# 05 — Security

## Summary

Security on this deployment is layered: Cloudflare at the edge, UFW at
the node, k3s RBAC + Pod Security at the orchestrator, TLS between
long-haul components, and dedicated service accounts with dropped
capabilities inside containers. This chapter documents each layer, the
rationale, and what's currently missing (and why).

## Threat model

Who we're defending against, in rough order of likelihood:

1. **Opportunistic scanners** — bots scanning random IPv4 ranges for
   known vulnerabilities. Mitigated by the firewall.
2. **Credential stuffing / brute-force** — especially against SSH and
   admin login. Mitigated by key-only SSH, strong passwords, rate limits.
3. **Compromised external service** — if Neon, Backblaze, or Cloudflare
   were breached, attacker would have access to whatever we store there.
   Mitigated by scoped credentials, least-privilege API keys.
4. **Compromised container image** — if Gitea or our build pipeline
   were compromised, malicious code could reach prod. Mitigated by
   (a) Gitea is behind authentication, (b) image pull secrets scoped,
   (c) containers run non-root with minimal capabilities.
5. **Insider threat** — not really a threat for a solo operator.
6. **State actor** — not in threat model. At our scale this is
   effectively unaddressable without becoming a security company.

Explicitly **not** in threat model:
- DDoS at a scale that saturates Cloudflare. We pay $0 for CF; their
  DDoS mitigation is included but not unlimited. If we got hit with a
  large attack, we'd move to a paid plan.
- Physical access to Hetzner datacenters. That's their problem.

## Layer 1 — Cloudflare edge

Cloudflare sits in front of every public request.

### What Cloudflare does for us

| Protection | How it works |
|---|---|
| TLS termination | CF presents a cert for `*.myhoneydue.com`; clients encrypt to CF |
| DDoS mitigation | Automatic on all plans including Free |
| Bot filtering | "Under Attack" mode + bot score based blocking |
| IP concealment | Origin IPs not in DNS; attackers can't directly scan |
| WAF rules | CF Free includes managed ruleset for common exploits |
| Rate limiting | Free tier: 10k requests/10min; more on paid plans |

### What Cloudflare does **not** do

- **Authenticate users** — that's the app's job
- **Authorize requests** — that's the app's job
- **Protect origin if origin IP leaks** — once someone knows a node IP
  they can bypass CF. Mitigation: keep origin firewall strict (Chapter 4).
- **Encrypt between CF and origin** — we're on SSL=Flexible, so CF↔origin
  is HTTP. This is in our TODO (Chapter 20, upgrade to Full-strict).

### The proxy-IP problem

Cloudflare publishes its IP ranges
([cloudflare.com/ips](https://www.cloudflare.com/ips/)). Any client can
verify a request came from a CF IP by checking the remote address. Our
Traefik is configured to trust `X-Forwarded-Proto` (so the Go API sees
`https` even though origin received HTTP) only from CF IP ranges:

```yaml
# deploy-k3s/manifests/traefik-helmchartconfig.yaml
additionalArguments:
  - "--entrypoints.web.forwardedHeaders.trustedIPs=173.245.48.0/20,..."
```

This means a malicious request that bypasses CF (by hitting the node IP
directly) can't spoof headers — Traefik ignores `X-Forwarded-*` unless
the source IP is in CF's ranges.

**TODO** (Chapter 20): Enforce at UFW level — allow 80/tcp only from
CF IP ranges. Today any IP can reach the origin on port 80.

## Layer 2 — Node (OS, SSH, firewall)

Each node runs Ubuntu 24.04.3 LTS with:

### SSH hardening

`/etc/ssh/sshd_config` on each node:

```
Port 22
PermitRootLogin no
PasswordAuthentication no
PubkeyAuthentication yes
AllowUsers deploy
```

Result:
- Only the `deploy` user can log in
- Only with a public key (no password)
- Root cannot log in remotely

The public key authorized for `deploy`:

```
ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIBU9xTTBD78tYUqHijgyU9PDqtmS4NuM/6uy8XgDzva+ hetzner2@myhoneydue.com
```

(Note: the comment field says "hetzner2" but it's the key for all three
nodes — the comment is the key's identifier, not a restriction.)

