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High, CVSS 8.1amended

Winter: Stored XSS through Brand Settings custom styles

CVE-2026-32257GHSA-v7cf-8gh9-gxmj

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (winter/wn-backend-module 1.2.13), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
8.1 · CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:H/I:H/A:N
EPSS
  • CVE-2026-32257: 0.38% estimated exploitation activity in the next 30 days; percentile 32.26 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Impact Users with the backend.managebranding ("Customize the back-end") permission can provide custom CSS through Settings → Customize Backend → Styles that is compiled through the LESS CSS parser and rendered on every backend page. Previously, the compiled output was not sanitized, which could have allowed a stored XSS attack. Although this is a valid security issue, it's important to note that its severity is relatively low. To exploit the vulnerability, an attacker would already need to have trusted access to the Winter CMS backend with a specific administrative permission. The Winter CMS maintainers recommend that the backend.managebranding permission only be granted to trusted administrators and developers. A related issue exists in the custom styles field at Settings → Editor Settings → Markup Styles (backend.manageeditor permission), which uses the same rendering mechanism and is addressed separately. All users are advised to update to the latest version to ensure their…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-v7cf-8gh9-gxmj

  2. Revision 1 · created ·

    Published from osv record GHSA-v7cf-8gh9-gxmj

Agent brief

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# Patch Next advisory brief: CVE-2026-32257

Advisory: Winter: Stored XSS through Brand Settings custom styles
IDs: CVE-2026-32257, GHSA-v7cf-8gh9-gxmj
Record: https://patchnext.com/advisories/cve-2026-32257 (revision 2, source checked 26 Oct 2026, 14:50 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: winter/wn-backend-module 1.2.13. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist winter/wn-backend-module: affected <= 1.2.12; fixed in 1.2.13

## Suggested inspection (read-only)
- Packagist winter/wn-backend-module: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on winter/wn-backend-module.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-v7cf-8gh9-gxmj (OSV record GHSA-v7cf-8gh9-gxmj lists affected ranges: Packagist winter/wn-backend-module >=0 <1.2.13 (fixed))
- Verified: https://github.com/advisories/GHSA-v7cf-8gh9-gxmj (GitHub-reviewed advisory GHSA-v7cf-8gh9-gxmj lists affected ranges: Packagist winter/wn-backend-module >=0 <=1.2.12)

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