The CU Filter allows designers to create either system or user palettes. Any user connected to a geodatabase can view its system palettes, but only the user who creates a user palette can view that palette. You can use permissions to prevent non-admin users from creating system palettes.
User palettes are stored in the MM_CU_SEARCH_XML table, with system palettes kept in the MM_CU_SYS_PALETTES_XML table in the geodatabase. A user must have create and edit permissions on this table to create or edit system palettes. If you want to prevent a user from creating or editing system palettes, remove the user's create and edit permissions on MM_CU_SYS_PALETTES_XML.