Migration on CRS Project

Migrating from CRS 3.3 to CRS 4.25 LTS — Part 3: The Plugin Architecture

Mon, 13 Apr 2026 09:00:00 -0300

This is Part 3 of the CRS 3.3 → 4.25 LTS migration series. Part 2 covered crs-setup.conf changes. This post covers the plugin architecture — the most structurally significant change in CRS 4, and the one that requires the most hands-on action from operators who used application exclusion packages in CRS 3.

The Key Change: Application Exclusions Are No Longer in Core

In CRS 3.3, the release tarball included a set of optional rule exclusion packages. If you ran WordPress, Nextcloud, phpBB, phpMyAdmin, Drupal, or a handful of other applications, you could include these files to suppress false positives specific to those applications:

Migrating from CRS 3.3 to CRS 4.25 LTS — Part 2: Configuration

Mon, 06 Apr 2026 09:00:00 -0300

This is Part 2 of the CRS 3.3 → 4.25 LTS migration series. Part 1 provided an overview of the migration. This post covers the crs-setup.conf changes — the most immediately breaking part of the upgrade for most operators.

If you take one thing from this post: do not reuse your CRS 3 crs-setup.conf with CRS 4 without reviewing every variable in it. Some variables were renamed, some were removed, and several new ones are required for features that did not exist in CRS 3.

Migrating from CRS 3.3 to CRS 4.25 LTS — Part 1: Overview

Mon, 30 Mar 2026 09:00:00 -0300

The release of CRS v4.25.0 LTS marks the moment the CRS 4 generation has its long-term support anchor. If you have been running CRS 3.3.x — waiting for stability before committing to an upgrade — that moment is now.

This is the first post in a series walking through everything you need to know to migrate from CRS 3.3.9 (the last CRS 3 LTS release) to CRS 4.25.0 LTS. The series is not a quick upgrade guide. It is a deliberate, post-by-post treatment of each dimension of the migration so that you can plan and execute without surprises.