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One of the staples of network defense is blocking traffic to and from a list of "known bad" sites on the Internet. However, few organizations are in a position to produce such a list themselves, so pragmatically this approach depends on the existence of third-party "threat intelligence" providers who specialize in distributing feeds of unwelcome IP addresses. However, the choice to use such a strategy, let alone which data feeds are trusted for this purpose, is rarely made public and thus little is understood about the deployment of these techniques in the wild. To explore this issue, we have designed and implemented a technique to infer proactive traffic blocking on a remote host and, through a series of measurements, to associate that blocking with the use of particular IP blocklists. In a pilot study of 220K US hosts, we find as many as one fourth of the hosts appear to blocklist based on some source of threat intelligence data, and about 2% use one of the 9 particular third-party blocklists that we evaluated. 

The term "threat intelligence" has swiftly become a staple buzzword in the computer security industry. The entirely reasonable premise is that, by compiling up-to-date information about known threats (i.e., IP addresses, domain names, file hashes, etc.), recipients of such information may be able to better defend their systems from future attacks. Thus, today a wide array of public and commercial sources distribute threat intelligence data feeds to support this purpose. However, our understanding of this data, its characterization and the extent to which it can meaningfully support its intended uses, is still quite limited. In this paper, we address these gaps by formally defining a set of metrics for characterizing threat intelligence data feeds and using these measures to systematically characterize a broad range of public and commercial sources. Further, we ground our quantitative assessments using external measurements to qualitatively investigate issues of coverage and accuracy. Unfortunately, our measurement results suggest that there are significant limitations and challenges in using existing threat intelligence data for its purported goals.