Pagekit CMS 1.0.18 Privilege Escalation via UserApiController

Pagekit CMS 1.0.18 contains a privilege escalation vulnerability that allows authenticated users with the 'user: manage users' permission to escalate privileges by assigning arbitrary custom roles to themselves due to missing authorization checks in UserApiController::saveAction(). Attackers can assign themselves a custom role with the 'system: manage packages' permission and then upload and install a malicious PHP package through the admin package installer to achieve remote code execution.