CVE-2026-84695
HighCVSS 8.7Exploitation Probability (EPSS)
Low risk17th percentile - higher than 17% of all known CVEs
Summary
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.
Risk Assessment
The risk includes execution of malicious scripts in the administrator context, which can lead to session theft, account takeover, or further system compromise.
Recommendation
It is recommended to upgrade BookStack to version 26.05.4 or later, which includes a fix for SVG upload validation.
Other vulnerabilities in BookStack
See all- CVE-2026-89022High
BookStack before 26.05.5 contains an authentication bypass vulnerability in its social login implementation that allows unauthenticated attackers to sign in as arbitrary users by authenticating through a different social provider sharing the same driver_id namespace. Attackers can authenticate at one enabled social provider using a user ID that matches an account linked to a different social provider, bypassing credential verification entirely because the SocialAuthService::handleLoginCallback query ignores the driver column when retrieving linked account records.
- CVE-2026-86285Medium
A vulnerability was detected in BookStack up to 26.05.2. Affected by this issue is the function AttachmentController::getUpdateForm of the file app/Uploads/Controllers/AttachmentController.php of the component Attachment Edit Endpoint. The manipulation of the argument ID results in improper access controls. The attack may be launched remotely. The exploit is now public and may be used. The patch is identified as 4e406c41c4c8060a5795e74c66fb96362e54f400.
- CVE-2026-82450High
BookStack before version 26.05.4 contains a remote code execution vulnerability in the portable ZIP import functionality that allows users with Import Content and Create Books permissions to upload a PHP polyglot file as a book cover. Attackers can bypass image extension validation by embedding a PHP file with a .php filename in the ZIP archive, which is stored in the public web root and executed by unauthenticated requests.
- CVE-2026-67204Medium
Broken access control vulnerability in BookStack before 26.05.4 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.
- CVE-2026-5484Medium
A weakness has been identified in BookStackApp BookStack up to version 26.03 in the chapterToMarkdown function of app/Exports/ExportFormatter.php (Chapter Export Handler). Manipulating the pages argument can lead to improper access controls. The attack can be launched remotely and the exploit is publicly available.
Original NVD description (English source)
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 data from NVD (NIST) · CISA KEV · EPSS