Executive brief
BookWyrm is a decentralized social reading platform that allows users to share and discuss books. The vulnerability allows authenticated users to favorite or unfavorite private statuses (followers-only and direct messages) they should not have access to, potentially exposing private content and triggering unwanted notifications to other users.
Technical details
BookWyrm through version 0.9.1 fails to validate user visibility permissions in the Favorite and Unfavorite view handlers (bookwyrm/views/interaction.py). The vulnerability exists because the views retrieve a Status object by ID without checking whether the authenticated user has permission to view or interact with it. An authenticated attacker can POST directly to the favorite endpoint with any status ID, creating unauthorized favorites on private statuses, triggering ActivityPub broadcasts, and enumerating private status IDs through response differentiation (different HTTP responses for accessible vs. inaccessible statuses). The vulnerability requires authentication but allows cross-user interaction with restricted content.
Affected products
- BookWyrm BookWyrm through 0.9.1
Timeline
- 2026-09-05: disclosed