As a professional in the cyber security field, I’m often asked about the various threats that can potentially infiltrate a company’s network. One such threat is known as a VLAN hopping attack. This sneaky, yet dangerous tactic can catch even the most diligent of IT administrators off guard, leaving the network vulnerable to data breaches and other malicious activity.

Have you ever heard the phrase “divide and conquer”? That’s essentially what a VLAN hopping attack does. It takes advantage of the way that a network is divided into various VLANs, or Virtual Local Area Networks, and targets the weaknesses in the network’s infrastructure to gain access to sensitive data.

But why should you care about VLAN hopping? Well, imagine if your company’s confidential client information fell into the wrong hands. Or even worse, if your entire system was compromised and held for ransom. This is a reality that many businesses have faced due to VLAN hopping attacks.

In this article, we’ll explore the ins and outs of VLAN hopping attacks, how they work, and what you can do to prevent them from happening to your network. So buckle up and get ready to become an expert on network security threats.

What is a VLAN hopping attack?

What is a VLAN hopping attack?

How VLAN hopping works

VLAN hopping is a type of network security vulnerability where attackers exploit network protocols to penetrate VLANs (Virtual Local Area Networks), which are designed to improve network security. VLANs serve to separate network users and resources into different logical groups, restricting access to certain areas of the network. VLAN hopping happens when an attacker sends traffic into a switch port carrying traffic intended for a different VLAN. VLAN hopping attacks involve accessing and penetrating multiple VLANs within the same network instead of just one VLAN, which exposes more of the network to potential threats.

Exploiting this vulnerability involves using certain tactics to inject packets into the switch port, making the switch believe that the packets were addressed to it, and then forwarding the packets to other switch ports. This way, the attacker can gain unauthorized access to VLAN resources, such as sensitive data, and spread malware from one VLAN to another. VLAN hopping is often considered a security threat because it can lead to unauthorized access to sensitive information stored on VLANs.

Different types of VLAN hopping attacks

There are several different types of VLAN hopping attacks, including double tagging, switch spoofing, and VoIP (Voice over Internet Protocol) hopping.

Double tagging occurs when an attacker tags a packet with two VLAN IDs. This tricks the switch into thinking that the packet is meant for a particular VLAN, allowing the attacker to access the resources of another VLAN. Switch spoofing involves an attacker impersonating a switch, resulting in the switch forwarding packets to the attacker. VoIP hopping is a type of VLAN hopping that targets VoIP traffic which is usually carried in a separate VLAN. A VoIP hopping attacker can gain access to voice traffic by sending packets to a voice VLAN, then going to the data VLAN to which the VoIP phone is connected.

Examples of recent VLAN hopping attacks

One of the most well-known VLAN hopping attacks occurred in 2008 when the TippingPoint Zero Day Initiative discovered a vulnerability in the open-source VLAN trunking protocol. An attacker could send a specific packet to a target switch, which caused the switch to believe the packet originated from a VLAN it would not usually permit access to. This vulnerability could then be exploited for a VLAN hopping attack.

Another significant VLAN hopping incident occurred in 2019, where researchers uncovered a vulnerability in the Common Industrial Protocol (CIP), which could be exploited to allow attackers unauthorized access to critical networks. The vulnerability could allow attackers to bypass CIP Security, which is a protocol used by many industrial control system vendors to authenticate devices and protect an industrial network’s information.

Common techniques used to prevent VLAN hopping attacks

Preventing VLAN hopping attacks involves implementing several security measures to secure the network. One of the most effective ways of preventing VLAN hopping attacks is to establish and enforce port security at every switch port on the network. This way, any potential VLAN hopping attacker will be unable to connect to the network and send unauthorized traffic.

Another measure is disabling any unnecessary VLAN trunking protocols or setting them up securely. Native VLAN should be configured in a dedicated VLAN, and any unused ports should be shut down to prevent unauthorized access. Network administrators can also set up Access Control Lists (ACLs) to monitor all traffic, allowing them to detect and mitigate VLAN hopping attempts.

Employing proper VLAN configuration and monitoring techniques should also be prioritized to detect any abnormal activity. This helps in creating a security response plan to quickly contain and eliminate any attack.

How to detect a VLAN hopping attack

Detecting a VLAN hopping attack can be challenging, but some signs can indicate the presence of such an attack. Typically, when a VLAN hopping attack occurs, there is an increase in MAC addresses or changes to the ARP (Address Resolution Protocol) table. When this happens, network administrators should investigate and determine if there has been an unauthorized connection or if a VLAN hopping attack is in progress.

Using a Network Intrusion Detection System (NIDS) is also a possible way to detect VLAN hopping attacks and other security threats. NIDS analyzes network traffic and can identify suspicious activity, such as rogue packets or double-tagged packets. If any malicious traffic is detected, the NIDS will trigger an alert that the network administrators can investigate further.

The role of VLAN segmentation in preventing VLAN hopping

VLAN segmentation is one of the most critical concepts in network security since it can help prevent VLAN hopping attacks. It involves breaking up the network into different VLANs, allowing network administrators to regulate traffic flows and restrict access to different areas of the network. This segmentation is built around finalizing the infrastructure— every segment or VLAN should only contain resources and users with the same security level.

For instance, controlling resources that host sensitive data by placing them in their separate VLANs is an excellent strategy to secure access to the resources. VLAN segmentation operates a similar service to a jail or cell; once the attacker gains control of a VLAN, VLAN segmentation ensures that the attacker’s influence is limited.

Key takeaways for protecting against VLAN hopping attacks

To summarize, here are the crucial takeaways for protecting against VLAN hopping attacks:

• Enable port security at every switch port to prevent unauthorized access to the network;
• Use secure VLAN trunking protocols and disable any unnecessary protocols;
• Configure Native VLAN in its dedicated VLAN and shut down all unused switch ports;
• Implement Access Control Lists to monitor all traffic;
• Employ proper VLAN segmentation techniques;
• Detect VLAN hopping attacks by monitoring the ARP table and using NIDS;
• Stay connected with industry updates and security patches to keep the network secure.

In conclusion, VLAN hopping attacks remain a security concern that requires network administrators to be proactive and vigilant in their network security measures. By investing in the right security technologies and implementing best practices, organizations can prevent VLAN hopping attacks and secure their networks.