fix: sandbox served course assets to prevent stored XSS - #481
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Studio course assets are served by the contentserver with the uploader-supplied Content-Type and no neutralizing headers, on a route mounted on the Studio (CMS) origin. An author with file-upload permission can upload an HTML or SVG file containing script; when another user opens the asset URL it runs same-origin with the Studio session, enabling privilege escalation (self-granting course-admin, or Django superuser via same-origin /admin/ when a global-staff user views it). Send `Content-Security-Policy: sandbox` on every course-asset response so the asset loads in an opaque origin and cannot script against the Studio/LMS session. A per-course escape-hatch flag, course_assets.allow_unsafe_asset_rendering, lets operators temporarily disable sandboxing for a course whose content must be migrated first. Closes GHSA-c6xg-fh3c-vvhh. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> (cherry picked from commit 2efdce0)
vgulati-apphelix
approved these changes
Sep 21, 2026
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Description
This PR backports the upstream security fix for GHSA-c6xg-fh3c-vvhh / CWE-434 / CWE-79 to downstream.
Cherry-picked from upstream commit:
2efdce0760561db2bcd3a2895c93480d01f0a308.Vulnerability Summary
Course assets uploaded in Studio (CMS) were served inline by
contentserverusing attacker-controlled MIME types without restricted headers or a sandboxing CSP. This allowed malicious course staff to upload.htmlor.svgfiles containing JavaScript, resulting in Stored Cross-Site Scripting (XSS) and privilege escalation when viewed by administrators or instructors.Fix
Adds
Content-Security-Policy: sandboxheader to asset server responses inopenedx/core/djangoapps/contentserver/views.py. This forces the browser to treat rendered assets as an isolated, opaque origin with script execution and session access disabled.Ticket
LP-1255