Recently, several open source software tools such as CesiumJS and iTowns have been developed for dealing with 3-dimensional spatial data. These tools mainly focus on visualization of 3D spatial data based on WebGL. An open-sourced server capable of storing, sharing and querying 3D spatial data has not yet been developed. GeoServer, one of the representative open source spatial data servers, provides many powerful features. In particular, it supports connecting to and publishing spatial data from a variety of data sources. GeoServer also supports Web Feature Service (WFS), which is a standard protocol established by the Open Geospatial Consortium to request geospatial feature data. However, GeoServer provides functions only for two-dimensional geometry, so it provides few functions for handling 3D spatial data. Because JTS Topology Suite, which is an important component of GeoServer, does not support 3D spatial operations, it also does not support solid geometries. In this paper, we discuss extension modules of GeoServer that we have implemented to handle 3D spatial data. First, instead of JTS, our modules adopted a geometry model based on the ISO 19107 standard and support 3D spatial operations from the Simple Feature CGAL library. Based on this geometry model, we have implemented new internal data structures that represent spatial information from the Feature interface in GeoServer. Second, we also extended the DataStore module to handle and store 3D spatial information for several data sources such as GeoJSON, GML and PostGIS. Finally, we extended the WFS module to share 3D spatial data via GeoServer.