Installing the RAT module
To install the Raster Attribute Table support:
- From the website download page, locate your release, and download: http://sourceforge.net/projects/geoserver/files/GeoServer/2025.1/extensions/geoserver-2025.1-rat-plugin.zip - Warning - Make sure to match the version of the extension to the version of GeoServer. 
- Extract these files and place the JARs in - WEB-INF/lib.
- Perform any configuration required by your servlet container, and then restart.