vacuum-wall/docs/security.md

Security Model

Privilege Model

Vacuum Wall uses two distinct system users bridged by a shared group (the WebUI user's primary group):

• vacuum-walld (daemon user): Runs the vacuum-walld background daemon, which is the only process with sudo access. The daemon communicates with the WebUI over a Unix socket at data/daemon.sock. All privileged operations — firewall rule changes, nginx reloads, dnsmasq config writes, WireGuard tunnel management — are executed by the daemon through a restricted sudo whitelist at /etc/sudoers.d/vacuum-walld.
• WebUI user (default: repo owner in --dev mode): Runs the Flask management WebUI. Has zero sudo access. If the WebUI process is compromised, an attacker cannot invoke sudo directly — they are confined to the sandboxed Flask process with no privilege escalation path.

ACME certificate operations via acme.sh run as the WebUI user — not as root, and not as the daemon user. The automated renewal timer (vacuum-wall-acme.timer) runs acme.sh --cron as {{ USER_NAME }}. When triggered from the WebUI or daemon, acme.sh also runs as the non-root process invoking it, using webroot validation that does not require binding to privileged ports.

This design follows the principle of least privilege: only the daemon process holds sudo access, and only for explicitly enumerated commands. The WebUI user is completely isolated from sudo.

Communication Between WebUI and Daemon

The WebUI communicates with the daemon via synchronous HTTP requests over a Unix socket (data/daemon.sock), owned by vacuum-walld:<group> with mode 0660. The shared group membership allows the WebUI user to connect to the socket. The daemon runs an aiohttp server that routes requests to handler modules (daemon/handlers/*.py), which execute the privileged commands.

Sudo Whitelist

The file /etc/sudoers.d/vacuum-walld grants the daemon user (vacuum-walld) passwordless sudo access to a strict set of commands. The WebUI user has no sudo access. Each daemon entry is scoped to a single binary with allowed arguments:

Category	Whitelisted Command	Purpose
Firewall	firewall-cmd *	All firewalld operations (zone management, rules, services, ports)
Nginx	nginx -s reload	Graceful nginx configuration reload
Nginx	nginx -t	Nginx configuration syntax validation
Nginx file ops	cp -- * /etc/nginx/, /etc/nginx/conf.d/, /etc/nginx/snippets/	Copy rendered config files to system paths
Nginx file ops	rm /etc/nginx/conf.d/vacuum-wall.conf, /etc/nginx/snippets/vacuum-wall-ssl.conf	Clean up generated nginx config files
Nginx file ops	chown root:root /etc/nginx/snippets/vacuum-wall-ssl.conf	Ensure correct ownership of SSL snippet
Dnsmasq	systemctl reload dnsmasq	Apply updated dnsmasq configuration
Dnsmasq	systemctl is-active dnsmasq	Check dnsmasq service status
Dnsmasq file ops	cp -- * /etc/dnsmasq.d/	Copy rendered config files
Dnsmasq file ops	tee /etc/dnsmasq.d/vacuum-wall.conf	Write dnsmasq configuration
Dnsmasq file ops	mkdir -p /etc/dnsmasq.d	Ensure target directory exists
Dnsmasq leases	cat /var/lib/dnsmasq/dnsmasq.leases	Read dnsmasq lease table
WireGuard	wg-quick *	WireGuard tunnel lifecycle (up, down, save, show)
WireGuard	wg *	WireGuard status and peer management
WireGuard file ops	cp -- * /etc/wireguard/	Copy rendered config files
WireGuard file ops	chown root:root /etc/wireguard/wg0.conf	Ensure correct ownership of WG config
Certificates	(none)	acme.sh runs as the non-root service user directly; no sudo escalation is needed (webroot validation is used)
Network queries	ip -o link show	List network interfaces
Network queries	ip -o addr show	List IP addresses on interfaces
Logs	journalctl --unit=* -n *	Query systemd journal for managed services
Logs	cat /var/log/nginx/*	Read nginx access and error logs

Key safety properties:

• Each Cmnd entry specifies the full path to the binary (e.g., /usr/bin/firewall-cmd).
• Wildcard entries exist only for commands where the full argument space is needed (firewall-cmd *, wg-quick *, wg *), but none grant shell access or arbitrary command execution.
• NOPASSWD is used so the application never prompts for a password. Defaults:<user> restricts the secure path and disables TTY requirement.
• The sudoers file is rendered from a Jinja2 template at install time, substituting the configured user name.

Web Security

Management Interface

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. The .htpasswd file is stored at data/nginx/.htpasswd.

The management interface does not set security hardening headers (e.g., X-Content-Type-Options, X-Frame-Options, HSTS). It relies on nginx basic authentication, SSL termination, and the systemd sandbox for its security boundary.

