Your RSA-2048 keys break in 2030. Find every one of them before attackers do.
🐘 Packagist
Not in CISA KEV

CVE-2026-35445

CVE-2026-35445 is a security vulnerability in winter/wn-backend-module. O3 Security confirms whether CVE-2026-35445 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.

Winter: Authenticated backend users can bypass Users controller permission checks

Published
Aug 12, 2026
Updated
Aug 12, 2026
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Aug 12, 2026 · OSV.dev, FIRST.org (EPSS)

Real-World Exposure

1 pkg affected
🐘winter/wn-backend-module

Real-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

Affected versions of Winter CMS did not validate the handler name submitted through the form postback mechanism (_handler POST field) in the same way as AJAX requests (X_WINTER_REQUEST_HANDLER header). The AJAX path validates that handler names match the on[A-Z][\w+]* pattern, but the postback path passed the handler name directly to the handler dispatcher with no validation.

This allowed an authenticated backend user to call any method on a controller — including action-prefixed, protected, and private methods — by submitting a crafted POST request with a _handler field, as long as the controller either:

  • Contains a publicly available action via the $publicActions property, or
  • Degrades or removes the $requiredPermissions check in its constructor based on a condition

The backend's own Users controller was affected by the second scenario: it set $requiredPermissions to null for the myaccount action, allowing any authenticated backend user to access the controller without the backend.manage_users permission. Combined with the postback bypass, this allowed calling controller methods such as update_onDelete, update_onRestore, update_onUnsuspendUser, and update_onManualPasswordReset with attacker-controlled parameters.

Note that CSRF tokens are still verified on all POST requests, so the attacker must be logged into the backend with a valid session.

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).

Patches

The postback handler path now validates handler names using the same rules as the AJAX path. The My Account functionality has been moved to a dedicated controller that does not expose user management methods. Defence in depth has been applied at the model level to prevent unauthorized user record modifications regardless of the entry point.

This security issue has been fixed as of v1.2.13.

Workarounds

If users cannot upgrade, they may apply the following changes to their Winter CMS installation manually to resolve this issue:

  1. In modules/backend/classes/Controller.php, validate the _handler POST field against the on[A-Z][\w+]* pattern before passing it to runAjaxHandler().
  2. In modules/backend/controllers/Users.php, remove the conditional that sets $requiredPermissions to null for the myaccount action.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐘Packagistwinter/wn-backend-moduleall versions1.2.13

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for winter/wn-backend-module. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

  2. 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 CVE-2026-35445 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

  4. How O3 protects you

    O3 pinpoints whether CVE-2026-35445 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to CVE-2026-35445. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

### Impact Affected versions of Winter CMS did not validate the handler name submitted through the form postback mechanism (`_handler` POST field) in the same way as AJAX requests (`X_WINTER_REQUEST_HANDLER` header). The AJAX path validates that handler names match the `on[A-Z][\w+]*` pattern, but the postback path passed the handler name directly to the handler dispatcher with no validation. This allowed an authenticated backend user to call any method on a controller — including action-prefixed, protected, and private methods — by submitting a crafted POST request with a `_handler` field,
O3 Security · Impact-Aware SCA

Is CVE-2026-35445 in your dependencies?

O3 detects CVE-2026-35445 across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

Scan my dependencies How O3 SCA works