fail2ban-ui/docs/security.md

Security guidance

This project can perform security-sensitive operations (bans, configuration changes). Deploy it as you would deploy every other administrative interface.

Recommended deployment posture

• Do not expose the UI directly to the Internet.
• Prefer one of:
  • VPN-only access
  • Reverse proxy with strict allowlists
  • OIDC enabled (in addition to network controls)

If you must publish it, put it behind TLS and an authentication layer, and restrict source IPs.

See docs/reverse-proxy.md for hardened proxy examples and WebSocket forwarding requirements.

Input validation

All user-supplied IP addresses are validated using Go's net.ParseIP and net.ParseCIDR before they are passed to any integration, command, or database query. This applies to:

• Ban/Unban callbacks (/api/ban, /api/unban)
• Manual ban/unban actions from the dashboard
• Advanced action test endpoint (/api/advanced-actions/test)
• All integration connectors (MikroTik, pfSense, OPNsense)

Integration-specific identifiers (address list names, alias names) are validated against a strict alphanumeric pattern ([a-zA-Z0-9._-]) to prevent injection in both SSH commands and API payloads.

WebSocket security

The WebSocket endpoint (/api/ws) is protected by:

• Origin validation: The upgrade handshake verifies that the Origin header matches the request's Host header (same-origin policy). Cross-origin WebSocket connections are rejected. This prevents cross-site WebSocket hijacking attacks.
• Authentication: When OIDC is enabled, the WebSocket endpoint requires a valid session.

Callback endpoint protection

The callback endpoints (/api/ban, /api/unban) are protected by CALLBACK_SECRET (X-Callback-Secret header). If no secret is specified, Fail2Ban UI generates one on first start. Additional hardening:

• Use a long, random secret and rotate it on suspected leakage
• Restrict network access so only known Fail2Ban hosts can reach callback endpoints

Rotate the secret if you suspect leakage.

SSH connector hardening

For SSH-managed hosts:

• Use a dedicated service account (not a human user).
• Require key-based auth.
• Restrict sudo to the minimum set of commands required to operate Fail2Ban (at minimum fail2ban-client * and systemctl restart fail2ban).
• Use filesystem ACLs for /etc/fail2ban rather than broad permissions to allow full modification capabilities for the specific user.

Integration connector hardening

When using external firewall integrations (MikroTik, pfSense, OPNsense):

• Use a dedicated service account on the firewall device with the minimum permissions needed (address-list management only on MikroTik; alias management only on pfSense/OPNsense).
• For pfSense/OPNsense: use a dedicated API token with limited scope.
• Restrict network access so the Fail2ban-UI host is the only source allowed to reach the firewall management interface.

Least privilege and file access

Local connector deployments typically require access to:

• /var/run/fail2ban/fail2ban.sock
• /etc/fail2ban/
• selected log paths (read-only, mounted to same place inside the container, where they are on the host.)

Avoid running with more privileges than necessary. If you run in a container, use the repository deployment guide and SELinux policies.

SELinux

If SELinux is enabled, use the policies provided in:

• deployment/container/SELinux/

Do not disable SELinux as a shortcut. Fix always labeling and policy issues instead. -> Everytime you read "to disable SELinux" you can close that guide :)

Alert provider security

Fail2Ban UI supports three alert providers: Email (SMTP), Webhook, and Elasticsearch. Each has specific security considerations.

Email (SMTP)

• Use TLS (Use TLS enabled) for all SMTP connections.
• Avoid disabling TLS verification (Skip TLS Verification) in production. If you must, ensure the network path to the SMTP server is trusted.
• Use application-specific passwords or OAuth tokens where supported (e.g. Gmail, Office365) instead of primary account passwords.

Webhook

• Use HTTPS endpoints whenever possible.
• If the webhook endpoint requires authentication, use custom headers (e.g. Authorization: Bearer <token>) rather than embedding credentials in the URL.
• Avoid disabling TLS verification for production endpoints. The Skip TLS Verification option exists for development/self-signed environments only.

Elasticsearch

• Use API key authentication over basic auth when possible. API keys can be scoped to specific indices and rotated independently.
• Restrict the API key to write-only access on the fail2ban-events-* index pattern. Avoid cluster-wide or admin-level keys.
• Consider using Elasticsearch's built-in role-based access control to limit what the Fail2Ban UI service account can do.

Audit and operational practices

• Back up /config (DB + settings) regularly.
• Treat the database as sensitive operational data.
• Keep the host and container runtime patched.
• Review Fail2Ban actions deployed to managed hosts as part of change control.