Cisco AnyConnect VPN modifies/removes routes to the bridged network adapter on a VirtualBox VM when you log in. To connect to the VM again, you need to log off the VPN, as the Cisco VPN has a watchdog that reverts any route changes while the VPN is active. After logging off, run this reroute script:
#!/bin/bash
guestip="192.168.58.3"
guestmac="8:0:27:35:55:1d"
# The following 2 deletions are not always needed
# route -n delete ${guestip%.*}.0
# route -n delete $guestip/32
route -n add $guestip/32 -interface vboxnet0
arp -s $guestip $guestmac
netstat -rnf inet | grep 192