calibre is an e-book manager. Prior to 9.12.0, the calibre Content Server endpoint POST /book-update-annotations/{libraryid}/{bookid}/{fmt} in src/calibre/srv/books.py omits needsdbwrite=True, causing Router.dispatch() to skip ctx.checkforwriteaccess() before updateannotations() passes attacker-controlled JSON to db.mergeannotationsfor_book(), which allows a readonly user or an anonymous user on an unauthenticated deployment to persist unauthorized book annotation changes. This issue is fixed in version 9.12.0.