Phantom Tap (PhanTap) – An ‘Invisible’ Network Tap Aimed at Red Teams.
With limited physical access to a target building, this tap can be installed inline between a network device and the corporate network.
PhanTap is silent in the network and does not affect the victim’s traffic, even in networks having NAC (Network Access Control 802.1X – 2004). PhanTap will analyze traffic on the network and mask its traffic as the victim device.
It can mount a tunnel back to a remote server, giving the user a foothold in the network for further analysis and pivoting. PhanTap is an OpenWrt package and should be compatible with any device. The physical device used for our testing is currently a small, inexpensive router, the GL.iNet GL-AR150.
- Transparent network bridge.
- Silent : No ARP, multicast, broadcast.
- 802.1x passthrough.
- Automatic configuration:
Capture traffic exiting the network (the destination is non RFC1918), source IP and MAC is our victim, destination MAC is our gateway,
SNAT bridge traffic to the victim MAC and IP address,
set the router default gateway to the MAC of the gateway detected just before.
- Introspects ARP, multicast and broadcast traffic and adds a route to the machine IP address and adds the machine MAC address to the neighbor list, hence giving the possibility of talking to all the machines in the local network.
- Learns the DNS server from traffic and modifies the one on the router so that it’s the same.
- Can run commands (ex: /etc/init.d/openvpn restart) when a new IP or DNS is configured.
- Lets you choose any VPN software, for example OpenVPN tcp port 443 so it goes through most firewalls.
- You can talk to the victim machine (using the gateway IP).
PhanTap has been tested with the GL.iNet GL-AR150. This device has two separate network interfaces in OpenWrt (eth0, eth1).
If your device is using an internal switch (swconfig based) with interfaces like eth0.1, eth0.2, some special traffic might be blocked, e.g. 802.1Q (tagged vlan), but PhanTap should work.
- Install a snapshot build, for the GL.iNet GL-AR150
- Update the OpenWrt package list
opkg install phantap phantap-learn
- Configure the Wifi and start administering the router through it.
- Either reboot the device, or run /etc/init.d/phantap setup.
- Get the interface names from that device:
# uci show network | grep ifname
In this example we are using a GL-AR150, which only has 2 interfaces.
Add the interfaces to the phantap bridge via the following commands in the cli (assuming we are using a GL-AR150):
- uci delete network.lan.ifname
- uci delete network.wan.ifname
- uci delete network.wan6.ifname
- uci set network.phantap.ifname=’eth0 eth1′
- uci commit network
- /etc/init.d/network reload
Phantap is now configured, as soon as you plug it between a victim and their switch, it will automatically configure the router and give it Internet access.
You can add your favorite VPN to have a remote connection back. Tested PhanTap with Vpn, port TCP 443, to avoid some detection methods.
You can also add a command to be ran when a new IP or DNS is configured, in /etc/config/phantap, e.g. /etc/init.d/openvpn restart (restart VPN service).
You can also look at disabling the wifi by default and using hardware buttons to start it (https://openwrt.org/docs/guide-user/hardware/hardware.button).
Limitations or how it can be detected :
- The GL.iNet GL-AR150 and most inexpensive devices only support 100Mbps, meanwhile modern network traffic will be 1Gbps.
- The network port will stay up, switch side, when the victim device is disconnected/shutdown.
- There is no re-configuration of PhanTap, so we might use an IP that has been reattributed to another device (roadmap DHCP).
- Some traffic is blocked by the Linux bridge (STP/Pause frames/LACP).
- Add logic to restart the detection when the links go up/down.
- Add DHCP packet analysis for dynamic reconfiguration.
- Add IPv6 support.
- Test limitations of devices that have switches(swconfig) instead of separate interfaces.