MediaWiki is a collaborative editing software, used by big projects like Wikipedia.
MediaWiki incorrectly handles page template inclusions, rendering it vulnerable to cross-site scripting attacks.
A remote attacker could exploit this vulnerability to inject malicious script code that will be executed in a user's browser session in the context of the vulnerable site.
There is no known workaround at this time.
All MediaWiki users should upgrade to the latest available versions:
# emerge --sync
# emerge --ask --oneshot --verbose www-apps/mediawiki