A very brief announcement was sent to the mailing list. "Today Oracle released VirtualBox 4.2.6, a maintenance release of VirtualBox 4.2 which improves stability and fixes regressions."
The VirtualBox 4.2.6 specific fixes though are mentioned on the VirtualBox.org Change-log. Among the changes are several 3D support fixes, VMM fixes, GUI enhancements, storage improvements, minor work on VBoxManage, and a couple of changes pertaining to the Linux Additions support.
Oracle VirtualBox 4.2.6 is available for all major operating systems and can be downloaded at VirtualBox.org.