Industrial Cybersecurity

The Human Attack Surface: The Weakest Link in Your ICS Security

Jeff Lund

Like many specialized disciplines, the world of cyber security is filled with technical jargon that can hamper communication. In this blog, we’ll demystify some cyber security best practices and terms, as we focus on an often-overlooked factor in ICS and corporate security known as the “attack surface.” We’ll take an in-depth look at what attack surfaces are, how to keep them safe and how the human element plays a critical role in their security.

Like many specialized disciplines, the world of cyber security is filled with technical jargon that can hamper communication. In this blog, we’ll demystify some cyber security best practices and terms, as we focus on an often-overlooked factor in ICS and corporate security known as the “attack surface.” We’ll take an in-depth look at what attack surfaces are, how to keep them safe and how the human element plays a critical role in their security.

What is the Attack Surface? 

The term “attack surface” is security jargon for the sum of your security risk exposure. It is the aggregate of all known, unknown, reachable and potentially exploitable weaknesses and vulnerabilities across an organization.


All organizations, regardless of industry, have an attack surface. However, for those who manage energy, utility and other critical infrastructure sites in today’s highly interconnected world, this concept is especially critical to review. Awareness of weaknesses, prioritization of risk and layered defenses can reduce the attack surface and limit disruption, enhance predictable operations and lower business risk. 


The attack surface and how to defend it is not a new concept. Broadly oversimplified, the industrial attack surfaces that need defending include (but are not limited to) the following areas: 

  • Physical and virtualized assets
  • Hardware
  • Firmware
  • Software
  • Databases
  • Networks (including industrial communications protocols, serial links, remote access, networking devices, firewalls)
  • Physical facilities
  • Personnel

The Human Element of Attack Surfaces 

Out of the list of attack surfaces listed above, one stands out from the rest: Personnel. This is because securing the “human element” is easy to overlook when assessing vulnerable attack surfaces within your network. Simply defined, the human attack surface is the sum of all exploitable security holes or gaps created by humans within your ICS operations environment. Human behaviors in ICS realms are no different than within many professional settings. As human beings, we make mistakes and are prone to error. However, in ICS and corporate security settings, errors or negligence can have serious physical consequences, even with safety systems in place.


When considering human factors that can influence the size of your attack surface and, by doing so, put your business at risk, here are a few of the most common personnel shortcomings:

  1. Lack of ICS security knowledge – Personnel lacking the appropriate level of ICS security knowledge are more prone to make mistakes. For example, employees or contractors might be charging cell phones or other mobile devices on ICS USB ports, exposing sensitive data belonging to both the company and the employee. 

  2. Resistance to change (or choosing to bypass security rules/policies to avert disruption) – Periodically troubleshooting or “taking care of things” by modifying or updating firmware or asset configurations without letting others know, or doing email on engineering workstations that also have access to HMI consoles are examples of employees knowing the right thing to do but taking the route that causes less friction for themselves and others.

  3. Susceptibility to social engineering – Social engineering involves attackers appealing to your personnel’s human nature. It’s centered around creating a sense of urgency that pressures people into making risky decisions, or appealing to a person’s innate desire to help others. Social engineering attacks can be as simple as attackers following someone to an employee-only entrance and asking the employee to hold the door because they forgot their ID badge at home. 

  4. Opportunities for operator error or negligence – As the old saying goes, “To err is human.” Your personnel are bound to make mistakes from time to time. While some mistakes are more easily corrected, some carry serious consequences when put into the context of ICS security. One such example would be sharing the WiFi password for the break room with visiting family members so they can connect personal devices. Or perhaps you’ve forgotten to disable network access for former employees and contractors. Both expose your network to a whole host of external threats.

  5. Awareness training for email security – Email security protocols should be a top priority. According to the Q2 2017 malware review and research report by email-filtering company Phishme, more than 90 percent of all malware (including ransomware) targets our inboxes. 

  6. Lack of ICS security policies or training, etc. – Providing employees with security guidelines and conducting regular training and remediation sessions will keep personnel sharp and alert to security risks. For example, personnel should be aware of both safe and unsafe connections through which they can access plant networks and resources. Logging in at your workstation and jumping on the local Starbucks WiFi are two very different things.

Practical Starting Points to Reduce Your Human Attack Surface 

If you’d like to begin to scope and reduce your human attack surface, here are a few primary focus areas that can help make the biggest improvement:


1. Know Who Has Physical and Cyber Access 

  • The Problem: Many people are given access to your physical and cyber assets. This is a broader group than just employees. It can include contractors, maintenance and facility workers, industrial equipment manufacturers, system integrators, consultants, supply chain partners, etc. In many cases, the access is supposed to be temporary but never gets revoked.

  • The Solution: Establish and enforce procedures to limit or discontinue physical and cyber access for specific employees and non-employees. This will involve participation of the IT team, human resources and likely those who monitor physical access.

2. Securing Email and Training Personnel 

  • The Problem: Phishing and spear phishing are among the most common ways to infect systems for a whole array of purposes – from locking users out of their systems to stealing login and password credentials to gaining access to critical assets such as HMI or PLCs and potentially causing disruption or harm. 

  • The Solution: Consider acquisition of technology to help filter out suspicious emails and train your personnel on secure email practices (if email is allowed within your ICS environments). In a bigger effort, you would consider a full ICS security program with email security awareness as one of many important components.


3. Social Engineering Awareness Training 

  • The Problem: Social engineering has become so common and successful that it deserves its own category of attack surface. Social engineering relies heavily on human interaction and often involves tricking people into breaking normal security procedures, giving up personally identifying information or corporate details.

    Popular social engineering techniques rely on a person’s willingness to be helpful or their lack of attention to detail when in a hurry (like not noticing a slightly misspelled URL or website that could indicate malicious intent). These messages often have a tone of urgency that can cause recipients to miss obvious clues. For example, an attacker might pretend to be a co-worker who has some kind of urgent problem that requires access to additional network resources.

    There are many variants of social engineering that also involve social media such as Facebook, Twitter and LinkedIn and even text messages sent via cell phones. After research and possibly a few phone calls, social engineers could craft effective spear phishing emails, causing C-suite, privileged users and field technicians to fall prey. 
  • The Solution: Reducing the social engineering attack surface will require educating employees about typical techniques and how to recognize them. This facet of the human attack surface is constantly changing and will require monitoring for trends that may apply to your industry, locale or employee type. This information can help employees recognize interactions that could lead to compromise, disruption and operations downtime.

In Conclusion

One of the great strengths of highly secure organizations is their emphasis on communicating security awareness, cyber-physical risks and safety principles to their employees, partners, supply chain and even their customers (as when using the web to gain secure access to pay their utility bill.)


How secure is your ICS security program? Which of your attack surfaces are currently the most vulnerable? Let’s discuss more ways you can secure your energy, utility or critical infrastructure networks.