## 1 Introduction  
Cyber attacks are constantly evolving in both sophistication and scale, reaching such an extent that the World Economic Forum considers it the second most threatening risk for global commerce over the next decade [1]. The underground economy that has been created has become so huge to the point of being comparable to the size of national economies. Contrary to most cyberattacks which have a 'hit-and-run' modus operandi, we have advanced persistent threats, most widely known through the abbreviation APT. In most cyber attacks, the threat actor would try to exploit a single exploit or mechanism to compromise as many hosts as possible and try to immediately monteize the abuse of the stored information and resources as soon as possible. However, in APT attacks, the threat actor opts to keep a low profile, exploiting more complex intrusion methods through various attack vectors and prolong the control of the compromised hosts. Indeed, this control may span several years, as numerous such incidents have shown. Due to their nature and impact, these attacks have received a lot of research focus as the heterogeneity of the attack vectors introduces many issues for traditional security mechanisms. For instance, due to their stealth character, APTs bypass antiviruses; therefore, more advanced methods are needed to detect them in a timely manner. Endpoint Detection and Response (EDR) systems provide a more holistic approach to the security of an organization as beyond signatures, EDRs correlate information and events across multiple hosts of an organization. Therefore, individual events from endpoints that could fall below the radar are collected, processed, and correlated, providing blue teams with a deep insight into the threats that an organization's perimeter is exposed to. Despite the research efforts and the advanced security mechanisms deployed through EDRs, recent events illustrate that we are far from being considered safe from such attacks. Since APT attacks are not that common and not all details can be publicly shared, we argue that a sanity check to assess the preparedness of such security mechanisms against such attacks is deemed necessary. Therefore, we decided to conduct an APT group simulation to test the enterprise defenses' capabilities and especially EDRs. To this end, we opted to simulate an APT attack in a controlled environment using a set of scripted attacks which match the typical modus operandi of these attacks. Thus, we try to infiltrate an organization using spear-phishing and malware delivery techniques and then examine the IOCs and responses produced by the EDRs. We have created four such use case scenarios which are rather indicative and diverse enough to illustrate the weak points of several perimeter security mechanisms, and more precisely EDRs. Based on the above, the contribution of our work is dual. First, we illustrate that, despite the advances in static and dynamic analysis, as well as multiple log collection mechanisms that are applied by state-of-the-art EDRs, there are multiple ways that a threat actor may launch a successful attack without raising suspicions. As it will be discussed, while some of the EDRs may log fragments of the attacks, this does not imply that these logs will trigger an alert. Moreover, even if an alert is triggered, one has to consider it from the security operations center (SOC) perspective. Practically, an SOC receives multiple alerts and each one with different severity. These alerts are prioritized and investigated according to this severity. Therefore, low severity alerts may slip below the radar and not be investigated, especially once the amount of alerts in an SOC is high [2]. Furthermore, we discuss how telemetry providers of EDRs can be tampered with, allowing an adversary to hide her attack and trails. To the best of our knowledge, there is no empirical assessment of the efficacy of real-world EDRs in scientific literature, nor conducted in a systematic way to highlight their underlying issues in a unified way.