MediaWiki before 1.19.24, 1.2x before 1.23.9, and 1.24.x before 1.24.2, when using HHVM or Zend PHP, allows remote attackers to cause a denial of service ("quadratic blowup" and memory consumption) via an XML file containing an entity declaration with long replacement text and many references to this entity, a different vulnerability than CVE-2015-2942.