'ObliqueRAT' Now Hides Behind Images on Compromised Websites

In the latest example of threat actors quickly shifting gears when their methods are discovered and exposed publicly, the operator of the remote access Trojan ObliqueRAT has now changed its infection tactics.

Researchers from Cisco Talos recently discovered that the so-called Transparent Tribe attack group behind ObliqueRAT is using malicious Microsoft Office documents to point users to compromised websites hosting its malicious payload. In previous campaigns, the attackers had used the weaponized Office documents to drop ObliqueRAT directly onto the victim's system. But now it's hiding the malware in seemingly benign image files on compromised websites, and using the poisoned Office documents merely to direct victims to the payload.

Steganography, hiding malicious code inside an image, is not new. But Cisco Talos threat researcher Asheer Malhotra says this technique of using malicious documents to point users to payloads in image files isn't very common. "The fact that this threat actor is now using this technique—that they've never used before—is interesting," Malhotra says. "This shows that the actors are constantly designing new infection techniques and evolving their capabilities with a focus on stealth."

ObliqueRAT is a Trojan that has been associated with campaigns targeting organizations in South Asia. The malware is equipped to primarily spy on users, including via the system webcam. It can take screenshots, steal files, and gives attackers the ability to deliver malicious content and execute arbitrary commands on compromised systems. Proofpoint, Kaspersky, and others that also have been tracking the group say Transparent Tribe is a highly active APT that has been operational since at least 2013 and mainly targeting Indian military targets and diplomatic offices including those based in Saudi Arabia and Kazakhstan.

Malhotra says that Cisco Talos researchers have been unable to determine exactly how the attackers are delivering the malicious Microsoft Office documents to victims. One possibility is that they are distributing it via an email-based infection vector, which is how a majority of malware is delivered these days. Another possibility is that the attacker is using URLs to deliver the malicious documents rather than email attachments.

Once the malicious document is on a system, the attackers simply need to trick the victim into opening the document. A malicious macro within the document is trigged when the document is closed. "The macro will fetch and decode the malicious ObliqueRAT payload from a compromised website," Malhotra says. "ObliqueRAT is then executed on the targeted endpoint using a malicious shortcut created by the macro in the currently logged-in user's Startup directory."

Malhotra says Cisco Talos also is unsure about the methods the attackers might be using to compromise websites and to plant a poisoned image file with the ObliqueRAT payload. Potential infection vectors could include everything from easily guessed weak credentials to known exploits hitting outdated and unpatched hosting platforms.

Just this week, Sophos reported on another threat actor likely using similar techniques to breach vulnerable websites and inject content. The attackers trick search engines into treating the infected site as a trustworthy source; in that campaign, too, the threat actor has been constantly evolving the malware and the malware distribution technique to try and stay one step ahead of defenders.