MediaWiki before 1.19.10, 1.2x before 1.21.4, and 1.22.x before 1.22.1 allows remote attackers to obtain information about deleted page via the (1) log API, (2) enhanced RecentChanges, and (3) user watchlists.
http://lists.wikimedia.org/pipermail/mediawiki-announce/2014-January/000138.html