Kavita is a cross platform reading server. Prior to 0.9.0, the ReaderController.GetImage endpoint is decorated with [AllowAnonymous], allowing completely unauthenticated access to page images from any chapter in any library. While the endpoint accepts an apiKey parameter, it is never validated. Since entity IDs are sequential integers, an unauthenticated attacker can trivially enumerate all content on the server. This vulnerability is fixed in 0.9.0.