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MEDIUM severity

CVE-2026-54256

MEDIUMFix: wintercms/winter@9cb0ae5

CVE-2026-54256 is a medium-severity (CVSS 5.4) vulnerability in winter/wn-backend-module. O3 Security confirms whether CVE-2026-54256 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.

Winter: Authenticated IDOR in backend FileUpload widget allows cross-user access to attachment metadata

Published
Aug 20, 2026
Updated
Aug 20, 2026
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Aug 20, 2026 · OSV.dev, FIRST.org (EPSS)

Real-World Exposure

1 pkg affected
🐘winter/wn-backend-module

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

Description

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. To exploit this issue an attacker needs a backend account with any level of access.

Patches

The FileUpload widget now scopes every file_id lookup to the widget's own relation, including any files bound through the current deferred-binding session, so a posted id can no longer reference an unrelated System\Models\File record:

  • getFileRecord() resolves the id through getRelationObject()->withDeferred($this->sessionKey)->find(...) rather than the global file model. This covers onLoadAttachmentConfig, onSaveAttachmentConfig, and onRemoveAttachment.
  • onSortAttachments() intersects the posted ids with the ids that actually belong to the relation before calling setSortableOrder().

This security issue has been fixed as of v1.2.13 (commit 9cb0ae5f9d837db141ab111c6a7de8eed9603d25).

Workarounds

There is no supported workaround other than upgrading. If you cannot upgrade immediately, you may apply the fix manually in modules/backend/formwidgets/FileUpload.php:

  1. In getFileRecord(), replace $this->getRelationModel()->find(post('file_id')) with $this->getRelationObject()->withDeferred($this->sessionKey)->find(post('file_id')).
  2. In onSortAttachments(), filter the posted sortOrder ids to those returned by $this->getRelationObject()->withDeferred($this->sessionKey)->pluck($keyName) before calling setSortableOrder().

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐘Packagistwinter/wn-backend-moduleall versions1.2.13

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for winter/wn-backend-module. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

  2. Fix

    Update winter/wn-backend-module to 1.2.13 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-54256 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

  4. How O3 protects you

    O3 pinpoints whether CVE-2026-54256 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to CVE-2026-54256. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

### 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\F
O3 Security · Impact-Aware SCA

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