Private key is at `~/.ssh/hetzner` on the operator workstation.

### Sudo

The `deploy` user has unrestricted sudo with no password
(`/etc/sudoers.d/deploy`):

```
deploy ALL=(ALL) NOPASSWD: ALL
```

This is convenient but broad. A compromise of the `deploy` SSH key =
root on the node. Mitigations:
- Key is stored only on the operator workstation, not checked into git
- Operator workstation has disk encryption (macOS FileVault)
- Operator workstation has a passphrase for the key (ssh-agent cache)

Future hardening: scope sudo to specific commands that deploy workflows
need (e.g., `/usr/sbin/ufw`, `/usr/bin/systemctl`), but this requires
enumerating every command we might run, which breaks ad-hoc debugging.

### fail2ban

**Not installed.** fail2ban would ban IPs that fail SSH auth repeatedly.
Because we disable password auth entirely, the attack surface is tiny (an
attacker with the private key wins; failed-public-key attempts are
functionally DDoS, not credential-stuffing). Installing fail2ban is on
the TODO list anyway because it buys us rate-limiting on SSH bot noise.

### unattended-upgrades

**Not installed.** Security patches require manual `apt upgrade`. This is
a gap. Install and configure for security-only updates as soon as time
permits.

### UFW firewall

See [Chapter 4](./04-firewall.md) for the complete ruleset. Summary:
default-deny incoming, specific allows for SSH (22), HTTP (80), HTTPS
(443), k3s API from operator IP (6443), and inter-node cluster ports.

## Layer 3 — Kubernetes RBAC

K3s inherits full Kubernetes RBAC. Every component that talks to the API
server has a ServiceAccount with only the permissions it needs.

### System accounts

K3s creates these by default:
- `kube-system:admin` — cluster admin, used by `kubectl`
- `kube-system:coredns` — for CoreDNS
- `kube-system:traefik` — for Traefik ingress controller
- `kube-system:helm-install-traefik` — for the Helm chart installer

We don't touch these.

### Application service accounts

Our `rbac.yaml` creates four ServiceAccounts in the `honeydue` namespace:

```yaml
apiVersion: v1
kind: ServiceAccount
metadata:
  name: api
  namespace: honeydue
automountServiceAccountToken: false   # ← important
```

Same for `admin`, `worker`, `redis`.

**`automountServiceAccountToken: false`** means pods don't get a k8s
API token mounted in `/var/run/secrets/kubernetes.io/serviceaccount/`.
Without it, a compromised pod cannot query the Kubernetes API even if
the default service account has broad permissions.

### What the app pods CAN'T do

Our app service accounts have **no RoleBindings or ClusterRoleBindings**.
They cannot:
- List, get, create, update, delete any Kubernetes resource
- Read other namespaces' secrets
- Schedule workloads
- View cluster state

If the api container were fully compromised (RCE), the attacker would
have:
- Network access to other pods in the `honeydue` namespace (Chapter 16)
- Read access to our ConfigMap + Secrets (mounted into the container)
- No ability to pivot to other parts of the cluster via the k8s API

## Layer 4 — Pod Security

Every pod runs with restrictive security context:

```yaml
securityContext:
  runAsNonRoot: true
  runAsUser: 1000        # api; different per service
  runAsGroup: 1000
  fsGroup: 1000
  seccompProfile:
    type: RuntimeDefault

containers:
  - securityContext:
      allowPrivilegeEscalation: false
      readOnlyRootFilesystem: true
      capabilities:
        drop: ["ALL"]
```

