GHSA-mpmw-f6h6-3g26: Winter: My Account preview exposes another backend user's profile by record ID

Backend\Controllers\MyAccount, introduced in v1.2.13, declares an empty $requiredPermissions array so that any authenticated backend user can manage their own account. It implements the FormController behavior, which exposes three routable actions — create, update and preview — that each take a record id from the URL.

index() passes the authenticated user’s own id to the behavior, but the inherited actions were left routable and formFindModelObject() was not scoped, so a caller-supplied id resolved against an unscoped Backend\Models\User query:

GET /backend/backend/myaccount/preview/{other_user_id}

preview disclosed the target user’s first name, last name, login, email address and avatar; update was equally routable and additionally disclosed role, group membership, superuser flag and throttle state. Password controls render a mask, so no credential material was exposed. Backend user ids are sequential and trivially enumerated, and as these are GET actions no CSRF token is involved.

The behavior’s AJAX handlers (create_onSave, update_onSave, update_onDelete) were also dispatchable on these routes, but cross-user writes were blocked by the Backend\Models\User authorization guards added in v1.2.13. The confirmed impact is unauthorized disclosure of backend user profile data.

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