The experts suspect that it all started with a classic spear phishing attempt because one the “victims zero” they identified had its mailbox and web browser history wiped to avoid detection. Experts at Kaspersky confirmed that the infection stage was similar to the one implemented by Duqu that relied on malicious Word Documents containing an exploit for a zero-day vulnerability (CVE-2011-3402).
Duqu relied on an exploit that allowed the attackers to jump directly into Kernel mode from a Word Document, a technique considered by researchers very powerful and extremely rare.
Authors of Duqu 2.0 used a stolen certificate from the Foxconn company to implement a persistence mechanism and remain under the radar.
“The attackers created an unusual persistence module which they deploy on compromised networks. It serves a double function – it also supports a hidden C&C communication scheme. This organization-level persistence is achieved by a driver that is installed as a normal system service.”
“During their operations the Duqu threat actors install these malicious drivers on firewalls, gateways or any other servers that have direct Internet access on one side and corporate network access on the other side. By using them, they can achieve several goals at a time: access internal infrastructure from the Internet, avoid log records in corporate proxy servers and maintain a form of persistence after all,” continues the post.
The C&C mechanism relies on the usage of network pipes and mailslots, raw filtering of network traffic and masking C&C traffic inside image files. To connect the C&C servers, both 2011 and 2014/2015 versions of Duqu can hide the traffic as encrypted data appended to a harmless image file.
“It also doesn’t directly connect to a command-and-control server to receive instructions,” explained Kurt Baumgartner, principal security researcher at Kaspersky Lab. “Instead, the attackers infect network gateways and firewalls by installing malicious drivers that proxy all traffic from internal network to the attackers’ [command and control servers]. Combined, this made discovery very difficult.”
“Another interesting observation is that besides these Duqu drivers we haven’t uncovered any other malware signed with the same certificates,” the researchers continued. “That rules out the possibility that the certificates have been leaked and are being used by multiple groups.. which strengthens the theory they hacked the hardware manufacturers in order to get these certificates.”