A lot of OWASP CRS / ModSecurity users are postponing the CRS3 -> CRS4 migration since it's such an intimidating undertaking.
There is a new CRS plugin that brings sense and reason to the transition process.
The plugin allows you to keep up the security posture during the transition. You can run CRS4 in monitoring mode on top of a blocking CRS3 installation. That way you can weed out any new false positives and then slowly start to enable blocking CRS4 on individual URIs.
An additional option allows to run CRS4 on a configurable percentage of requests. A CRS4 sampling mode.
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