Hardening nftables for a Default-Deny Posture

A truly sovereign network perimeter does not rely on third-party applications to manage traffic; it relies on the kernel. For users of Linux-based systems like Peppermint OS, nftables is the modern successor to iptables, offering a more efficient and readable way to define the rules of your network. To achieve a “Default-Deny” posture, your system must be configured to drop every single packet by default, only allowing traffic that specifically matches your secure encrypted tunnel.

Building the Lockdown Script

The goal of hardening your firewall is to prevent “leaks” at the most fundamental level. If your VPN or SSH tunnel fails, the firewall acts as a physical barrier that the data cannot bypass. This is the ultimate expression of the “Kill-Switch” philosophy, implemented directly in the network stack.

Core Components of a Sovereign Firewall

• Table and Chain Definition: Establish a “filter” table with input, output, and forward chains set to a default policy of drop. This ensures the machine is silent unless a specific rule permits speech.
• Interface Binding: Create rules that specifically allow traffic on the loopback interface (for local system processes) and your tunnel interface (e.g., wg0). All other physical interfaces (eth0, wlan0) should be restricted to tunnel-negotiation traffic only.
• Stateful Inspection: Utilize “connection tracking” to allow established and related traffic to return, ensuring that once you initiate a secure connection, the response can reach you without opening a permanent hole in your perimeter.

The Minimalist Advantage

By moving your firewall logic into nftables, you remove the need for GUI-based “UFW” or “Firewalld” wrappers. This reduces system bloat and ensures that your security rules are loaded early in the boot process, long before any user-space applications or browsers can initiate a connection.

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