Researchers have developed a proof-of-concept attack that uses steganography to establish highly covert malware command and control channels on the Instagram social media network.
In researching a way to demonstrate the PoC, the researchers at security firm Endgame also stumbled upon a separate weakness in Apple’s Mac OS X that would expose some users running version 10.11.5-6 of the operating system to malicious attacks just by viewing Instagram images on their computer.
Apple has been informed of the issue and a fix for the problem is supposed to have been included in the Sierra version of the operating system, Endgame said.
Steganography is a term that is used to describe the process of concealing images and text in plain sight by inserting it into another seemingly innocuous image or block of text. The tactic has been used years, in the digital context, to hide secret information without triggering any of the attention associated with other methods of concealment, like cryptography.
Previously, threat actors have used steganography for concealing command and control code. And a growing number of attackers have begun using social media sites to establish C&C channels for remotely controlling compromised computers.
Botmasters, for instance, have begun increasingly using networks like Twitter as their command and control infrastructures because of how difficult it is for defenders to distinguish C&C traffic from normal social networking traffic.
Endgame's PoC attack, dubbed Instegogram, is believed to be the first to show how code hidden in images posted on social media sites can be used for command and control.
“The PoC was intended to demonstrate that relatively simple image steganography can be used for malware C2 on social media sites,” says Amanda Rousseau, a malware researcher at Endgame. “Image stego for C2 isn’t new, and social media for C2 isn’t new, but we believe we’re the first to demonstrate that both can be used together for extremely stealthy C2.”
For the Instegogram PoC, Endgame researchers demonstrated how to hide C&C messages in digital images posted to Instagram.
The research, which was presented at the DEF CON Crypto Village earlier this year, showed how an attacker could insert C&C code into images in a manner as to survive any image re-encoding, compression, resizing, or other transformation that Instagram might automatically make to uploaded images.
The Endgame researchers then showed how a remote access Trojan could be configured to communicate with specific Instagram accounts under their control and containing images laced with C&C code.
“The malware includes a steganographic decoder that extracts a payload from each downloaded image, allowing arbitrary command execution on the remote system,” Endgame said in its description of the PoC.
The malware code was built on Mac OSX as an uncertified MacOS app. In order to execute the PoC, the researchers needed to bypass Apple’s Gatekeeper tool for blocking unsigned apps from running on a system. They found one Gatekeeper bypass flaw that exposed some Mac OS users to malware of the sort being demonstrated in the PoC.
Users running OS X version 10.11.5-6 and Microsoft Excel 2016 version 15.24 are vulnerable to the threat if they allow Microsoft Office macros to execute, and have access to Instagram, Rousseau says.
"Apple has been very responsive,” she says. “We worked with their team directly to notify them of this issue prior to the talk and they told us that they would be fixing the issue in Sierra. We haven’t confirmed whether this is the case.”