Audiobookshelf is a self-hosted audiobook and podcast server. Starting in version 2.17.0 and prior to version 2.19.1, a flaw in the authentication bypass logic allows unauthenticated requests to match certain unanchored regex patterns in the URL. Attackers can craft URLs containing substrings like "/api/items/1/cover" in a query parameter (?r=/api/items/1/cover) to partially bypass authentication or trigger server crashes under certain routes. This could lead to information disclosure of otherwise protected data and, in some cases, a complete denial of service (server crash) if downstream code expects an authenticated user object. Version 2.19.1 contains a patch for the issue.
When trying to keep information confidential, an attacker can often infer some of the information by using statistics.