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MITRE ATT&CK is an open-source taxonomy of adversary tactics, techniques, and procedures based on real-world observations. Increasingly, organizations leverage ATT&CK technique "coverage" as the basis for evaluating their security posture, while Endpoint Detection and Response (EDR) and Security Indicator and Event Management (SIEM) products integrate ATT&CK into their design as well as marketing. However, the extent to which ATT&CK coverage is suitable to serve as a security metric remains unclear— Does ATT&CK coverage vary meaningfully across different products? Is it possible to achieve total coverage of ATT&CK? Do endpoint products that detect the same attack behaviors even claim to cover the same ATT&CK techniques? In this work, we attempt to answer these questions by conducting a comprehensive (and, to our knowledge, the first) analysis of endpoint detection products' use of MITRE ATT&CK. We begin by evaluating 3 ATT&CK-annotated detection rulesets from major commercial providers (Carbon Black, Splunk, Elastic) and a crowdsourced ruleset (Sigma) to identify commonalities and underutilized regions of the ATT&CK matrix. We continue by performing a qualitative analysis of unimplemented ATT&CK techniques to determine their feasibility as detection rules. Finally, we perform a consistency analysis of ATT&CK labeling by examining 37 specific threat entities for which at least 2 products include specific detection rules. Combined, our findings highlight the limitations of overdepending on ATT&CK coverage when evaluating security posture; most notably, many techniques are unrealizable as detection rules, and coverage of an ATT&CK technique does not consistently imply coverage of the same real-world threats. 

Endpoint threat detection research hinges on the availability of worthwhile evaluation benchmarks, but experimenters' understanding of the contents of benchmark datasets is often limited. Typically, attention is only paid to the realism of attack behaviors, which comprises only a small percentage of the audit logs in the dataset, while other characteristics of the data are inscrutable and unknown. We propose a new set of questions for what to talk about when we talk about logs (i.e., datasets): What activities are in the dataset? We introduce a novel visualization that succinctly represents the totality of 100+ GB datasets by plotting the occurrence of provenance graph neighborhoods in a time series. How synthetic is the background activity? We perform autocorrelation analysis of provenance neighborhoods in the training split to identify process behaviors that occur at predictable intervals in the test split. Finally, How conspicuous is the malicious activity? We quantify the proportion of attack behaviors that are observed as benign neighborhoods in the training split as compared to previously-unseen attack neighborhoods. We then validate these questions by profiling the classification performance of state-of-the-art intrusion detection systems (R-CAID, FLASH, KAIROS, GNN) against a battery of public benchmark datasets (DARPA Transparent Computing and OpTC, ATLAS, ATLASv2). We demonstrate that synthetic background activities dramatically inflate True Negative Rates, while conspicuous malicious activities artificially boost True Positive Rates. Further, by explicitly controlling for these factors, we provide a more holistic picture of classifier performance. This work will elevate the dialogue surrounding threat detection datasets and will increase the rigor of threat detection experiments.