Today, June 22nd 2017, WikiLeaks publishes documents from the Brutal Kangaroo project of the CIA. Brutal Kangaroo is a tool suite for Microsoft Windows that targets closed networks by air gap jumping using thumbdrives. Brutal Kangaroo components create a custom covert network within the target closed network and providing functionality for executing surveys, directory listings, and arbitrary executables.
The documents describe how a CIA operation can infiltrate a closed network (or a single air-gapped computer) within an organization or enterprise without direct access. It first infects a Internet-connected computer within the organization (referred to as "primary host") and installs the BrutalKangaroo malware on it. When a user is using the primary host and inserts a USB stick into it, the thumbdrive itself is infected with a separate malware. If this thumbdrive is used to copy data between the closed network and the LAN/WAN, the user will sooner or later plug the USB disk into a computer on the closed network. By browsing the USB drive with Windows Explorer on such a protected computer, it also gets infected with exfiltration/survey malware. If multiple computers on the closed network are under CIA control, they form a covert network to coordinate tasks and data exchange. Although not explicitly stated in the documents, this method of compromising closed networks is very similar to how Stuxnet worked.
The Brutal Kangaroo project consists of the following components: Drifting Deadline is the thumbdrive infection tool, Shattered Assurance is a server tool that handles automated infection of thumbdrives (as the primary mode of propagation for the Brutal Kangaroo suite), Broken Promise is the Brutal Kangaroo postprocessor (to evaluate collected information) and Shadow is the primary persistence mechanism (a stage 2 tool that is distributed across a closed network and acts as a covert command-and-control network; once multiple Shadow instances are installed and share drives, tasking and payloads can be sent back-and-forth).
The primary execution vector used by infected thumbdrives is a vulnerability in the Microsoft Windows operating system that can be exploited by hand-crafted link files that load and execute programs (DLLs) without user interaction. Older versions of the tool suite used a mechanism called EZCheese that was a 0-day exploit until March 2015; newer versions seem use a similar, but yet unknown link file vulnerability (Lachesis/RiverJack) related to the library-ms functionality of the operating system.