Kavita is a cross platform reading server. Prior to 0.9.0, the download, size-check, and chapter metadata endpoints do not enforce library-level authorization. A low-privileged user who knows or guesses a chapterId, volumeId, or seriesId belonging to a library they are not assigned to can download the full file contents, query file sizes, and read metadata for that content. This affects /api/Download/volume-size, /api/Download/chapter-size, /api/Download/series-size, /api/Download/volume, /api/Download/chapter, /api/Download/series, and /api/Chapter. This vulnerability is fixed in 0.9.0.