VirtualBox crashes immediately after starting, when:

- Wifi is enabled on the host machine

- Wifi is connected to a public network with a captive (http redirect)
  authentication portal -- the kind that displays the auth page when you
  attempt to browse to http://www.google.com , for example.

- Automatic "check for updates" is enabled in VirtualBox.

Workarounds:

Disable automatic updates in VirtualBox. This is the recommended solution, as
these crashes indicate that VirtualBox is using unsecured HTTP to communicate
with the update server, and attempts to parse the substituted (captive
authentication) page instead. It may be possible to compromise VirtualBox using
injected HTTP traffic on a malicious access point.

Turn off wifi when starting VirtualBox, then turn it on once VirtualBox has
started.

Do the authentication before starting VirtualBox.