The Note Mark backend has an unauthenticated API endpoint GET /api/books/{bookID}/notes that accepts a 'deleted=true' query parameter. When used on public books, this parameter bypasses the soft-delete filter, allowing unauthenticated users to access metadata of soft-deleted (trashed) notes. The exposed metadata includes note ID, title, slug, and timestamps, but not the note content. The root cause is improper authorization logic failing to limit soft-deleted note visibility to the note owner. A code fix involves restricting soft-deleted note listings to the book owner only, preventing public access to trashed notes.

This vulnerability leads to unauthorized disclosure of metadata for soft-deleted notes in public books to unauthenticated users. Although the note content is not exposed, sensitive metadata such as note identifiers and timestamps may reveal information the note owner intended to keep hidden. There is no impact on data integrity or availability. The CVSS 3.1 base score is 5.3 (medium severity), reflecting low impact on confidentiality and no impact on integrity or availability.

A patch is available that restricts access to soft-deleted notes exclusively to the book owner, preventing unauthenticated users from retrieving metadata of trashed notes in public books. Users of the affected Note Mark backend should apply the official fix to enforce proper authorization on the 'deleted=true' query parameter. No additional mitigation is indicated by the vendor advisory.