What attack technique uses double VLAN tagging to access network devices that might not otherwise be accessible?
- VLAN hopping
- DHCP spoofing
- Rogue devices
- MAC flooding
Double VLAN tagging is used by a VLAN hopping attack. An attacker can create a packet with two VLAN headers on it and send it to a switch. The switch port will strip off the first header and leave the second. The second header will be seen as the originating VLAN, allowing the attacker access to a VLAN they are not connected to. This becomes a security concern because this hopping can be accomplished without passing through a router and its security access lists. For this reason, private VLANs and VACLs should be used to secure access between VLANs.
DHCP spoofing is an attack that can be used to force user traffic through an attacking device. This is accomplished by an attacker responding to DHCP queries from users. Eliminating the response from the correct DHCP server would make this more effective, but if the attacker’s response gets to the client first, the client will accept it. The DHCP response from the attacker will include a different gateway or DNS server address. If they define a different gateway, the user traffic will be forced to travel through a device controlled by the attacker. This will allow the attacker to capture traffic and gain company information. If the attacker changes the DNS server in the response, they can use their own DNS server to force traffic to selected hosts to go to a device they control. Again, this would allow the attacker to capture traffic and gain information.
MAC flooding is an attack technique that attempts to fill a switch’s MAC address table so the attacker can capture flooded traffic sent from the switch. The concept of this attack is to use the CAM table limit to the attacker’s advantage. The attacker would send packets addressed from a large number of MAC addresses to the switch. The switch adds the source MAC address to the MAC address table. Eventually no more MAC addresses can be added because the table is full. When this occurs, any packets destined for a MAC address not in the table will be flooded to all other ports. This would allow the attacker to see the flooded traffic and capture information. The switch would be essentially functioning as a hub in this case.
A rogue device is a device attached to the network that is not under the control of the organization. This term is normally used to mean a wireless device, perhaps an access point that is not operating as a part of the company’s infrastructure. Employees may bring their own access points and connect them to the network so they can use their computer wirelessly. This creates a security gap since the device is probably not secured to protect the traffic. An attacker could connect a rogue access point to a company’s network and capture traffic from outside the company’s premises.
Configure and verify switch security features