### What each setting does

| Setting | Effect |
|---|---|
| `runAsNonRoot: true` | Pod refuses to start if the image's default user is root |
| `runAsUser: 1000` | Override to UID 1000 (app user) |
| `allowPrivilegeEscalation: false` | Process cannot become root via setuid, ptrace, etc. |
| `readOnlyRootFilesystem: true` | `/` is read-only; writes require explicit volumes |
| `capabilities: drop: [ALL]` | No Linux capabilities (NET_ADMIN, SYS_TIME, etc.) |
| `seccompProfile: RuntimeDefault` | Restrict syscalls to containerd's default seccomp allowlist |

Read-only root means our app images must declare writable volumes for
anything mutable:

```yaml
volumeMounts:
  - name: tmp
    mountPath: /tmp
volumes:
  - name: tmp
    emptyDir:
      sizeLimit: 64Mi
```

If the app needs to write somewhere else (e.g., Next.js cache), we mount
an emptyDir there explicitly.

### Traefik exception

Traefik needs `CAP_NET_BIND_SERVICE` to bind ports 80/443 on the host
network. Its security context adds just that one capability back:

```yaml
securityContext:
  capabilities:
    drop: [ALL]
    add: [NET_BIND_SERVICE]
  readOnlyRootFilesystem: true
  runAsGroup: 65532
  runAsNonRoot: true
  runAsUser: 65532
```

The `net.ipv4.ip_unprivileged_port_start=0` sysctl on the nodes
complements this — on older kernels NET_BIND_SERVICE alone isn't enough
in the host netns.

### Pod Security Admission (PSA)

Kubernetes has a built-in admission controller for enforcing Pod Security
Standards at the namespace level:

```yaml
apiVersion: v1
kind: Namespace
metadata:
  name: honeydue
  labels:
    pod-security.kubernetes.io/enforce: restricted
    pod-security.kubernetes.io/enforce-version: latest
```

We **don't currently set this**. We get the equivalent effect from
the explicit securityContext on each pod, but namespace-level enforcement
would catch new workloads that forget to set it. **TODO** (Chapter 20).

## Layer 5 — Network Policies

The `deploy-k3s/manifests/network-policies.yaml` scaffold defines:

- **default-deny-all** — deny all ingress and egress by default in the
  `honeydue` namespace
- **allow-dns** — allow egress UDP/TCP 53 to CoreDNS
- **allow-ingress-to-api** — allow Traefik (`kube-system` namespace) to
  reach api pods on port 8000
- **allow-ingress-to-admin** — same, for admin:3000

**These are not currently applied.** Without them, our pods can freely
talk to anything — including, theoretically, malicious destinations if
an attacker gets RCE inside a pod.

**TODO** (Chapter 20): Apply network policies. The scaffold is there; we
just need to `kubectl apply -f deploy-k3s/manifests/network-policies.yaml`
and test that nothing breaks.

### What network policies would prevent

| Attack scenario | NetworkPolicy blocks |
|---|---|
| Pod A compromised, attacker SSHs sideways to pod B | Yes (explicit allow needed) |
| Pod RCE → scan internal networks | Yes (default deny egress) |
| Pod RCE → exfil to attacker's C2 | Yes (outbound to internet needs egress rule) |

Without policies, all of these work.

## TLS and encryption

### CF ↔ user

Always TLS 1.2+ (CF doesn't support older). CF presents an automatically-
renewed Let's Encrypt or CF-managed cert for `*.myhoneydue.com`.

### CF ↔ origin

**Plaintext HTTP** (SSL = Flexible). An attacker with access to the
Cloudflare-to-Hetzner path could read traffic. In practice nobody who
isn't Cloudflare or Hetzner sits on that path.

**TODO** (Chapter 20): Upgrade to SSL = Full (strict) with a Cloudflare
Origin CA certificate. This encrypts CF ↔ origin and verifies that
origin's cert is the CF-issued one (prevents MitM if DNS is compromised).

### API ↔ Neon Postgres

**TLS 1.3** via `DB_SSLMODE=require`. The Go app's postgres driver (pgx)
negotiates TLS and verifies Neon's cert against the system CA bundle.
Connection fails if TLS can't be established.

