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.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.26%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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.
- CVSS 4.0
- 9.3 CRITICALCVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M
- EPSS
- 0.26% probability · 17th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-79
- Source
- disclosure@vulncheck.com
References
- https://github.com/BookStackApp/BookStack
- https://github.com/BookStackApp/BookStack/blob/v26.05.3/app/Uploads/ImageService.php
- https://github.com/BookStackApp/BookStack/commit/ac0348a79f3ddd004ca87703948cb9c7d19a420a
- 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
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.