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

- GUI: the USB filter settings dialog should allow to specify the USB revision in hexadecimal format (bug #15400)
- GUI: fixed crash on certain hosts when pressing certain key combinations (Windows hosts only; bug #15719)
- GUI: fixed issue with updating the available-geometry on host-screen work-area resize
- GUI: don't crash / hang on certain environments if accessibility support is enabled
- GUI: fixed various issues in Unscaled HiDPI Output mode (bug #15707)
- GUI: extend the VM Input menu with Print Screen-related actions
- GUI: improved handling of inserting the Guest Additions ISO image by trying all available optical drives rather than only the first one and by not asking the user if he wants to force unmounting (which doesn't work in most cases anyway)
- API: default to RTC using UTC for Solaris 11 guests
- Settings: be less restrictive when reading a VM configuration containing a host-only adapter without an interface name
- Storage: fixed resizing VDI images resulting in an unbootable image under certain circumstances (bug #15983)
- NAT: fixed several 5.1.8 regressions on Mac OS X and Windows hosts (bug #16084)
- Audio: fixed a few 5.1.x regressions by using the audio code from 5.0.x until the audio overhaul is completed
- VBoxManage: fixed documentation of the storagectl command (bug #15971)
- Build system: another fix for building VirtualBox on systems which default to Python 3
- Windows hosts: hardening fix for Windows 10 build 14971 (bug #16202)
- Windows Additions: properly start the VirtualBox guest services even if the guest user name contains special characters (bug #15982)
- Solaris Additions: fixed preemptible mouse notification callback being executed under a spinlock for Solaris guests
- Linux hosts / guests: Linux 4.9 fixes (bugs #16155 and #16064)
- Linux Additions: fixed Linux kernel module override rule (thanks Mark Furneaux)