  Modern attacks against enterprises often have multiple targets inside the
enterprise network. Due to the large size of these networks and increasingly
stealthy attacks, attacker activities spanning multiple hosts are extremely
difficult to correlate during a threat-hunting effort. In this paper, we
present a method for an efficient cross-host attack correlation across multiple
hosts. Unlike previous works, our approach does not require lateral movement
detection techniques or host-level modifications. Instead, our approach relies
on an observation that attackers have a few strategic mission objectives on
every host that they infiltrate, and there exist only a handful of techniques
for achieving those objectives. The central idea behind our approach involves
comparing (OS agnostic) activities on different hosts and correlating the hosts
that display the use of similar tactics, techniques, and procedures. We
implement our approach in a tool called Ostinato and successfully evaluate it
in threat hunting scenarios involving DARPA-led red team engagements spanning
500 hosts and in another multi-host attack scenario. Ostinato successfully
detected 21 additional compromised hosts, which the underlying host-based
detection system overlooked in activities spanning multiple days of the attack
campaign. Additionally, Ostinato successfully reduced alarms generated from the
underlying detection system by more than 90%, thus helping to mitigate the
threat alert fatigue problem
