tunnel virtualbox through socks (using poor man's vpn = ssh socks tunnel)

tunnel_vm_socks.txt

# ssh socks server on :5000 (tunnels traffic to tunnel-endpoint-server)
ssh -D5000 -NT -v user@tunnel-endpoint-server

# redsocks: https://github.com/darkk/redsocks 
# 1.) as a socks client, listen on :4999 and connect to :5000
# 2.) run a dummy udp dns server on :5300 (to force vm to fallback to tcp which is working through ssh socks) 
cat > redsocks.conf <<EOF
base { log_info=on; redirector=iptables; }
redsocks { local_ip=127.0.0.1; local_port=4999; ip=127.0.0.1; port=5000; type=socks4; }
dnstc { local_ip=127.0.0.1; local_port=5300; }
EOF
redsocks -c redsocks.conf

# run virtualbox vm with host-only interface (e.g. vboxnet0 as 192.168.56.1/24)
# dhcp is ok, but setting proper dns ip (behind tunnel-endpoint-server) is mandatory

# redirect virtualbox traffic from vboxnet0 to socks client :4999
# and redirect udp dns to dummy service
sysctl -w net.ipv4.conf.vboxnet0.route_localnet=1
iptables -t nat -F PREROUTING
iptables -t nat -A PREROUTING -i vboxnet0 -s 192.168.56.0/24 -p tcp -j DNAT --to-destination 127.0.0.1:4999
iptables -t nat -A PREROUTING -i vboxnet0 -s 192.168.56.0/24 -p udp --dport 53 -j DNAT --to-destination 127.0.0.1:5300

# alternative iptables rules if we want to route host localnet (e.g. 192.168.1.0/24) directly
iptables -t nat -F PREROUTING
iptables -t nat -A PREROUTING -i vboxnet0 -s 192.168.56.0/24 -p tcp ! -d 192.168.1.0/24 -j DNAT --to-destination 127.0.0.1:4999
iptables -t nat -A PREROUTING -i vboxnet0 -s 192.168.56.0/24 -p udp --dport 53 -j DNAT --to-destination 127.0.0.1:5300
iptables -t nat -A POSTROUTING -s 192.168.56.0/24 -p tcp -d 192.168.1.0/24 -j MASQUERADE