Malware hides C&C server communications using Google Docs function

Pierluigi Paganini November 21, 2012

The ways explored by malware creators are unlimited, recently Symantec has announced the discovery of a new operational mode for backdoor trojan Makadocs, the security firm has in fact reported that a variant of malware hides its command-and-control (C&C) server communications using a legitimate Google Docs function.

Backdoor.Makadocs is a Trojan horse that opens a backdoor on the victims attempting to steal information.
Google Docs is a free, Web-based office suite and data storage service offered by Google within its Google Drive service that allows to create and edit documents online while collaborating in real-time with other users. Symantec discovered an unusual fruition of Google Docs which provides for its use as a proxy server for the malware, the malicious application use the popular service as intermediary step to route information to C&C servers.

The backdoor appears seems to be able to compromise machines running last versions of Microsoft OSs such as Windows Server 2012 and the latest Windows 8.

At the moment only few instances of the malware have been detected world wide, around a hundred locates in south America, to be exact in Brazil, and this aspect let experts to speculate that the authors have chosen a specific region to conduct some tests.

The infection vector is a malicious Word or Rich Text Format (RTF) documents that the victims open inadvertently, as usual the file is sent via a phishing email.

Kevin Haley, director of Symantec Security Response, explained the thanks a feature in Google Docs called “viewer” it is possible to access to a document locates on another user’s machine. Pointing the malicious file with the function it is possible to infect the victims. Makadocs backdoors is able to use the legitimate function Google Docs “viewer” to access its C&C server.

Haley declared to SC magazine:

“There’s a feature in Google Docs called “viewer” that allows you to look at a document on another person’s machine,” “You can get the URL of where the document is [through the feature].”

The new techniques adopted by the authors of malware allows to avoid common controls on communications directed to C&C servers.

Acting in this way malware avoid direct connection to the C&C, and a further element of complication is that connection to the Google Docs server is encrypted using HTTPS making it difficult to be blocked. The Makadocs backdoor doesn’t exploit any particular vulnerability and hasn’t been created specifically for Windows 8 according the statements of the official Symantec post.

“However, this malware does not use any particular function unique to Windows 8 and we know that this malware existed before the launch of Windows 8. Based on these facts, we believe this code must be an update to the malware.”

To arrest malware diffusion Google will have to adopt necessary countermeasures filtering incoming traffic to its services that violates Google product policies. Official sources released the following declaration to SCmagazine

“We investigate and take action when we become aware of abuse.”

The discovery raises a couple of reflections:

  • The authors of malware are exploring new channels to avoid common defense systems, through the exploitation of new vulnerabilities and developing new evasion techniques to make difficult the detection such as peer to peer protocols and Google Docs function. Which will be next one?
  • Who is behind the malware? Despite it appears really simple the techniques to elude the controls  is very original and could suggest that someone is preparing an agent for a new cyber espionage campaign. We must be prepared, the monitoring of event such this one is crucial, it could alert security community on ongoing activities.

Pierluigi Paganini

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