Larvitz Blog
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Welcome to Larvitz Blog! I’m Christian, a Senior Consultant by day and FreeBSD enthusiast by night, with over 20 years in enterprise IT. Here I write about FreeBSD jails, PF firewalling, self-hosting, Linux system administration, and anything that’s cleanly engineered. Most articles are hands-on guides born from running my own infrastructure, from dual-stack networking and Ansible automation to hosting a Mastodon instance on FreeBSD.

Have a question or want to discuss something? Find me on the Fediverse at @Larvitz@burningboard.net. I’m always happy to chat!

#security Articles

My Ansible Plugin Had a Jail Escape: CVE-2026-55074

For almost a year, my jailexec connection plugin let a compromised FreeBSD jail redirect a root-owned write onto the jail host. The input validation was fine. The problem was on which side of the jail boundary the paths were resolved. This is the story of the bug, the fix in 2.0.0, and the CVE that came with it.

FreeBSD Foundationals: The Boot Process - From the Loader to Boot Environments

The third in the FreeBSD Foundationals series. This one covers how FreeBSD actually boots: the stages from power-on to login, BIOS vs UEFI, the loader and loader.conf, the difference between read-only tunables and runtime sysctls, the modern way to load kernel modules with kld_list, managing it all safely with sysrc, a practical security-hardening baseline, and - the headline act - boot environments with bectl, the undo button that turns a broken upgrade into a thirty-second reboot.

mdo on FreeBSD 15: Base-System Privilege Delegation with mac_do

FreeBSD 15 ships mdo(1) and the mac_do(4) policy module in the base system. It replaces sudo and doas for most of my hosts, needs no ports, and configures with a single sysctl. This article walks through enabling it, the rule syntax, a few real examples, and a short detour into the security sysctls I run on every box.

Fedora Hummingbird: Distroless, Container-Native Linux and a Slim mastogreet

Fedora Hummingbird brings the distroless container model to a full, image-based rolling operating system, and it ships a catalog of hardened language images alongside it. I rebuild the mastogreet bot’s Containerfile on top of registry.access.redhat.com/hi/python to see what changes, what shrinks, and where the commercial Red Hat Hardened Images downstream fits in.

PF Firewall on FreeBSD: A Practical Guide

A comprehensive guide to configuring PF on FreeBSD, covering core concepts, practical configurations for jails and dual-stack networking, and advanced techniques including brute-force protection and bastion host setups with authpf.