Securing a wireless application

Industrial wireless applications are seeing more and more action by leading manufacturers and operators to improve availability and reduce costs. In theory, that sounds great, but it is worth considering how difficult it is to make sure these industrial networks are secure before using them in a facility.

The good news is the best practices, technologies, and products currently available make implementing wireless applications securely straightforward for engineering teams. Wireless applications are no different than wired applications when it comes to an essential industrial control system (ICS) security best practice-defense-in-depth (DiD). DiD is a holistic approach built on three core concepts:

1. Multiple layers of defense: A variety of security solutions end up used so if an attacker bypasses one area, another can provide the needed defense.
2. Differentiated layers of defense: Each security layer is slightly different so an attacker can′t automatically get through all layers of defense.
3. Threat-specific layers of defense: Each defense is for the specific context and threat, allowing protection based on the behavior and context of the systems using these protocols.

Whether a threat is an accidental internal incident or a deliberate external attack, a DiD approach will detect, isolate, and control it. The wireless defense strategies outlined work together to provide the layers of protection needed to make sure the user’s wireless local area network (WLAN) is secure.

Protection technique #1

A challenge with WLAN transmission paths is they can broadcast outside a company’s property boundaries. Thus attackers don′t need direct, physical access to an industrial network in order to interfere with its operation and capture critical and confidential information.

Industry cooperation has led to standards such as IEEE 802.11i/WPA2 that protect the confidentiality and integrity of wireless data. All current products on the market must comply with these standards, ensuring control system communications are authentic, and attackers cannot extract sensitive data.

In regard to WPA2, be sure to implement its Enterprise mode for strong device authentication. Unlike personal networks, WPA2 (Enterprise mode) provides different keys for different devices, with the keys managed in a central database such as RADIUS. Lost or stolen devices can be disconnected from the network simply by removing their information from the database.

Furthermore, with WPA2 (Enterprise mode), individual devices can be assigned to different virtual LANs (VLANs) so devices with different roles can be clearly differentiated. This segmentation makes it difficult for an attacker to gain further access to a network should a single device be compromised—an example of DiD. 

Protection technique #2

Another aspect of wireless communications you want to protect are management frames. These are network packets that organize the internal operation of the network, and they are exceptionally vulnerable to forgery and wiretapping.

Devices use management frames to log on and off the network, initiate new key exchanges, and report when they roam from one access point to another. Information can be captured from wiretapped management frames, and forged management frames can be sent out with a wrong sender identity. An attacker can disrupt the operation of the network by disconnecting a victim device from the network.

Protected management frames (PMF) are useful because they are designed to protect against forgery by extending the mechanism for authentication and encryption present in WPA2 to management frames. By using products with the PMF capability, it is impossible for misused management functions to attack a network. 

Protection technique #3

Even the most effective WLAN encryption doesn’t offer protection when a security incident originates inside the network. But, by selectively limiting communication to only what is required to run the industrial application, additional barriers are established that are designed to limit the impact of internal attacks.

This type of limitation is another defense-in-depth mechanism that considerably increases the all-around security of a network. Other strategies for limiting communication within the network include:

• Protect WLAN data by implementing a configurable Layer 2 firewall at the Ethernet level. To do this you need to make sure you are using Access Points with a built-in Layer 2 firewall. The best ones can filter routed and bridged traffic as well as packet-filter traffic between WLAN clients.
• Apply stateful deep-packet inspection (DPI) to secure protocols. After the Layer 2 firewall rules are applied, the DPI firewall inspects the content of the contained messages and applies more detailed rules. For example, a Modbus DPI firewall can determine if the Modbus message is a read or a write message and then drop all write messages. Good DPI firewalls can also "sanity check" traffic for strangely formatted messages or unusual behaviors.

DPI firewalls are often used to protect zones of equipment with similar security requirements as per ISA IEC 62443 or to protect equipment critical to the process. Be aware that DPI is sometimes known by other terms, such as content inspection or protocol whitelisting, and it is not a widely available capability.

Key strategy

Industrial wireless benefits such as improved uptime, reduced costs, and faster and more accurate data collection are readily achievable today using the techniques described. Protecting data, devices, and the control network is possible using the techniques described in this article.

– Heather MacKenzie is with Tofino Security, a Belden company. This content originally appeared on ISSSource. Edited by Chris Vavra, production editor, CFE Media, cvavra@cfemedia.com.

Original content can be found at www.isssource.com.

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