CVE-2026-27591

Workarounds

If you cannot upgrade, you may apply the changes from the releases to your Winter CMS installation manually to resolve this issue.

Affected versions of Winter CMS allowed authenticated backend users to escalate their accounts level of access to the system by modifying the roles / permissions assigned to their account through specially crafted requests to the backend while logged in.

To actively exploit this security issue, an attacker would need access to the Backend with a user account with any level of access.

The Winter CMS maintainers strongly recommend that all Winter CMS sites that have any reliance on the roles & permissions system to update immediately. Security fixes have been backported to all major versions of Winter (1.0, 1.1, and 1.2).

CVE-2026-27591 has a CVSS score of 9.9 (Critical). The vector is network-reachable, low privileges required, and no user interaction. 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 (1.2.12, 1.1.12, 1.0.477); upgrading removes the vulnerable code path.

Kodem intelligence

Multiple fixes and defence in depth has been applied to prevent current and future privilege escalation attacks at the lowest level possible.

This security issue has been fixed as of https://wintercms.com/releases/v1.0.477, https://wintercms.com/releases/v1.1.12, https://wintercms.com/releases/v1.2.12.

1. What is CVE-2026-27591? CVE-2026-27591 is a critical-severity security vulnerability in winter/wn-backend-module (composer), affecting versions >= 1.2.0, < 1.2.12. It is fixed in 1.2.12, 1.1.12, 1.0.477.
2. How severe is CVE-2026-27591? CVE-2026-27591 has a CVSS score of 9.9 (Critical). 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.
3. Which versions of winter/wn-backend-module are affected by CVE-2026-27591? winter/wn-backend-module (composer) versions >= 1.2.0, < 1.2.12 is affected.
4. Is there a fix for CVE-2026-27591? Yes. CVE-2026-27591 is fixed in 1.2.12, 1.1.12, 1.0.477. Upgrade to this version or later.
5. Is CVE-2026-27591 exploitable, and should I be worried? Whether CVE-2026-27591 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
6. What actually determines whether CVE-2026-27591 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.
7. How do I fix CVE-2026-27591?
   • Upgrade winter/wn-backend-module to 1.2.12 or later
   • Upgrade winter/wn-backend-module to 1.1.12 or later
   • Upgrade winter/wn-backend-module to 1.0.477 or later