Audiobookshelf is a self-hosted audiobook and podcast server. Prior to version 2.21.0, an improper input handling vulnerability in the /api/upload
endpoint allows an attacker to perform a reflected cross-site scripting (XSS) attack by submitting malicious payloads in the libraryId
field. The unsanitized input is reflected in the server’s error message, enabling arbitrary JavaScript execution in a victim's browser. This issue has been patched in version 2.21.0.