Oracle today released VirtualBox 4.0, a maintenance release of VirtualBox 4.0. It improves stability and fixes regressions.

This is a maintenance release. The following items were fixed and/or added:

GUI: don't crash if a removable host drive referenced from the VM settings vanished
GUI: fixed a crash when using the KDE4 Oxygen theme and clicked on the settings button (4.0 regression; bug #7875)
GUI: properly warn if the machine folder cannot be created (bug #8031)
GUI: several fixes for multimonitor X11 guests
ExtPack: don’t make the installer helper application suid root (Linux .deb/.rpm packages only)
ExtPack: improved user experience on Vista / Windows 7 when installing an extension pack
ExtPack: fixed issue with non-ascii characters in the path name during installing an extension pack (bug #7917)
ExtPack: fixed SELinux issues on 32-bit Linux hosts
VBoxManage: Host-only interface creation and removal is now supported for all platforms except Solaris (bug #7741)
VBoxManage: fixed segmentation fault when removing non-existent host-only interface
Storage: fixed possible crashes with VMDK/VHD images with snapshots and async I/O (4.0 regression)
Storage: don’t eject the physical medium if a DVD/CDROM/floppy drive is detached from a VM (bug #5825)
Storage: be more robust when a faulty guest sends ATA commands to an ATAPI device (bug #6597)
Parallels: fixed deletion of the image during suspend, pause or power off (4.0 regression)
Bridged networking: fixed host kernel panic when bridging to devices with no TX queue (4.0 regression; Linux hosts only; bug #7908)
NAT: port-forwarding rule registration respects protocol parameter (bug #8094)
E1000: fixed PXE boot issues with WDS (bug #6330)
Virtio-net: fixed the issue with TX performance in some Linux guests
ICH9: fixed VM crash (software virtualization only; bug #7885)
VGA: fixed VESA screen issue (4.0 regression; bug #7986)
Shared Folders: fixed parameter parsing when creating symbolic links, fixes 32-bit/64-bit bitness issue (bug #818)
Main: fixed crash under rare circumstances due to an invalid logging string (4.0 regression)
Main: improve error information propagation for errors preventing a VM start
Main: fixed problems with snapshots and non-ASCII characters in machine paths (bug #8024)
Webservice: now listens to localhost by default as documented (bug #6067)
Settings: do not fail loading machine settings if removeable drive attachment (host drive or image) cannot be found; with 4.0 this is much more likely when machines are moved from one host to another
Settings: fixed issue that changing a snapshot name or description was not saved to machine XML
OVF/OVA: fixed import of files created by other OVF tools (bug #7983)
rdesktop-vrdp: fix a crash during USB device enumeration (bug #7981)
Linux hosts: fixed a crash during USB device enumeration.
Linux hosts: try a bit harder to allocate memory (bug #8035; 4.0 regression)
Guest Additions: fixed parsing of parameters for guest control in VBoxService (4.0 regression; bug #8010)
Windows Guest Additions: automatic logon on Windows Vista/Windows 7 now supports unlocking previously locked workstations