The Overlooked Problem of 'N-Day' Vulnerabilities

Security Researcher Joseph Pantoga contributed to this article.

Zero-day attacks tend to steal the spotlight when it comes to cybersecurity threats, but it is actually the known vulnerability — the "N-day" — that poses a much larger problem for many organizations and particularly those in the industrial sectors.

Whereas zero-days are a class of vulnerability that is unknown to a software developer or hardware manufacturer, an N-day is a flaw that is already publicly known but may or may not have a security patch available. There are countless known vulnerabilities in existence today, and many large commercial and governmental entities will find they have significant exposure within their broad network footprints.

However, the problem is far more acute for organizations that rely on industrial control systems (ICS) such as the energy, manufacturing, and infrastructure sectors. This is because ICS equipment can be extremely difficult to update and patch. To make matters worse, ICS firmware is often developed with insufficient built-in security controls, and product manufacturers can be slow to fix newly discovered vulnerabilities and threats.

For more than a year, our team analyzed unpatched N-day vulnerabilities in the firmware of widely used ICS devices in order to gain a better understanding of the problem. Some of these findings were recently presented at the S4x18 security conference in Miami. We found that N-days are extremely common in the ICS environment. Nearly all the operators who read this article are likely to have numerous N-days in their systems.

N-Days vs. Zero-Days
N-day vulnerabilities are a goldmine for attackers because the hard work has already been done. In certain cases, active exploits may already exist and be readily available from public disclosure documents. Compare this with zero-days, which are time-consuming and expensive to find and exploit — the reason why their use is declining among criminal groups.        .

While N-days pose a threat to any large network, industrial users are at an especially high risk because of specific circumstances unique to those environments:

Real-World Cases Illustrate the Risks
The industry has already seen a number of attacks on industrial targets that have exploited N-day vulnerabilities in ICS devices and protocols. Some examples include: 

High-Risk Vulnerabilities
Many of the N-days we discovered in ICS firmware are critical in nature and could allow a hacker to gain remote access and total control over parts of an industrial operator's network or facility. These N-days could allow attackers to replicate the effects of CrashOverride, TRITON, BlackEnergy, or even Stuxnet much more easily, and at a much wider scale.

For example, in our research into the VxWorks 5.5.1 vulnerability (discussed above), we found that every major manufacturer had a product that remains unpatched against this N-day. In no case was this vulnerability listed for the individual ICS products, so vendors may not even know these vulnerabilities exist. The vulnerabilities can be exploited for such malicious purposes as manipulating settings and controls, physically damaging or destroying equipment, disrupting key operations, and stealing sensitive information.

Due to the large number of vulnerabilities we discovered and the long lead time on ICS patching (as well as the low patch penetration rate), we decided not to disclose individual vulnerabilities against named devices for fear of arming attackers while device operators would be unable to respond.

Patching Is Not the Answer
ICS N-days are not an easy problem to fix. Solutions are limited by technical complications and a slow-to-act supply chain. Nonetheless, there is a lot the industry can do to address the problem.

To start, the current reactive approach of patching known vulnerabilities is no longer tenable. Every component of the ICS environment should have strong security baked into the software, firmware, and hardware from the very start in order to lower the overall risk of N-days and other problems, and to mitigate or prevent damage from their exploitation.

The best solutions will combine intrusion detection and mitigation techniques to protect against known and unknown attacks without relying on continuous updates. By and large, these features do not exist, so it is incumbent upon manufacturers to develop or source this technology as quickly as possible.

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