On June 22, 2017, WikiLeaks released a new cache of documents detailing four tools allegedly used by the CIA as part of its ongoing “Vault 7” campaign. The leaked tools are named “EzCheese,” “Brutal Kangaroo,” “Emotional Simian,” and “Shadow.” When used in combination, these tools can be used to attack systems that are air-gapped by using weaponized USB drives as an exfiltration channel. Per the documentation, deployment of the tool takes place by unwitting targets; however, the use of such tools could also easily be deployed purposefully by complicit insider actors.
Brutal Kangaroo is a suite of tools that can be used to attack air-gapped networks by using weaponized USB drives as a covert channel. For configuration, an attacker would have the ability to pick how the tool is delivered; the tool can be set to no configuration, EzCheese, “Lachesis” LinkFiles, or “RiverJack” LinkFiles. EzCheese, Lachesis, and RiverJack appear to be LNK exploits that can be used to gain access to a system with little to no user interaction. Brutal Kangaroo also has the ability to read configuration files and compress the data, making detection and analysis much more difficult.
EzCheese is an LNK exploit which can be used to exploit systems via USB drives. The payload can be configured to use an x86 or x64 DLL file, which can be executed simply by viewing the directory in Explorer. Per the documentation released by WikiLeaks, EzCheese was patched as of March 2015; analysis suggests that EzCheese is the LNK exploit patched in CVE-2015-0096. Open Source analysis of Microsoft patches issued during this period identify two exploits using LNK files, CVE-2010-2568 (MS10-046) and CVE-2015-0096. CVE-2015-0096 is particularly interesting, as this exploit uses the same flaw as MS10-046, which was not fully patched by Microsoft. MS10-046 was made public with the analysis of “Stuxnet,” and was an LNK exploit identified inside of the binary file. Stuxnet was used to attack air-gapped networks with weaponized USB drives, suggesting an overlap of tactics, techniques, and procedures (TTPs).
Lachesis (Okabi Links)
Lachesis can be deployed using autorun.inf on a USB drive when a drive is inserted into a machine, and can also be configured with an x86 or x64 DLL’s for code execution. This works for Windows 7 systems, and the CVE for this exploit is currently unknown.
RiverJack (Okabi Links)
RiverJack is another technique for launching exploits via USB. To launch, RiverJack uses the library-ms functionality to gain execution. Per the documentation, LNK files can be set to hidden and it is not necessary to view these files for deployment. This exploit works against Windows 7, 8, and 8.1; the current CVEs surrounding this technique are currently unknown.
Emotional Simian is a data collections tool that can be used to gather files from infected systems and store them on USB drives. This tool can be configured to find files based on certain patterns, such as by filenames or extensions. File collection can occur on target systems based on modified and accessed dates in order to not collect duplicate files. Emotional Simian can also be configured to remove itself from an infected machine based on the date of the system; by default, it is set to remove itself after two years.
While this can be deployed by witting participants and insiders, the main deployment method is intended to be covert via unwitting hosts. In order to compromise the air-gapped systems, attackers will infect systems to which they have access, which are known as the “primary host.” Once a USB drive from this host has been compromised, it can be plugged into an air-gapped system where data collection begins; the data can then be saved to a separate partition on the USB drive. Once data is collected and the USB is plugged back into the primary host, other tools can be used to siphon the data off of the system. The data is then later processed.
Once the USB tools have been deployed inside of a network, Shadow can be used to set up covert channels which can be used to send files back and forth. Similar to Emotional Simian, Shadow can be configured to collect certain files based on filename patterns and modified times. USB drives can be configured to be converted into Shadow drives, which allocate 10 percent of a USB drive partition for moving files. Infected systems can receive packet broadcasts with instructions and collected files can be assembled for post-processing. If pieces are missing, the tool will label chunks as missing; these missing pieces of data can be collected and reassembled later.
While the tools described are used primarily by nation-state actors for covert data collections against unwitting victims, the tools could be used by a malicious insider for covertly collecting files. Flashpoint assesses with moderate confidence that the March 2015 patching of LNK exploit CVE-2015-0096 is likely EzCheese, which was an extension of patch MS10-046. MS10-046 was exploited by Stuxnet to attack air-gapped networks via USB drives, which is a significantly overlapping tactic, technique, and procedure (TTP) between Stuxnet and Brutal Kangaroo. LNK exploits are dangerous as they require little to no user interaction, and infection can occur simply by having the file rendered on the system.
Nine days prior to the release of the new Vault 7 dump, Microsoft patched CVE-2017-8464, which was described as a remote code execution vulnerability using LNK exploits; this exploit was rated as critical and in the wild. In the patch notice, Microsoft mentioned that the code could be used and deployed to removable drives to infect hosts. Microsoft did not provide the source of where the information on the vulnerability came from; it is currently unknown if CVE-2017-8464 fixes the LNK exploits described above.
For mitigations, Flashpoint recommends monitoring USB drive use because it is the primary deployment vector for these tools. LNK files should not typically be on USB drives; their presence may serve as an early warning of potentially suspicious activities.