Executive brief
fastschema is a backend-as-a-service platform with a headless CMS. An authenticated user with low privileges can upload a malicious SVG file containing JavaScript code that bypasses the system's file type restrictions, leading to stored XSS attacks that execute when other users view the uploaded file.
Technical details
This is a stored cross-site scripting (XSS) vulnerability in fastschema through v0.15.1 caused by insufficient validation of SVG file uploads. The application attempts to enforce MIME type restrictions via an allow-list, but attackers can bypass this check by uploading an SVG file with embedded malicious JavaScript. The vulnerability requires authentication with low-level privileges to exploit. When another user or administrator views the uploaded SVG file through the application interface, the embedded JavaScript executes in their browser context, potentially allowing session hijacking, credential theft, or other malicious actions. Patches are expected to be available in versions after v0.15.1.
Affected products
- fastschema fastschema through v0.15.1
Timeline
- 2026-08-10: disclosed: CVE-2026-72583 published