CVE-2026-35445 Overview
CVE-2026-35445 is an authorization bypass vulnerability in Winter CMS, a content management system built on the Laravel PHP framework. Versions prior to 1.2.13 fail to validate the _handler field submitted through form postbacks in the backend. An authenticated backend user can invoke arbitrary controller methods, including protected, private, and action-prefixed handlers, circumventing the roles and permissions system. The built-in Users controller is directly affected because it sets $requiredPermissions to null for the myaccount action, exposing user-management methods such as update_onDelete and update_onManualPasswordReset to any authenticated backend user. The issue is classified as [CWE-285: Improper Authorization].
Critical Impact
Any authenticated backend user can invoke privileged user-management operations without holding the backend.manage_users permission, enabling horizontal and vertical privilege escalation within the CMS.
Affected Products
- Winter CMS versions prior to 1.2.13
- Winter CMS backend module (form postback handler dispatcher)
- Winter CMS built-in Users controller (myaccount action path)
Discovery Timeline
- 2026-08-26 - CVE-2026-35445 published to NVD
- 2026-08-26 - Last updated in NVD database
- Fixed - Winter CMS release v1.2.13
Technical Details for CVE-2026-35445
Vulnerability Analysis
Winter CMS dispatches backend actions through two request paths: AJAX requests and traditional form postbacks. The AJAX path enforces that handler names match the on[A-Z][\w+]* naming convention, restricting invocation to conventional AJAX event handlers. The postback path does not apply this restriction. It forwards the client-supplied _handler value directly to the handler dispatcher.
This inconsistency lets an authenticated backend user submit any method name as the handler for a controller. Any controller that exposes a public action, or one that conditionally relaxes its $requiredPermissions check, becomes reachable through the postback path. The permission model that gates AJAX event handlers is effectively bypassed for the postback dispatcher.
Root Cause
The root cause is missing input validation on the _handler POST field in the postback flow. The AJAX flow validates handler names against a regular expression, but the postback flow trusts the submitted value. Combined with controllers that scope $requiredPermissions to specific actions, this asymmetry breaks the intended authorization boundary.
Attack Vector
An attacker requires an authenticated backend session with any role. The attacker crafts a form POST to a backend controller endpoint whose action clears required permissions, such as the Users controller myaccount action. The _handler field is set to a privileged method name such as update_onDelete or update_onManualPasswordReset. The dispatcher invokes the method, allowing the attacker to delete users or reset passwords without holding the backend.manage_users permission.
See the GitHub Security Advisory GHSA-j5jq-cr68-v2xx and the remediation pull request #1473 for the authoritative technical breakdown.
Detection Methods for CVE-2026-35445
Indicators of Compromise
- Backend POST requests containing a _handler field whose value does not match the on[A-Z][\w+]* AJAX handler pattern.
- Invocations of user-management methods such as update_onDelete, update_onManualPasswordReset, or other update_on* handlers originating from accounts without the backend.manage_users permission.
- Unexpected user deletions, password resets, or role changes performed by non-administrative backend accounts.
Detection Strategies
- Inspect web server and application logs for POST requests to backend controller routes where the _handler parameter references protected or private controller methods.
- Correlate backend audit events for user modifications with the acting user's assigned permissions to identify actions taken without backend.manage_users.
- Alert on repeated postbacks from a single session that target multiple sensitive handler names, indicating enumeration of controller methods.
Monitoring Recommendations
- Enable verbose backend request logging in Winter CMS to capture the full _handler value and originating user for each postback.
- Forward CMS access logs and Laravel application logs to a centralized log platform for retention and rule-based alerting.
- Baseline the set of handler names invoked by each backend role and alert on deviations from that baseline.
How to Mitigate CVE-2026-35445
Immediate Actions Required
- Upgrade Winter CMS to version 1.2.13 or later, which enforces handler-name validation on the postback path.
- Audit backend user accounts and remove or downgrade any accounts that do not require backend access.
- Review recent backend activity logs for unauthorized user deletions, password resets, or role modifications performed since deployment of an affected version.
Patch Information
The fix is included in Winter CMS v1.2.13. The patch, delivered in pull request #1473, applies the same handler-name pattern validation used on the AJAX path to the form postback dispatcher, rejecting _handler values that do not conform to the on[A-Z][\w+]* convention. See the GitHub Security Advisory GHSA-j5jq-cr68-v2xx for the coordinated disclosure record.
Workarounds
- Restrict backend access to trusted administrators only until the upgrade to 1.2.13 is completed.
- Place the backend behind network controls such as an IP allowlist, VPN, or reverse proxy authentication to reduce the attacker population able to reach the vulnerable endpoint.
- Review custom controllers for any use of conditional $requiredPermissions relaxation and enforce explicit permission checks inside sensitive handler methods.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
