Laravel Backpack CRUD: HasUploadFields keeps the attacker-supplied file extension — public-disk uploads of `shell.php` reach the webserver

Summary

HasUploadFields (used via CrudTrait on Backpack-managed models) and the withFiles() uploader preserve the client-supplied file extension without validation. On installations using a public disk with php artisan storage:link, this allows an authenticated administrator to upload a file with a server-executable extension that the web server will pass to the PHP interpreter - if no MIME or other type of upload validation is present.

Details

The uploadFileToDisk and uploadMultipleFilesToDisk methods hash the filename stem but write the client-supplied extension to disk verbatim — no allowlist, blocklist, or MIME check is applied inside the trait itself.

The newer withFiles() path (via FileNameGenerator) resolves the extension from the file's MIME type rather than the client filename, but also does not block server-executable types.

Applications that follow the Backpack quickstart without adding explicit mimes: or mimetypes: validation rules in their form requests are affected.

Impact

An authenticated administrator with access to an upload-enabled CRUD panel, on a site using the public disk with web-accessible storage and no MIME type validation, can upload a server-executable file and achieve remote code execution.

Conditions required for exploitation:

• Authenticated admin access to a Backpack CRUD panel
• An upload field with no mimes: / mimetypes: validation rule
• The public disk in use (standard pattern for web-visible uploads)
• php artisan storage:link in place
• A web server + PHP-FPM stack (default on most hosts)

Fix

A denylist for server-executable extensions has been added to both HasUploadFields and FileNameGenerator. Image-typed fields now additionally enforce an allowlist. This is defence-in-depth — it does not replace application-level validation.

Recommended developer action

Review all upload fields and add explicit mimes: or mimetypes: validation in your form requests or field definitions. Refer to the Backpack field documentation for examples.

Reported by Vishal Shukla (@shukla304) via sechub.dev.