Hardening Network

A while back I hardened this Debian VM by hand — patched it, cut the attack surface, put a default-deny host firewall in front of it, sandboxed the custom services. I audited my own box and fixed the drift I found. The problem with auditing your own box is that you grade your own homework. You check the things you already think to check. So this time I handed the job to something that has no idea what I meant to do and only reports what’s actually there: Lynis, the system-auditing tool from CISOfy. It ran 274 tests and gave the VM a hardening index of 68 / 100. ...

A flat network trusts every device on it equally. A smart plug, a guest’s phone, and the machine holding my important data all share one space — so if any one of them is compromised, the attacker can reach the rest. Network segmentation breaks that flat space into separate zones and controls what may cross between them, shrinking the blast radius of any single compromise. I wanted to build that properly — VLANs and a firewall — on VMware Workstation with pfSense CE, and design three zones at deliberately different trust levels: ...

My Debian automation VM already sits behind a pfSense firewall with egress containment — it can reach the internet but not my home network. So why harden the VM itself? Because “behind a firewall” is doing less work than it sounds. Two paths reach into the VM without ever crossing pfSense, and an honest audit of my own box turned up drift I didn’t expect. This is the write-up: what the audit found, what I changed, and the systemd sandbox mistake that quietly broke a service. ...

This is a small home network — one router, a handful of devices. The point wasn’t complexity; it was applying the same discipline you would to a small office or lab environment. Treated that way, it doubles as practical study for Network+ and Security+. The router is an Arcadyan HWG2025 — the NBN-issued unit, Wi-Fi 7 with MLO, around 500 Mb down. An ISP router doesn’t give you much room to move, but it gives you enough to do this properly. ...