vacuum-wall/docs/security.md

Security Model

Privilege Model

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.

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.

Sudo Whitelist

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:

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
Dnsmasq	systemctl reload dnsmasq	Apply updated dnsmasq configuration
Dnsmasq	systemctl is-active dnsmasq	Check dnsmasq service status
WireGuard	wg-quick *	WireGuard tunnel lifecycle (up, down, save, show)
WireGuard	wg *	WireGuard status and peer management
Certificates	acme.sh (via bash -c)	Let's Encrypt certificate issuance and renewal
File writes	sudo cp to /etc/nginx/, /etc/dnsmasq.d/, /etc/wireguard/	Copy rendered config files to system paths
Logs	sudo journalctl --unit=*	Query systemd journal for managed services
Logs	sudo cat /var/log/nginx/*	Read nginx access and error logs
File writes	sudo tee	Write configuration data to protected paths

Key safety properties:

• Each Cmnd entry specifies the full path to the binary (e.g., /usr/bin/firewall-cmd).
• No wildcard entries grant shell access or arbitrary command execution.
• The acme.sh entry is restricted to certificate operations through an explicit bash -c wrapper that only passes acme-related arguments.
• DEFAULT!/usr/bin/sudo and NOPASSWD are used so the application never prompts for a password and cannot chain sudo calls.

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 using an .htpasswd file.

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 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.
  • Content-Security-Policy rules can be customized per-domain via the configuration.

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 (ECDHE-ECDSA and ECDHE-RSA key exchange with AES-GCM and CHACHA20-POLY1305).
• DH parameters: 2048-bit generated Diffie-Hellman parameters are used when ECDHE is not selected.
• OCSP stapling is enabled for faster certificate validation.
• ssl_prefer_server_ciphers can be toggled per-domain; the default is to let the client choose.

Systemd Hardening

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:

Directive	Value	Effect
ProtectSystem	strict	Mounts the entire file system as read-only, except explicitly allowed paths
ProtectHome	read-only	Makes /home, /root, and /run/user inaccessible
ReadWritePaths	/home/wall/vacuum-wall/data /tmp	Only the application data directory and /tmp are writable
PrivateTmp	yes	Provides a private /tmp and /var/tmp namespace
NoNewPrivileges	yes	Prevents the process from gaining new privileges via setuid/setgid
IPAddressDeny	all	Drops all network traffic
IPAddressAllow	localhost	Allows only loopback communication (required to reach nginx upstream at 127.0.0.1:9090)
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

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.

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

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 in the vacuum-wall user's home directory under ~/.acme.sh/. The directory is owned by and writable only by the vacuum-wall user.

Private Key Protection

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.

HSTS Enforcement

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.

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. Weak ciphers, EXPORT grades, RC4, DES, 3DES, MD5, and null ciphers are explicitly excluded.