MediaWiki before 1.15.2 does not prevent wiki editors from linking to images from other web sites in wiki pages, which allows editors to obtain IP addresses and other information of wiki users by adding a link to an image on an attacker-controlled web site, aka “CSS validation issue.”
lists.opensuse.org/opensuse-security-announce/2010-04/msg00006.html
lists.wikimedia.org/pipermail/mediawiki-announce/2010-March/000088.html
secunia.com/advisories/39022
secunia.com/advisories/39656
www.debian.org/security/2010/dsa-2022
www.vupen.com/english/advisories/2010/0685
www.vupen.com/english/advisories/2010/1001