Executive brief
BookStack is a document management and wiki-like platform. The vulnerability allows authenticated users with basic image-management permissions to modify or delete other users' profile pictures (avatars) by exploiting insufficient access controls in the API. An attacker could replace or delete any user's avatar without needing administrative privileges, potentially impacting account identity and user trust.
Technical details
This is a broken access control vulnerability (CWE-284) in BookStack's Image Gallery API endpoints. The flaw stems from missing content-type validation and insufficient authorization checks when handling image operations. An authenticated attacker with image-update or image-delete permissions can supply a user avatar's ID to the API controller; the system loads the image without gallery and drawio restrictions that are enforced by the web controller. When the avatar's uploaded_to field matches a page ID accessible to the attacker, the authorization check incorrectly passes, allowing rename, replace, or delete operations on target avatars without requiring user-management permission. The vulnerability requires API authentication but can be exploited by lower-privileged users. BookStack 26.05.4 addresses this with enhanced MIME-based content-type validation.
Affected products
- BookStack BookStack before 26.05.4
Timeline
- 2026-08-24: disclosed
- 2026-08-24: patched: Fixed in BookStack v26.05.4 with additional MIME-based content type checks