CVE-2026-29056: Improperly Controlled Modification of Dynamically-Determined Object Attributes

Kanboard is project management software focused on Kanban methodology. Prior to 1.2.51, Kanboard's user invite registration endpoint (`UserInviteController::register()`) accepts all POST parameters and passes them to `UserModel::create()` without filtering out the `role` field. An attacker who receives an invite link can inject `role=app-admin` in the registration form to create an administrator account. Version 1.2.51 fixes the issue.