Winter CMS is a content management system built on the Laravel PHP framework. In versions up to and including 1.2.12, the backend FileUpload form widget trusted an attacker-controlled file_id POST parameter when resolving the attachment it operates on, allowing an authenticated backend user to read and modify attachment records belonging to other users or records. The widget's getFileRecord() lookup resolved the posted id against the global system_files table without verifying that the file belonged to the widget's own relation, parent record, or deferred-binding session. Because all attachments share a single File model and table and attachment ids are sequential integers that are easily enumerated, a user reaching any form with a fileupload field, including the built-in My Account avatar field that requires no specific permission, could target arbitrary attachments to modify their title and description via onSaveAttachmentConfig and change their sort order via onSortAttachments, which passed posted ids straight to an unscoped update. CSRF tokens remain enforced, so exploitation requires a valid authenticated backend session with any level of access. This issue is fixed in version 1.2.13.

Affected: Packagist: winter/wn-backend-module

### Impact

The backend `FileUpload` form widget trusted an attacker-controlled `file_id` POST parameter when resolving the attachment it operates on. The lookup (`FileUpload::getFileRecord()`) resolved the posted id against the global `system_files` table without verifying that the file belonged to the widget's own relation, parent record, or deferred-binding session.

Any authenticated backend user who can reach a form containing a `fileupload` field — including the built-in **My Account** avatar field, which requires no specific backend permission — could therefore target a `System\Models\File` record belonging to another user or record and:

- modify its `title` and `description` via `onSaveAttachmentConfig`, and - change its `sort_order` via `onSortAttachments` (which passed posted ids straight to `setSortableOrder()`, an unscoped `UPDATE ... WHERE id = ?`).

The same unscoped lookup is reached by `onLoadAttachmentConfig`, `onSaveAttachmentConfig`, and `onRemoveAttachment`. Because all attachments share the single `System\Models\File` model and `system_files` table, an attacker was not limited to other users' avatars — any attachment on any model could be referenced by id. Attachment ids are sequential integers and are easily enumerated.

The confirmed impact is unauthorized integrity modification of arbitrary attachment metadata and ordering.

CSRF tokens are still verified on all POST requests, so an attacker must be authenticated to the backend with a valid session…