CVE-2026-54256 Winter: Authenticated IDOR in backend FileUpload widget allows cross-user access to attachment metadata
Authenticated users can read and modify other users' attachment metadata due to missing authorization checks in the FileUpload widget.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-54256?
CVE-2026-54256 is a medium-severity missing authorization vulnerability in wintercms winter, published on 26 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
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.
Which versions are affected by CVE-2026-54256?
2 open source packages ship an affected version, including winter/wn-backend-module.
| Package | Affected | Fixed in |
|---|---|---|
winter/wn-backend-module Packagist | All versions | 1.2.13 |
winter/wn-backend-module Packagist | All versions | 1.2.13 |
How do I fix CVE-2026-54256?
Upgrade winter/wn-backend-module to 1.2.13 or later.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-54256 being exploited?
There is no known exploitation of CVE-2026-54256 in the wild and no public exploit code.
Sources
Also known as GHSA-3277-h8g9-qj5f.