https://coreruleset.org/20260406/migrating-crs-3-to-4-part-2-configuration/
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Migrating from CRS 3.3 to CRS 4.25 LTS — Part 2: Configuration
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.