### API ↔ Backblaze B2

**HTTPS** (B2 doesn't support HTTP). `B2_USE_SSL=true` in our ConfigMap
(though actually the app reads `STORAGE_USE_SSL` — see Chapter 9 for this
vestigial variable's story).

### Worker ↔ Fastmail SMTP

**STARTTLS** on port 587. The Go `wneessen/go-mail` library uses
`TLSOpportunistic` mode — which means it connects plain then upgrades via
STARTTLS. Fastmail always supports STARTTLS, so in practice every
connection is encrypted.

### API/worker ↔ Redis

**Plaintext** inside the cluster. Redis 7 supports TLS (redis-tls.conf,
`redis-server --tls-port`), but we haven't enabled it because Redis is
on the overlay network, not exposed externally, and only holds cache +
queue state.

### Pod-to-pod (Flannel overlay)

**Plaintext VXLAN** over Hetzner's public network. See
[Chapter 3 §Layer 3](./03-networking.md#layer-3--pod-overlay-flannel-vxlan).
TODO to switch to WireGuard backend.

## Secrets management

### Kubernetes Secrets

Our k8s Secrets are stored in etcd. etcd-at-rest encryption is **not
currently enabled** — a compromise of the etcd data directory would
expose Secret values. Given:
- Nodes have disk encryption at the Hetzner hypervisor layer
- Attacker needs root on the node to read etcd
- Our operator access is already root-via-sudo

This is an accepted risk. **TODO** (Chapter 20): enable encryption at rest
for etcd. K3s supports it via `--secrets-encryption` flag on the server.

### What Secrets we have

```
$ kubectl get secrets -n honeydue
NAME                TYPE                             DATA   AGE
gitea-credentials   kubernetes.io/dockerconfigjson   1      ...
honeydue-apns-key   Opaque                           1      ...
honeydue-secrets    Opaque                           9      ...
```

Contents:

| Secret | Key | Source |
|---|---|---|
| `gitea-credentials` | `.dockerconfigjson` | PAT for Gitea registry (image pulls) |
| `honeydue-apns-key` | `apns_auth_key.p8` | Placeholder p8 file (push off) |
| `honeydue-secrets` | `POSTGRES_PASSWORD` | Neon DB password |
| `honeydue-secrets` | `SECRET_KEY` | 64-char random, app signing key |
| `honeydue-secrets` | `EMAIL_HOST_PASSWORD` | Fastmail app password |
| `honeydue-secrets` | `FCM_SERVER_KEY` | "disabled-no-push-accounts-yet" placeholder |
| `honeydue-secrets` | `REDIS_PASSWORD` | Empty (no auth on internal Redis) |
| `honeydue-secrets` | `B2_KEY_ID` | B2 app key ID |
| `honeydue-secrets` | `B2_APP_KEY` | B2 app key secret |
| `honeydue-secrets` | `ADMIN_EMAIL` | `admin@myhoneydue.com` |
| `honeydue-secrets` | `ADMIN_PASSWORD` | Generated 24-char initial admin password |

### Source of truth

The Secret values came from:
- `deploy/secrets/*.txt` files on the operator workstation (gitignored)
- `deploy/prod.env` (gitignored)
- `deploy/registry.env` (gitignored)

These Swarm-era files are still the canonical source. If you need to
recreate Secrets in a new cluster:

```bash
cd honeyDueAPI-go
kubectl create secret generic honeydue-secrets -n honeydue \
  --from-literal=POSTGRES_PASSWORD="$(cat deploy/secrets/postgres_password.txt)" \
  --from-literal=SECRET_KEY="$(cat deploy/secrets/secret_key.txt)" \
  --from-literal=EMAIL_HOST_PASSWORD="$(cat deploy/secrets/email_host_password.txt)" \
  ...
```

The full recreation script is in Chapter 17 (Runbook).

