A threat actor has used sophisticated Word documents to deliver Flash exploits in attacks aimed at NATO governments, reported Cisco’s Talos security intelligence and research group.
According to researchers, attackers have used specially designed documents to perform reconnaissance on infected systems and avoid sandboxes. Talos has compared this reconnaissance framework to the Russian Matryoshka nesting doll due to its complex workflow.
The attacks observed by Cisco were launched during the Christmas and New Year holidays. The Word document used as bait was titled “Statement by the NATO Secretary General following a meeting of the NATO-Russia Council,” which has led experts to believe that the targets were likely NATO member countries.
The text in the document has been copied from the official NATO website and the file itself does not contain any actual exploits, making it more difficult to detect.
The document, an RTF file, contains several embedded objects, including OLE and Adobe Flash objects, that are extracted in succession.
“The OLE object contains an Adobe Flash object. The purpose of the Adobe Flash is to extract a binary blob embedded in itself via ActionScript execution,” Talos researchers explained in a blog post. “This blob is a second encoded and compressed Adobe Flash object. The encoded algorithm is based on XOR and zlib compression. This is the second Adobe Flash in the final payload located within the document.”
In the first phase, ActionScript is used to send an HTTP request containing information about the infected system to the command and control (C&C) server. This information can allow the attacker to determine if the infected system is a virtual machine or a sandbox.
Two additional requests are made, each using data obtained from the response to the previous request. In the final phase, a Flash exploit is fetched, and loaded and executed on the fly.
DNS data from Cisco’s Umbrella system showed that numerous requests were made to the C&C domain starting with January 16. These requests came from the security research community, which has triggered a response from the attackers.
They replaced the malicious payload with junk data in order to create resource issues for some security products and disrupt investigation efforts.
“[The] actor realized security researchers were poking around their infrastructure and then rigged the infrastructure to create resource issues for some security devices,” experts said. “These are the characteristics of reasonably advanced attackers who have designed an efficient minimalist framework that was able to adapt purposes on the fly.”
While Cisco has not shared any information on who might be behind the attacks, NATO governments have often been targeted by Russia-linked threat actors, including the cyber espionage group known as Pawn Storm (aka APT28, Fancy Bear and Sofacy). Comparison of the reconnaissance framework to a Matryoshka doll also suggests Russian involvement.