MediaWiki is prone to an HTML-injection vulnerability because the application fails to properly sanitize user-supplied input. An attacker may leverage this issue to execute arbitrary script code in the browser of an unsuspecting user in the context of the affected site. This may help the attacker steal cookie-based authentication credentials and launch other attacks. MediaWiki versions 1.9.0 prior to 1.9.2 are vulnerable to this issue. Reproducible: Didn't try http://svn.wikimedia.org/svnroot/mediawiki/tags/REL1_9_2/phase3/RELEASE-NOTES
1.9.2 is now commited, I was simply waiting for the tar ball to be present and confirm it's md5.
Note 2, please check that 1.8.x is really affected, as there is not metion of this for those versions.
1.8 is not known to be vulnerable, closing