Initial commit: SSL proxy / firewall appliance
Flask WebUI behind nginx reverse proxy with zone-based firewall, DHCP, WireGuard, and ACME certificate management.
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# Security Model
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## Privilege Model
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The Vacuum Wall management WebUI (Flask application) runs as the unprivileged `vacuum-wall` system user. The application never runs as root. All privileged operations — firewall rule changes, nginx reloads, TLS certificate issuance — are executed through a restricted sudo whitelist defined at `/etc/sudoers.d/vacuum-wall`.
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This design follows the principle of least privilege: only explicitly enumerated commands are permitted to escalate. There is no path to a full root shell from the application or the `vacuum-wall` user. If the WebUI process is compromised, an attacker is confined to the sudo whitelist surface rather than gaining unrestricted system access.
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## Sudo Whitelist
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The file `/etc/sudoers.d/vacuum-wall` grants the `vacuum-wall` user passwordless sudo access to a strict set of commands. Each entry is scoped to a single binary with allowed arguments. The categories are:
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| Category | Whitelisted Command | Purpose |
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|---|---|---|
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| Firewall | `firewall-cmd *` | All firewalld operations (zone management, rules, services, ports) |
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| Nginx | `nginx -s reload` | Graceful nginx configuration reload |
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| Nginx | `nginx -t` | Nginx configuration syntax validation |
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| Dnsmasq | `systemctl reload dnsmasq` | Apply updated dnsmasq configuration |
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| Dnsmasq | `systemctl is-active dnsmasq` | Check dnsmasq service status |
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| WireGuard | `wg-quick *` | WireGuard tunnel lifecycle (up, down, save, show) |
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| WireGuard | `wg *` | WireGuard status and peer management |
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| Certificates | `acme.sh` (via `bash -c`) | Let's Encrypt certificate issuance and renewal |
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| File writes | `sudo cp` to `/etc/nginx/`, `/etc/dnsmasq.d/`, `/etc/wireguard/` | Copy rendered config files to system paths |
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| Logs | `sudo journalctl --unit=*` | Query systemd journal for managed services |
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| Logs | `sudo cat /var/log/nginx/*` | Read nginx access and error logs |
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| File writes | `sudo tee` | Write configuration data to protected paths |
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Key safety properties:
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- Each `Cmnd` entry specifies the full path to the binary (e.g., `/usr/bin/firewall-cmd`).
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- No wildcard entries grant shell access or arbitrary command execution.
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- The `acme.sh` entry is restricted to certificate operations through an explicit `bash -c` wrapper that only passes acme-related arguments.
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- `DEFAULT!/usr/bin/sudo` and `NOPASSWD` are used so the application never prompts for a password and cannot chain sudo calls.
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## Web Security
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### Management Interface
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The Flask WebUI binds exclusively to `127.0.0.1:9090`. It is not exposed directly to any network interface. All external access to the management UI is routed through an nginx reverse proxy on the designated management domain, which provides SSL termination and HTTP Basic Authentication using an `.htpasswd` file.
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### Proxy Domains
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Every proxied domain configured in Vacuum Wall enforces:
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- **HTTP-to-HTTPS redirect** — All HTTP requests return a 301 Permanent Redirect to the HTTPS equivalent.
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- **HTTP Strict Transport Security (HSTS)** — The `Strict-Transport-Security` header is set with a long max-age to prevent downgrade attacks.
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- **Security headers** on all proxied responses:
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- `X-Content-Type-Options: nosniff` — Prevents MIME-type sniffing.
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- `X-Frame-Options: DENY` — Prevents clickjacking via iframes.
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- `X-XSS-Protection: 1; mode=block` — Enables browser XSS filtering.
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- `Referrer-Policy: strict-origin-when-cross-origin` — Limits referrer information leakage.
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- `Content-Security-Policy` rules can be customized per-domain via the configuration.
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### TLS Configuration
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The default nginx SSL configuration enforces modern TLS only:
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- **Protocols**: TLSv1.2 and TLSv1.3. Older protocols (SSLv3, TLSv1.0, TLSv1.1) are disabled.
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- **Cipher suites**: A curated set of AEAD ciphers (ECDHE-ECDSA and ECDHE-RSA key exchange with AES-GCM and CHACHA20-POLY1305).
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- **DH parameters**: 2048-bit generated Diffie-Hellman parameters are used when ECDHE is not selected.
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- **OCSP stapling** is enabled for faster certificate validation.
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- **ssl_prefer_server_ciphers** can be toggled per-domain; the default is to let the client choose.
