Cross-site scripting (XSS) vulnerability in pages/TalkpageHistoryView.php in the LiquidThreads (LQT) extension 2.x and possibly 3.x for MediaWiki 1.19.x before 1.19.8, 1.20.x before 1.20.7, and 1.21.x before 1.21.2 allows remote attackers to inject arbitrary web script or HTML via a thread subject.