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.
The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.