XSS in Bookstackapp Bookstack
CVE-2026-84695
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.
Vulnerability class: XSS (Cross-Site Scripting)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 8.7 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N.
EPSS exploit prediction
EPSS: 0.005 (39.2th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 39th percentile — 39.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.005 · change: +0.002
Affected products
Weakness classification (CWE)
References
- github.com/BookStackApp/BookStack (product)
- github.com/BookStackApp/BookStack/blob/v26.05.3/app/Uploads/ImageService.php (technical-description)
- github.com/BookStackApp/BookStack/commit/ac0348a79f3ddd004ca87703948cb9c7d19a42… (patch)
- github.com/BookStackApp/BookStack/releases/tag/v26.05.4 (release-notes)
- www.bookstackapp.com/blog/bookstack-release-v26-05-4/ (vendor-advisory)
- www.vulncheck.com/advisories/bookstack-before-26.05.4-stored-xss-via-drawing-up… (third-party-advisory)
Frequently asked questions
- What is CVE-2026-84695?
- CVE-2026-84695 is a high-severity vulnerability in Bookstackapp Bookstack, classified under Cross-site Scripting. CVSS score: 8.7/10. Published 2026-09-02.
- How severe is CVE-2026-84695?
- High severity. CVSS v3 base score is 8.7 out of 10.