CVE-2026-67204: Bookstackapp Bookstack

Medium severity, CVSS 5.4. EPSS: 0.4% chance of exploitation in the next 30 days.

BookStack before 26.05.4 contains a broken access control vulnerability that allows authenticated API users with image-update or image-delete permissions to manipulate other users' avatars by exploiting missing content-type restrictions in the Image Gallery API endpoints. Attackers can supply a user avatar's ID to the API controller, which loads any image type without the web controller's gallery and drawio restrictions, and when the avatar's uploaded_to field matches a page ID accessible to the attacker, the authorization check passes allowing the attacker to rename, replace, or delete the target user's avatar without requiring user-management permission.

Affected products

Published 2026-08-24. Last modified 2026-09-24.