WordPress.org have released Version 3.4.2 update that fixes security issues and bugs.
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.
Version 3.4.2 also fixes a few security issues and contains some security hardening. The vulnerabilities included potential privilege escalation and a bug that affects multisite installs with untrusted users. These issues were discovered and fixed by the WordPress security team.
Further information about the update, including a full list of fixes and changed files can be found on the Codex pages at: http://codex.wordpress.org/Version_3.4.2
