GeoServer is an open source server that allows users to share and edit geospatial data. It is possible to bypass the default REST API security and access the index page. The REST API security handles rest and its subpaths but not rest with an extension (e.g., rest.html). The REST API index can disclose whether certain extensions are installed. This vulnerability is fixed in 2.26.3 and 2.25.6. As a workaround, in ${GEOSERVER_DATA_DIR}/security/config.xml, change the paths for the rest filter to /rest.*,/rest/** and change the paths for the gwc filter to /gwc/rest.*,/gwc/rest/** and restart GeoServer.