ElasticSearch introduced some restrictions on the use of plugins from versions above 7.11
In fact it seems that the configsync plugin is no longer usable due to the new restrictions.
Fess requires the installation of the plugin which to be visible must be defined its path in elasticsearch.yml; for example :
configsync.config_path: D: / Elastic / Elasticsearch / config /
But installation of this plugin fails with this error :
Exception in thread “main” java.lang.IllegalArgumentException: plugin policy [C:\Program Files\Elastic\Elasticsearch\7.12.1\plugins.installing-14280001803523461252\plugin-security.policy] contains illegal permission (“java.io.FilePermission” “<>” “read,write”) in global grant
contains the report of a problem similar to mine and the response of an ElasticSearch technician.