Strapi Upload Plugin MIME Validation Bypass via Content API

Summary

Strapi is an open source headless content management system. In Strapi versions prior to 5.33.3, the Upload plugin's Content API endpoints did not enforce the administrator-configured MIME type restrictions (`plugin.upload.security.allowedTypes` and `deniedTypes`). The same restrictions were correctly enforced on the Admin Panel upload path. The upload plugin's `enforceUploadSecurity` security check was invoked in the admin upload controller but was missing from the Content API controller. The Content API handlers `uploadFiles` and `replaceFile` (and the `upload` wrapper that dispatches to them) called the underlying upload service directly, bypassing both the magic-byte MIME detection and the configured allow/deny lists. An authenticated user with the Content API upload permission could therefore upload file types the administrator had explicitly disallowed, including HTML and SVG content. In deployments serving uploaded files from the same origin as the admin panel (default), an attacker could upload an HTML or SVG file that, when opened directly by an admin, executed JavaScript in the admin origin, enabling admin-session hijack and authenticated administrative actions against the admin API. The patch in version 5.33.3 introduces a shared `prepareUploadRequest` helper that wraps `enforceUploadSecurity` and is called from both the Content API and admin upload controllers, ensuring identical security policy enforcement on every upload entry point.

Timeline

1. May 14, 2026, 6:40 PM UTCCVE published
2. May 14, 2026, 7:39 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: yes · Technical impact: partial

3. May 14, 2026, 7:40 PM UTCRecord last updated

Affected versions

• strapi strapi

  fixed in 5.33.3

• strapi @strapi/upload

  fixed in 5.33.3

• @strapi/uploadnpm

  fixed in 5.33.3

References 1