MediaWiki before 1.15.3, and 1.6.x before 1.16.0beta2, does not properly handle a correctly authenticated but unintended login attempt, which makes it easier for remote authenticated users to conduct phishing attacks by arranging for a victim to login to the attacker's account and then execute a crafted user script, related to a "login CSRF" issue.
The web application does not, or cannot, sufficiently verify whether a request was intentionally provided by the user who sent the request, which could have originated from an unauthorized actor.