CVE-2026-35445 wintercms CVE debrief

Who should care

Authenticated backend users of Winter CMS versions prior to 1.2.13 should verify their permissions and validate handler names to prevent unauthorized actions. Operators, administrators, and security teams managing Winter CMS deployments should review and apply the necessary patches or mitigations.

Why it matters

CVE-2026-35445 is a high-severity vulnerability in Winter CMS that allows authenticated backend users to invoke arbitrary controller methods, potentially leading to unauthorized actions and privilege escalation.

• Potential unauthorized actions by authenticated backend users
• Bypass of roles and permissions system
• Invocation of arbitrary controller methods
• Possible elevation of privileges

Technical summary

The vulnerability in Winter CMS versions prior to 1.2.13 allows authenticated backend users to invoke arbitrary controller methods, including protected and private ones, due to insufficient validation of the handler name submitted through the form postback _handler POST field. This issue arises from the backend's failure to validate the handler name, permitting an authenticated backend user to invoke arbitrary controller methods. The built-in Users controller was affected because it set $requiredPermissions to null for the myaccount action.

Defensive priority

Authenticated users with backend access should verify their permissions and validate handler names to prevent unauthorized actions.

Recommended defensive actions

• Verify and validate handler names in Winter CMS versions prior to 1.2.13
• Restrict permissions for authenticated backend users
• Upgrade to Winter CMS version 1.2.13 or later
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.
• Review compensating controls for exposed systems while remediation is scheduled and verified.
• Check relevant monitoring, detection, and logs for exposed assets that need extra review.
• Track exceptions, retest remediated assets, and close the item only after evidence is documented.

Evidence notes

The CVE record and NVD entry provide details on the vulnerability, including its description, CVSS score, and affected versions. The vulnerability was fixed in version 1.2.13. Authenticated backend users of Winter CMS versions prior to 1.2.13 should verify their permissions and validate handler names to prevent unauthorized actions. The CVE Program record and NVD detail page offer official information on CVE-2026-35445.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.