PVLAN and VACL, Powerful Tools for Attack Surface Reduction.

Despite deploying multi-layered security controls and cutting-edge solutions, our infrastructure remains vulnerable to attacks. This vulnerability could potentially be exploited through zero-day threats, providing initial access to adversaries. The reality is that even with vast investments in premium security controls and network detection mechanisms, we remain exposed to cyber threats.

This article does not intend to deeply probe strategies for reducing the attack surface. Instead, it seeks to highlight a frequently overlooked control mechanism nestled within Layer 2 or the switching layer. This underestimated mechanism, although often disregarded, forms a critical part of our defence strategy.

Once threat actor gain initial access, they typically engage in a discovery process, seeking to move laterally across the network. The ultimate objective of these threat actors is to gain access to valuable data and assets, the nature of which hinges on their specific motives for the breach. The various measures we deploy across multiple layers, such as NIPS, EDR, Firewalls, XDR, so on, are primarily designed to manage and mitigate the attack surface.

The stages of Discovery and Lateral Movement in cyber attacks underscore the significance of solutions like micro-segmentation. Micro-segmentation excels in further narrowing the attack surface, effectively shrinking the ‘circumference’ of potential vulnerabilities that could be exploited by attackers. This approach strengthen overall network security, creating a complex terrain that is harder for cybercriminals to penetrate. Therefore, the integration of micro-segmentation into our defensive strategies cannot be overstated.

While it might be tempting to believe that such strategies would necessitate infrastructure upgrades, and investments. It’s crucial to consider the existing features offered by various other layers, such as Private VLANs (PVLANs) and #vlan Access Maps, both of which are Layer 2 capabilities. These mechanisms can achieve something akin to #microsegmentation #networksegmentation . The fundamental requirement is to limit hosts communication within the same network from interacting with each other and to allow them to communicate solely with network gateways, probably a firewall, or the permissible resources in the routed domain. By leveraging such simple and proven capabilities, we can significantly obstruct the lateral movement and discovery efforts of malicious actors, thereby improving?overall network security posture. this best work when used in combination with VLAN ACLS which can even control traffic to a routed domain.

Now, let’s delve into the specifics of Private VLANs and VLAN Access Control.

• Private VLAN (PVLAN) is an advanced network segregation tool that provides high-level network isolation at the subnet level. It inhibits hosts on the same network segment from directly communicating with each other, thereby strengthening security. Essentially, it enables micro-segmentation within a single VLAN, controlling host communication and restricting it to interactions with designated gateways or servers. This proves particularly beneficial in mitigating lateral movement and thwarting discovery attempts by threat actors within the network.
• VLAN Access Control Lists (VACLs), also known as VLAN Access Maps, are another powerful security feature. They permit finer control over network traffic within a VLAN by applying policies for permitted and denied traffic. Unlike regular Access Control Lists (ACLs) that filter traffic moving between VLANs, VACLs can filter traffic within the same VLAN. This adds an additional layer of security, providing granular control over internal traffic and thereby minimising the potential for internal network exploits.

Before I conclude, let's consider an example. Consider a scenario where a network consists of 100 physical hosts. In this case, an attacker successfully gains initial access through a phishing attack intended for spreading ransomware. During the discovery phase, adversaries can use a techniques to gain insight of the other connected nodes. A simple arp -a command can give insight of other nodes in same network. However, if the endpoints are segregated within a private VLAN on isolated ports, the initial access foothold would not provide the attacker with access to such extensive information. Instead, they would likely only have visibility of the gateway, greatly reducing the threat surface and effectively limiting the potential impact of the attack.

In conclusion, it is clear that while sophisticated and costly security solutions are essential, they are not the sole components in ensuring comprehensive cybersecurity. There is great value in revisiting and leveraging foundational network tools, such as those found in Layer 2 or the switching layer. Underutilised features like Private VLANs and VLAN Access Maps are powerful mechanisms that can significantly improve our cybersecurity posture. It’s important to assess the existing capabilities of your network infrastructure and leverage them to achieve segmentation objectives before considering additional investments or upgrades while building a resilient cybersecurity strategy.