A flaw was found in Foreman’s Api::V2::MailNotificationsController, where authorization checks on user-specific mail-notification resources are insufficient. The GET /api/v2/users/:id/mail_notifications endpoint resolves the target account using User.find(params[:id]) without verifying that the authenticated user is authorized to access that user’s notification configuration. Additionally, the POST and PUT /api/v2/users/:user_id/mail_notifications paths call deny_access when the requester is unauthorized but fail to halt execution, allowing the request to continue and persist the unauthorized change despite a 403 response or subsequent DoubleRenderError. This can allow a user to disclose another user’s mail-notification configuration, including mail_query values, and, where write permissions apply, modify or create notification settings for another user.