Fix stored XSS in renderer (mdlshield finding) - #138
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Escape teacher-authored answer text before emitting it into HTML. Three paths in renderer.php rendered raw content to students: setup_answeroptions() draggable list and get_aftergap_text() right-answer display are now escaped with s(), and get_feedback() runs strip_tags output through clean_text() to remove event-handler attributes and javascript: URLs that strip_tags leaves on allowed tags. Add walkthrough regression tests asserting an <img onerror> payload is escaped in the draggable list and the after-gap right-answer.
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Fixes a stored XSS reported by the mdlshield automated review (HIGH severity). Teacher-authored gap content and correct-answer display text were concatenated into HTML in
renderer.phpwithout escaping, so a payload such as[<img src=x onerror=...>]executed in any student's browser.Three paths fixed:
setup_answeroptions()- draggable answer list now built withhtml_writer::tag+s().get_aftergap_text()- right-answer display now escaped withs().get_feedback()-strip_tagsleft event-handler attributes (onclick,onerror,javascript:hrefs) on allowed tags; the output now runs throughclean_text()which strips them.Tests: added two walkthrough regression tests asserting an
<img onerror>payload is escaped (raw payload absent,s()-escaped form present) in both the draggable list and the after-gap right-answer display. Full gapfill suite passes:walkthrough_test24/24, plusquestion_test,questiontype_test,backup_testgreen.