Tuesday, August 29, 2017

ICS-CERT Publishes 2016 Vulnerabilities Review

Yesterday the DHS ICS-CERT published their 2016 Annual Vulnerability Coordination Report. This is the second such report from ICS-CERT and many of the same problems exist in this year’s report. Additionally, ICS-CERT further complicates their reporting by making changes to the way they are ‘counting tickets’ in the report so that numbers are not directly comparable to previous years. Oh, yes, they are also reporting both FY 2016 and CY 2016 data, just to throw another monkey wrench into the data analysis comparison problem.

Changes in Data Reporting

The change in the way that ICS-CERT counted tickets makes a fundamental change in the data reported. ICS-CERT explains the change:

The method used to collect and report vulnerability data changed in 2016 from that used in prior years. In 2016, ICS-CERT began reporting metrics data on vulnerability tickets closed within the FY or CY accounting periods. This prevents reported metrics changing based on work accomplished throughout the life of an open ticket. In previous year’s reporting methods, actions taken prior to ticket closure could result in additional follow-on work being required, which in turn could change the reported metrics. It is therefore important to note that some information reported in published alerts and advisories in 2016 may not be included in the FY or CY data cited herein, since the associated vulnerability ticket may still be open. Data for tickets will be included in the reporting period in which the ticket is closed.

While the change in data accounting is a legitimate attempt to make the numbers more meaningful in the long run, it does make 2016 data to the same data from earlier years. This report makes that clear at multiple points in the discussion, but they continue to provide graphics comparing the numbers all the way back to 2010. I predict that a number of agencies and organizations will not make the distinction clear when they report on ICS-CERT vulnerability data.

Two Reports Make a Difference

Figure 3 in this year’s report shows how changes in vulnerability detection may be making major changes in how future reports may look. The final two columns in the table report 2016 data including a “2 ticket anomally”. The report explains these two tickets this way:

“The increase is primarily associated with two (2) tickets closed in 2016 that contain 1,418 and 460 vulnerabilities. Because these 1,878 validated vulnerabilities were associated with a small subset of affected products, there is some concern that these outliers could bias the metrics associated with vulnerability type and Common Vulnerability Scoring System (CVSS) scores. As a result, these are included in the total number of vulnerabilities reported to ICS-CERT; however, this data is not included in other metrics treated throughout this document.”

The two advisories are not named. They were a medical system advisory for a product from CareFusion and another from Philips Medical. Lest one thinks that this is just a medical device issue, there have been two similar large-vulnerability-number advisories already published this year for control system products from Rockwell (62) and Schneider (365). In each case the vulnerabilities come from third-party software or libraries included in the control system product.

ICS-CERT reports that these types of large-scale vulnerability detections have been made possible “by using automated scanning tools”. It would seem that the use of such tools will become more widespread and will almost certainly become a prime tool for researchers working for organizations with criminal or nefarious intent. This is of particular concern since many of these identified vulnerabilities are very old (in cyber years) and many have well known exploits available.

CWE-CVSS Analysis

This year’s report takes a completely different tack in looking at the variety of vulnerabilities reported. Last year much use was made of pie charts and word descriptions of the vulnerabilities. This year ICS-CERT goes to a more formal use of Common Weakness Enumeration (CWE) numbers and replaces multiple pages of pie charts with a single histogram showing the most frequent CWE numbers reported.

ICS-CERT has, instead of giving us greater detail on the types of vulnerabilities, provided more detail on the effectiveness of those vulnerabilities via a look at a compilation of the Common Vulnerability Scoring System (CVSS) data on those vulnerabilities. This includes a table of impact score results and a histogram for access vector analysis.

What is interesting in the impact scoring table is that the NIST CVSS impact categories are not equal size portions of the 10.0 scale used. The ‘critical’ category, for instance, is only one unit wide, while the ‘low’ category is four units wide, while the ‘medium’ and ‘high’ categories are three and two units wide respectively. Thus, if we were to see a random distribution of CVSS impact scores, we would expect to see a disproportionate share in the two lower categories. Instead what we see in the report’s Table 4 is a concentration in the two smaller categories at the dangerous side of the spectrum. This is further reflected in the table’s reported ‘CVSS Statistics’; an average value of 7.8 and a mean value of 7.5. Unfortunately, ICS-CERT again fails to provide a key statistic, the standard deviation, that provides more depth to the statistics reported.

Rating the Report

ICS-CERT has a mixed history with its wide variety of annual reports that it produces. I have very little use for many of the reports that they produce because of their lack of internally consistent definitions and misleading data. This report is fortunately better than average for ICS-CERT. The information is useful for its summary of the types of vulnerability reports that ICS-CERT produced over the year in question and the limited details available from those reports.

Unfortunately, ICS-CERT is still guilty of publishing four-color glossy corporate reports that do more to confuse than to clarify. The unexplained combining of fiscal year and calendar year reporting provides no new insights into the process. The changing of definitions of what constitutes a reportable ticket makes analysis of year-to-year trends questionable, but these trends will inevitably be carefully misreported in the press and abused by politicians and activists.

I did like the addition of a start to look at the numerical data found in CVSS data. More of that should be included in next year’s report. Unfortunately, reporting that data is going to have to include some sort of statement about the consistency of that data. While the CVSS system is an attempt to provide repeatable information about vulnerabilities, it is not a physical measure. This means that there is some bias in that data, depending on who scores the vulnerability. If ICS-CERT is providing the individual scores used in the system, that bias is at least somewhat consistent. If vendors are the source of the scoring, the bias will be much less structured. The data source needs to be disclosed.

In any case, I do recommend that those with an interest in the security of industrial control systems should read this report. Just be careful on how you use the inconsistent data.

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