What is the ruling on a teacher kissing his student on the mouth, cheek, and neck, given that the student feels sinful and is unable to confront the teacher?

What the teacher is doing by kissing is a great evil (munkar), and he must not be allowed to do that. The impermissibility of his action must be clarified to him, and he should be threatened with informing the parents if he does not stop. If he does not desist, then inform whoever is able to prevent him. If that is not possible, then leave him and seek another teacher. Be careful not to be complacent in this matter. Seek Allah's help and reject the whispers of Satan.