Summary
Winter: Stored XSS through Brand Settings custom styles
Workarounds
Apply https://github.com/wintercms/winter/commit/d28f0b9474af79cfaa80eeb9d691f7a7c4469720 manually if unable to upgrade to v1.2.13.
Resources
- CVE-2025-61676 (identical vulnerability in October CMS, patched in v3.7.13 and v4.0.12)
Impact
Users with the backend.manage_branding ("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.manage_branding 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.manage_editor 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.
Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.
CVE-2026-32257 has a CVSS score of 8.1 (High). The vector is network-reachable, high privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.2.13); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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This issue has been patched in v1.2.13.
Frequently Asked Questions
- What is CVE-2026-32257? CVE-2026-32257 is a high-severity cross-site scripting (XSS) vulnerability in winter/wn-backend-module (composer), affecting versions <= 1.2.12. It is fixed in 1.2.13. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
- How severe is CVE-2026-32257? CVE-2026-32257 has a CVSS score of 8.1 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of winter/wn-backend-module are affected by CVE-2026-32257? winter/wn-backend-module (composer) versions <= 1.2.12 is affected.
- Is there a fix for CVE-2026-32257? Yes. CVE-2026-32257 is fixed in 1.2.13. Upgrade to this version or later.
- Is CVE-2026-32257 exploitable, and should I be worried? Whether CVE-2026-32257 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-32257 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-32257? Upgrade
winter/wn-backend-moduleto 1.2.13 or later.