRules` for defense in depth. However, this adds complexity and may not be necessary given the trusted network model.
+
+#### Per-Interface Rules (http-proxy WireGuard)
+
+The `http-proxy` host has a WireGuard interface (`wg0`) that may need different rules than the LAN interface. Use `networking.firewall.interfaces` to apply per-interface policies:
+
+```nix
+# Example: http-proxy with different rules per interface
+networking.firewall = {
+  enable = true;
+
+  # Default: only SSH (via openFirewall)
+  allowedTCPPorts = [ ];
+
+  # LAN interface: allow HTTP/HTTPS
+  interfaces.ens18 = {
+    allowedTCPPorts = [ 80 443 ];
+  };
+
+  # WireGuard interface: restrict to specific services or trust fully
+  interfaces.wg0 = {
+    allowedTCPPorts = [ 80 443 ];
+    # Or use trustedInterfaces = [ "wg0" ] if fully trusted
+  };
+};
+```
+
+**TODO:** Investigate current WireGuard usage on http-proxy to determine appropriate rules.
+
+Then per-host, open required ports:
+
+| Host | Additional Ports |
+|------|------------------|
+| ns1/ns2 | 53 (TCP/UDP) |
+| vault01 | 8200 |
+| monitoring01 | 3100, 9090, 3000, 9093 |
+| http-proxy | 80, 443 |
+| nats1 | 4222 |
+| ha1 | 1883, 8123 |
+| jelly01 | 8096 |
+| nix-cache01 | 5000 |
+
+## Phase 2: Logging & Detection (P2)
+
+### 2.1 Enable TLS for Promtail → Loki
+
+Update `system/monitoring/logs.nix`:
+
+```nix
+clients = [{
+  url = "https://monitoring01.home.2rjus.net:3100/loki/api/v1/push";
+  tls_config = {
+    ca_file = "/etc/ssl/certs/homelab-root-ca.pem";
+  };
+}];
+```
+
+Requires:
+- Configure Loki with TLS certificate (use internal ACME)
+- Ensure all hosts trust root CA (already done via `system/pki/root-ca.nix`)
+
+### 2.2 Security Alert Rules
+
+Add to `services/monitoring/rules.yml`:
+
+```yaml
+- name: security_rules
+  rules:
+    - alert: ssh_auth_failures
+      expr: increase(node_logind_sessions_total[5m]) > 20
+      for: 0m
+      labels:
+        severity: warning
+      annotations:
+        summary: "Unusual login activity on {{ $labels.instance }}"
+
+    - alert: vault_secret_fetch_failure
+      expr: increase(vault_secret_failures[5m]) > 5
+      for: 0m
+      labels:
+        severity: warning
+      annotations:
+        summary: "Vault secret fetch failures on {{ $labels.instance }}"
+```
+
+Also add Loki-based alerts for:
+- Failed SSH attempts: `{job="systemd-journal"} |= "Failed password"`
+- sudo usage: `{job="systemd-journal"} |= "sudo"`
+
+### 2.3 Global Audit Logging
+
+Add `./common/ssh-audit.nix` import to `system/default.nix`:
+
+```nix
+imports = [
+  # ... existing imports
+  ../common/ssh-audit.nix
+];
+```
+
+## Phase 3: Defense in Depth (P3)
+
+### 3.1 Loki Authentication
+
+Options:
+1. **Basic auth via reverse proxy** - Put Loki behind Caddy with auth
+2. **Loki multi-tenancy** - Enable `auth_enabled = true` and use tenant IDs
+3. **Network isolation** - Bind Loki only to localhost, expose via authenticated proxy
+
+Recommendation: Option 1 (reverse proxy) is simplest for homelab.
+
+### 3.2 AppRole Secret Rotation
+
+Update `terraform/vault/approle.tf`:
+
+```hcl
+secret_id_ttl  = 2592000  # 30 days
+```
+
+Add documentation for manual rotation procedure or implement automated rotation via the existing `restartTrigger` mechanism in `vault-secrets.nix`.
+
+### 3.3 Enable Vault TLS Verification
+
+Change default in `system/vault-secrets.nix`:
+
+```nix
+skipTlsVerify = mkOption {
+  type = types.bool;
+  default = false;  # Changed from true
+};
+```
+
+**Prerequisite:** Verify all hosts trust the internal CA that signed the Vault certificate.
+
+## Implementation Order
+
+1. **Test on test-tier first** - Deploy phases 1-2 to testvm01/02/03
+2. **Validate SSH access** - Ensure key-based login works before disabling passwords
+3. **Document firewall ports** - Create reference of ports per host before enabling
+4. **Phase prod rollout** - Deploy to prod hosts one at a time, verify each
+
+## Open Questions
+
+- [ ] Do all hosts have SSH keys configured for root access?
+- [ ] Should firewall rules be per-host or use a central definition with roles?
+- [ ] Should Loki authentication use the existing Kanidm setup?
+
+**Resolved:** Password-based SSH access for recovery is not required - most hosts have console access through Proxmox or physical access, which provides an out-of-band recovery path if SSH keys fail.
+
+## Notes
+
+- Firewall changes are the highest risk - test thoroughly on test-tier
+- SSH hardening must not lock out access - verify keys first
+- Consider creating a "break glass" procedure for emergency access if keys fail