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## Systemd Hardening
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The `vacuum-wall.service` unit file applies a comprehensive set of systemd sandboxing directives to isolate the WebUI process from the rest of the system:
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| Directive | Value | Effect |
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| `ProtectSystem` | `strict` | Mounts the entire file system as read-only, except explicitly allowed paths |
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| `ProtectHome` | `read-only` | Makes `/home`, `/root`, and `/run/user` inaccessible |
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| `ReadWritePaths` | `/home/wall/vacuum-wall/data /tmp` | Only the application data directory and `/tmp` are writable |
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| `PrivateTmp` | `yes` | Provides a private `/tmp` and `/var/tmp` namespace |
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| `NoNewPrivileges` | `yes` | Prevents the process from gaining new privileges via `setuid`/`setgid` |
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| `IPAddressDeny` | `all` | Drops all network traffic |
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| `IPAddressAllow` | `localhost` | Allows only loopback communication (required to reach nginx upstream at 127.0.0.1:9090) |
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| `PrivateDevices` | `yes` | Hides all device files under `/dev` |
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| `ProtectKernelTunables` | `yes` | Makes `/proc/sys`, `/sys`, and `/proc/sysrq-trigger` read-only |
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| `ProtectKernelModules` | `yes` | Disables `init_module` and `finit_module` syscalls |
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| `ProtectControlGroups` | `yes` | Mounts `/sys/fs/cgroup` as read-only |
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| `ProtectHostname` | `yes` | Prevents the process from changing the system hostname |
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| `RestrictNamespaces` | `yes` | Prevents creating new namespaces |
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| `RestrictSUIDSGID` | `yes` | Removes setuid/setgid bits from newly created files |
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| `LockPersonality` | `yes` | Prevents changing the execution domain |
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| `MemoryDenyWriteExecute` | `yes` | Prevents creating memory regions that are both writable and executable |
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| `SystemCallFilter` | `@system-service` | Allows only a curated set of system calls safe for services |
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This hardening ensures that even if the Flask application is compromised, the attacker is confined to a sandboxed environment with no direct network access, no write access outside the data directory, and no ability to escalate privileges through kernel interfaces.
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## Network Security
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### Default Deny
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The firewalld default zone policy is set to deny all incoming traffic. Only explicitly allowed services and ports are accessible. Outbound traffic is permitted by default.
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### Zone-Based Traffic Isolation
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| Zone | Interface | Purpose | Behavior |
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| `external` | WAN (e.g., `eth0`) | Untrusted Internet-facing | Only essential services (HTTPS, WireGuard) are open. ICMP echo is rate-limited. |
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| `internal` | LAN (e.g., `eth1`) | Trusted local network | DHCP and DNS served to clients. Masquerade (NAT) enabled for outbound Internet access. All outbound traffic from the LAN is allowed. |
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| `vpn` | WireGuard (`wg0`) | WireGuard tunnel traffic | Semi-trusted. Firewall rules control which internal services VPN peers can reach. Traffic to the LAN is restricted to specific services and ports. |
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| `trusted` / `loopback` | `lo` | Localhost communication | unrestricted; used for the Flask-to-nginx management proxy. |
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| Custom zones | — | DMZ, guest networks, etc. | Additional zones can be created to isolate specific network segments with their own rule sets. |
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### IP Forwarding and NAT
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IP forwarding (`net.ipv4.ip_forward = 1`) is enabled system-wide to allow routing between zones (LAN to Internet, VPN to LAN). However, actual traffic flow is controlled by firewalld rules. Masquerade is enabled on the `internal` zone so that LAN clients get NAT translation when accessing the Internet through the Vacuum Wall router.
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## Certificate Security
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### acme.sh Integration
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Certificate management is handled by acme.sh, which stores all certificates and private keys in the `vacuum-wall` user's home directory under `~/.acme.sh/`. The directory is owned by and writable only by the `vacuum-wall` user.
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### Private Key Protection
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Private keys are never exposed through the WebUI API or returned in API responses. The API only returns certificate metadata such as domain names, validity dates, and renewal status. When a domain's certificate is needed by nginx, the rendered nginx configuration references the file paths managed by acme.sh (`~/.acme.sh/<domain>/fullchain.cer` and `~/.acme.sh/<domain>/<domain>.key`), and nginx reads them directly through symbolic links or includes.
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### HSTS Enforcement
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All HTTPS proxy domains have HTTP Strict Transport Security enabled at the nginx layer with a long max-age and the `includeSubDomains` directive. This ensures browsers always use HTTPS for the domain and all subdomains, preventing SSL stripping attacks.
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### Modern TLS Only
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As noted in the Web Security section, the default ssl snippet enforces TLSv1.2 and TLSv1.3 with strong AEAD cipher suites. Weak ciphers, EXPORT grades, RC4, DES, 3DES, MD5, and null ciphers are explicitly excluded.
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