GHSA-vgp4-2fc4-qff2 is a high-severity (CVSS 8.1) Cross-site Scripting (XSS) vulnerability in winter/wn-backend-module. A fix is available for winter/wn-backend-module — see the affected versions and patch details below.
Winter: Stored XSS through Editor Settings custom styles
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-vgp4-2fc4-qff2.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
GHSA-vgp4-2fc4-qff2 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 379,842 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
winter/wn-backend-moduleReal-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
Authenticated Backend Users with the backend.manage_editor ("Manage editor settings") permission can provide custom styles through Settings → Editor Settings → Markup Styles that are 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.manage_editor permission only be granted to trusted administrators and developers.
A related issue exists in the custom CSS field at Settings → Customize Backend → Styles (backend.manage_branding permission), which uses the same rendering mechanism and is addressed separately.
All users are advised to update to the latest version to ensure their systems remain secure.
Patches
This issue has been patched in v1.2.13. The renderCss() method now applies strip_tags() to compiled CSS output before returning it.
Workarounds
Apply https://github.com/wintercms/winter/commit/d28f0b9474af79cfaa80eeb9d691f7a7c4469720 manually if unable to upgrade to v1.2.13.
Resources
- CVE-2025-61674 (identical vulnerability in October CMS, patched in v3.7.13 and v4.0.12)
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | winter/wn-backend-module | ≥ 1.2.10&&< 1.2.13 | 1.2.13composer require winter/wn-backend-module:^1.2.13 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for winter/wn-backend-module, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
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 GHSA-vgp4-2fc4-qff2 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
Frequently Asked Questions
Is GHSA-vgp4-2fc4-qff2 in your dependencies?
Find it across Packagist, including transitive dependencies.