Proxy Domains

Every proxied domain configured in Vacuum Wall enforces:

• HTTP-to-HTTPS redirect — All HTTP requests return a 301 Permanent Redirect to the HTTPS equivalent.
• HTTP Strict Transport Security (HSTS) — The Strict-Transport-Security header is set with a long max-age and includeSubDomains to prevent downgrade attacks.
• Security headers on all proxied responses:
  • X-Content-Type-Options: nosniff — Prevents MIME-type sniffing.
  • X-Frame-Options: DENY — Prevents clickjacking via iframes.
  • X-XSS-Protection: 1; mode=block — Enables browser XSS filtering.
  • Referrer-Policy: strict-origin-when-cross-origin — Limits referrer information leakage.

Additional proxy headers (extra_headers in the domain config) are delivered to the upstream backend via nginx proxy_set_header directives — they are not sent as response headers to clients.

TLS Configuration

The default nginx SSL configuration enforces modern TLS only:

• Protocols: TLSv1.2 and TLSv1.3. Older protocols (SSLv3, TLSv1.0, TLSv1.1) are disabled.
• Cipher suites: A curated set of AEAD ciphers using ECDHE key exchange (ECDHE-ECDSA and ECDHE-RSA with AES-GCM and CHACHA20-POLY1305). No non-ECDHE ciphers are included.
• ssl_prefer_server_ciphers defaults to off (client chooses).
• Session settings: ssl_session_timeout 1d, ssl_session_cache shared:TLS:10m, ssl_session_tickets off.

Systemd Hardening

Both vacuum-wall.service (WebUI) and vacuum-walld.service (daemon) apply comprehensive systemd sandboxing directives to isolate their processes from the rest of the system:

Directive	Value	Effect
ProtectSystem	strict	Mounts the entire file system as read-only, except explicitly allowed paths
ReadWritePaths	project dir, /tmp, and (WebUI only) config/, data/ subdirs	The project directory and runtime paths are writable
PrivateTmp	yes	Provides a private /tmp and /var/tmp namespace
NoNewPrivileges	yes	Prevents the process from gaining new privileges via setuid/setgid
PrivateDevices	yes	Hides all device files under /dev
ProtectKernelTunables	yes	Makes /proc/sys, /sys, and /proc/sysrq-trigger read-only
ProtectKernelModules	yes	Disables init_module and finit_module syscalls
ProtectControlGroups	yes	Mounts /sys/fs/cgroup as read-only
ProtectHostname	yes	Prevents the process from changing the system hostname
RestrictNamespaces	yes	Prevents creating new namespaces
RestrictSUIDSGID	yes	Removes setuid/setgid bits from newly created files
LockPersonality	yes	Prevents changing the execution domain
MemoryDenyWriteExecute	yes	Prevents creating memory regions that are both writable and executable
SystemCallFilter	@system-service	Allows only a curated set of system calls safe for services
RestrictRealtime	yes	Prevents the process from acquiring realtime scheduling priorities
RestrictAddressFamilies	AF_UNIX AF_INET AF_INET6	Restricts available address families
IPAddressDeny	any	Drops all network traffic by default
IPAddressAllow	localhost	Allows only loopback communication (required to reach the other process at 127.0.0.1)

The WebUI unit additionally restricts address families and denies all IP traffic except to localhost — it cannot reach any external network interface. Both units use template variables ({{ USER_NAME }}, {{ USER_GROUP }}, {{ USER_DAEMON_NAME }}, {{ PROJECT_DIR }}) rendered at install time.

This hardening ensures that even if either process is compromised, the attacker is confined to a sandboxed environment with no direct network access, no write access outside the project directory, and no ability to escalate privileges through kernel interfaces.

Network Security

Default Deny

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.

Zone-Based Traffic Isolation

The lib/firewall module is a generic firewalld parser with no hardcoded zone definitions. Zone structure is defined declaratively in config/firewall/config.json at runtime. A typical deployment uses:

Zone	Interface	Purpose	Behavior
external	WAN (e.g., eth0)	Untrusted Internet-facing	Only essential services (HTTPS, WireGuard) are open. ICMP echo is rate-limited.
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.
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.
trusted / loopback	lo	Localhost communication	unrestricted; used for the Flask-to-nginx management proxy.
Custom zones	—	DMZ, guest networks, etc.	Additional zones can be created to isolate specific network segments with their own rule sets.

IP Forwarding and NAT

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.

Certificate Security

acme.sh Integration

Certificate management is handled by acme.sh, which stores all certificates and private keys under PROJECT_DIR/data/acme/ (set via the ACME_HOME environment variable). The directory is owned by and writable only by the service users.

Private Key Protection

Private key material is never exposed through the WebUI API. The API returns certificate metadata such as domain names, validity dates, file paths, and renewal status. File paths are returned so downstream tooling (nginx, cert management) can reference them. When a domain's certificate is needed by nginx, the rendered nginx configuration references the acme.sh file paths directly via ssl_certificate and ssl_certificate_key directives — no symlinks are created.

HSTS Enforcement

All HTTPS proxy domains (excluding the management interface) 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 proxied domains and their subdomains, preventing SSL stripping attacks.

Modern TLS Only

As noted in the Web Security section, the default SSL snippet enforces TLSv1.2 and TLSv1.3 with strong AEAD cipher suites using ECDHE key exchange. The cipher suite list excludes weak ciphers, EXPORT grades, RC4, DES, 3DES, MD5, and null ciphers.