Moodle PDF Annotator plugin v1.5 release 9 allows stored cross-site scripting (XSS) via the Public Comments feature. An attacker with a low-privileged account (e.g., Student) can inject arbitrary JavaScript payloads into a comment. When any other user (Student, Teacher, or Admin) views the annotated PDF, the payload is executed in their browser, leading to session hijacking, credential theft, or other attacker-controlled actions.