Linux – No USB devices available in VirtualBox

Oracle VirtualBox is unable to list/filter the USB devices attached to my system. As a result, the guest OS is not able to see any USB device either.

This is my configuration:

• Host: VirtualBox 5.0.0 r101573 on Ubuntu 14.04, with Oracle VM
  VirtualBox Extension Pack installed
• Guest: Windows 7, with VirtualBox Guest Additions installed

I've been trying with a USB flash drive and a Garmin sports watch: when connected to the host, they are both recognised by the system, i.e. they are in the list outputted by the lsusb command.

However, when running VirtualBox, no USB device is actually detected (Enable USB Controller is obviously checked). If I select the VM, then Settings -> USB and I try to add a filter, a tooltip is displayed:

<no devices available>

I've tried different options as USB controller, even tried to attach the
devices to different USB ports (2.0 instead of 3.0), but that didn't change
anything. Since no USB devices are listed there I assume the problem is with the host, not with the guest.

The USB mouse I have is working in both the host and the guest, but that's probably a device that is treated differently.

The VBox.log does not report anything suspicious regarding the USB, and VirtualBox does not throw any error either.

The same problem occurred when I had VirtualBox 4.3.30 installed.

Is there a way to resolve the issue?