EUVD-2026-69786
GHSA-r46q-wv4x-rj72
Severity by source
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Editor auth required (PR:L) and an admin must view the payload (UI:R); XSS executes in a different user's context so S:C, yielding high confidentiality/integrity of the admin session and no availability impact.
Primary rating from Vendor (vulncheck).
CVSS VectorVendor: vulncheck
Lifecycle Timeline
4DescriptionCVE.org
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.
AnalysisAI
Stored cross-site scripting in BookStack before 26.05.4 lets a user with editor-level permissions upload a malicious SVG through the drawing upload endpoint, which accepts unvalidated base64 content and stores it without inspection. The image gallery API later streams the file with no content-type validation and no CSP headers, so the embedded script executes in the browser of any administrator who views it - enabling admin session/account takeover. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Requires an authenticated account with editor permissions (drawing/image upload capability) - per CVSS PR:L this is not exploitable by fully unauthenticated users. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The input provides only a CVSS 4.0 vector (9.3, AV:N/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/SC:H/SI:H) - no EPSS, no CISA KEV entry, and no weaponized exploit. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Upgrade to BookStack 26.05.4 or later, which is the vendor-released patch (release https://github.com/BookStackApp/BookStack/releases/tag/v26.05.4, blog https://www.bookstackapp.com/blog/bookstack-release-v26-05-4/); the fix enforces an 'image/' Content-Type check in ImageService::streamImageFromStorageResponse() and rejects non-image files with HTTP 415 (commit ac0348a79f3ddd004ca87703948cb9c7d19a420a). … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours: Identify all BookStack deployments and current versions; immediately restrict editor-level permissions to trusted personnel and audit all SVG and drawing uploads for suspicious or unexpected content. …
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Same weakness CWE-79 – Cross-site Scripting (XSS)
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External POC / Exploit Code
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