![]() Most switches will only remove the outer tag and forward the frame to all native VLAN ports. This attack takes advantage of how many switches process tags. ![]() Double Taggingĭouble tagging occurs when an attacker adds and modifies tags on an Ethernet frame to allow the sending of packets through any VLAN. If the target switch has one of those modes configured, the attacker then can generate a DTP message from their computer and a trunk link can be formed. This occurs when an interface is configured with either "dynamic desirable", "dynamic auto" or "trunk" mode. This exploit is only successful when the legitimate switch is configured to negotiate a trunk. Once the trunk link is established, the attacker then has access to traffic from any VLAN. As mentioned before, packets from any VLAN are allowed to pass through a trunking link. Switched Spoofing VLAN AttackĪn attacker acts as a switch in order to trick a legitimate switch into creating a trunking link between them. A trunk port can be configured manually or created dynamically using Dynamic Trunking Protocol (DTP).ĭTP is a Cisco proprietary protocol where one use is to dynamically establish a trunk link between two switches. Trunking ports allow for traffic from multiple VLANs. A trunking port is used when connecting two switches or a switch and a router together. ![]() With the implementation of VLANs, each access port is assigned to only one VLAN. An access port is typically used when connecting a host to a switch. On a switch, a port is either configured as an access port or a trunking port. We are not necessarily exploiting the device itself, but rather the protocols and configurations instructing how they operate. It is crucial we understand how switches operate if we would like to find and exploit their vulnerabilities. I will then discuss mitigation techniques. In this article, I will go through the two primary methods of VLAN hopping, known as 'switched spoofing', and 'double tagging'. However, many networks either have poor VLAN implementation or have misconfigurations which will allow for attackers to perform said exploit. With proper switch port configuration, an attacker would have to go through a router and any other layer 3 devices to access their target. This type of exploit allows an attacker to bypass any layer 2 restrictions built to divide hosts. Learn more about network segmentation and VLANs here. However, with an exploit known as 'VLAN Hopping', an attacker is able to bypass these security implementations. Security is one of the many reasons network administrators configure VLANs. Any packets sent between VLANs must go through a router or other layer 3 devices. For example, a host on VLAN 1 is separated from any host on VLAN 2. A virtual local area network (VLAN) is used to share the physical network while creating virtual segmentations to divide specific groups.
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