### Secret rotation

Not automated. To rotate (e.g., after a compromise):

1. Generate new value: `openssl rand -base64 32`
2. Update the secret:
   ```bash
   kubectl create secret generic honeydue-secrets -n honeydue \
     --from-literal=SECRET_KEY='new-value' \
     --dry-run=client -o yaml | kubectl apply -f -
   ```
3. Restart dependent pods:
   ```bash
   kubectl rollout restart -n honeydue deploy/api deploy/worker
   ```
4. Update `deploy/secrets/secret_key.txt` to match
5. Revoke the old credential at the source (Neon, Fastmail, etc.)

## Container image provenance

Images come from `gitea.treytartt.com/admin/*`. We have **no image
signing or verification** (cosign/sigstore) in place. A compromise of
the Gitea registry = the ability to push malicious images that would be
pulled into prod on the next rollout.

Mitigations:
- Gitea itself is behind login; PAT is scoped to read:packages +
  write:packages only
- Gitea runs on the operator's infrastructure (same operator account)
- Image tags are SHA-pinned (`:237c6b8`) not `:latest` → attacker can't
  replace an existing tag's image without us noticing the digest change

**TODO** (Chapter 20): Add cosign signing at build time, verify at pull
time.

## Operator workstation security

The operator workstation has:
- macOS with FileVault (full disk encryption)
- Login password required
- Private keys in `~/.ssh/` (mode 0600)
- Kubeconfig at `~/.kube/honeydue-k3s.yaml` (mode 0600) — contains a bearer
  token to the cluster

**Losing the laptop would require immediate credential rotation:**
- New SSH key, redeploy public part on all 3 nodes
- New kubeconfig: run `sudo cat /etc/rancher/k3s/k3s.yaml` on hetzner1,
  copy to workstation, update `KUBECONFIG` env
- Rotate operator-access PATs on Gitea, Neon, Cloudflare, Backblaze

## Compliance notes

This stack is **not currently certified** for:
- HIPAA — we transit and store health-related data but haven't contractually
  bound any BAA
- SOC 2 — no auditing, no documented controls beyond this document
- PCI-DSS — we don't handle card data; Apple/Google IAP handles payments
- GDPR — we follow GDPR best practices (data minimization, user deletion)
  but haven't had a formal assessment

If honeyDue ever needs any of these, the infrastructure is compatible
but the operational processes around it would need formal work.

## Operator cheat sheet

```bash
# See all RBAC-related resources in a namespace
kubectl get sa,role,rolebinding -n honeydue

# Check what a ServiceAccount can do
kubectl auth can-i --list --as=system:serviceaccount:honeydue:api -n honeydue

# Verify pod is running with expected security context
kubectl get pod <pod> -n honeydue -o jsonpath='{.spec.securityContext}'
kubectl get pod <pod> -n honeydue -o jsonpath='{.spec.containers[0].securityContext}'

# List all Secrets (without revealing content)
kubectl get secret -n honeydue
kubectl describe secret honeydue-secrets -n honeydue  # shows keys, not values

# Decode a secret (CAREFUL: prints plaintext)
kubectl get secret honeydue-secrets -n honeydue -o jsonpath='{.data.SECRET_KEY}' | base64 -d
```

## References

- [Kubernetes Pod Security Standards][psa]
- [Kubernetes RBAC][rbac]
- [Kubernetes NetworkPolicy][netpol]
- [Cloudflare IP ranges][cf-ips]
- [K3s secrets encryption][k3s-secrets]
- [SSH hardening guide][ssh-guide]

[psa]: https://kubernetes.io/docs/concepts/security/pod-security-standards/
[rbac]: https://kubernetes.io/docs/reference/access-authn-authz/rbac/
[netpol]: https://kubernetes.io/docs/concepts/services-networking/network-policies/
[cf-ips]: https://www.cloudflare.com/ips/
[k3s-secrets]: https://docs.k3s.io/security/secrets-encryption
[ssh-guide]: https://linux-audit.com/audit-and-harden-your-ssh-configuration/
