Maintenance and Security Release

*Fix some issues with older browsers in the administration area.
*Fix an issue where a theme may not preview correctly, or its screenshot may not be displayed.
*Improve plugin compatibility with the visual editor.
*Address pagination problems with some category permalink structures.
*Avoid errors with both oEmbed providers and trackbacks.
*Prevent improperly sized header images from being uploaded.

More here
http://wordpress.org/news/
http://wordpress.org/download/
http://wordpress.org/news/2012/09/wordpress-3-4-2/