Cloud Threats Memo: Preventing the Exploitation of Dropbox as a Command and Control

IndigoZebra is a Chinese state-sponsored actor mentioned for the first time by Kaspersky in its APT Trends report Q2 2017, targeting, at the time of its discovery, former Soviet Republics with multiple malware strains including Meterpreter, Poison Ivy, xDown, and a previously unknown backdoor called “xCaon.”

Now, security researchers from Check Point have discovered a new campaign by Indigo Zebra, targeting the Afghan National Security Council via a new version of the xCaon backdoor, dubbed BoxCaon, and characterized by the exploitation of an attacker-controlled Dropbox account to receive commands and exfiltrate data.

This is not the first example of Dropbox being abused for command and control, recent examples include DropBook, a backdoor used by the Molerats (aka The Gaza Cybergang) in a cyber espionage campaign against targets in the Middle East (interestingly the same campaign also used Facebook and Google Docs for the same purpose), and DRBControl, an APT actor targeting gambling companies in Southeast Asia unearthed at the beginning of 2020.

Dropbox provides an ideal infrastructure for hosting a command and control or a drop zone: not only is its traffic considered trusted (and legacy technologies cannot differentiate a corporate instance from a personal one or a rogue one abused by attackers), but the application itself provides a flexible set of APIs that can be easily weaponized by the attackers. Something that Netskope has proven with the release of SaaSy_boi, a proof-of-concept that explores how the cloud provides redundancy and resilience for all applications.

How Netskope can detect rogue cloud instances used to host a command and control

Dropbox is one of thousands of services where Netskope can provide granular access control and one of the dozens for which instance detection is also available. In similar cases where it is exploited to host the command and control, it is possible to configure a policy that prevents potentially dangerous activities (such as upload and download) from non-corporate instances. It is possible to make the scope of the policy broader, blocking these activities for any unneeded cloud storage service that can potentially be exploited for command and control or malware distribution.

Stay safe!