Summary
The addTeacher() lacks some missing logic where the principal can add themselves as the teacher

Vulnerability Details
if the principal is malicious or compromised, they can themselves as the teacher since they have access control

Impact
the impact may be low, since adding themselves may just create confusion and no direct impact

Tools Used

manual review

Recommendations
consider adding the logic that even if the principal has the sole acces control, they cannot add themselves as the teacher