Google Chrome before 6.0.472.53 does not properly handle the _blank value for the target attribute of unspecified elements, which allows remote attackers to bypass the pop-up blocker via unknown vectors.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A11752
http://googlechromereleases.blogspot.com/2010/09/stable-and-beta-channel-updates.html