The minds behind Duqu 2.0 used a stolen certificate in their attacks as part of a bid to stay stealthy, according to Kaspersky Lab.
The attackers used a valid digital signature from Hon Hai Precision Industry Co. LTD (also known as Foxconn Technology Group). Foxconn manufactures electronics for a wide range of companies, including Apple and BlackBerry.
The malware has been linked by security researchers to attacks on a number of targets, including venues tied to events and talks related to negotiations regarding Iran’s nuclear program as well as Kaspersky Lab itself, which discovered Duqu 2.0 on its own internal systems earlier this year.
According to Kaspersky Lab, the certificate was issued by VeriSign and used to sign a driver designed to mask command-and-control traffic.
“The attackers created an unusual persistence module which they deploy on compromised networks,” Kaspersky Lab’s Global Research & Analysis Team (GReAT) explained in a blog post. “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. On 64-bit systems, this implies a strict requirement for an Authenticode digital signature. We have seen two such persistence drivers deployed in the course of attacks.”
According to researchers at Kaspersky Lab, the attackers installed these malicious drivers on firewalls, gateways and servers with direct Internet access on one side and corporate network access on the other side. By using those drivers, the attackers can access internal infrastructure from the Internet, dodge log records in corporate proxy servers and maintain a form of persistence.
“In essence, the drivers are redirecting network streams to and from the gateway machine that runs it,” the researchers explained. “To forward connections, the attacker first has to pass a network-based “knocking” mechanism by using a secret keyword. We have seen two different secret keywords in the samples we collected so far: “romanian.antihacker” and “ugly.gorilla”.”
In the case of Duqu, the attackers have been careful not to use the same signature more than once, the researchers noted.
“During our previous research into Stuxnet and Duqu we have observed digitally signed malware (using malicious Jmicron and Realtek certs),” according to Kaspersky Lab. “Stealing digital certificates and signing malware on behalf of legitimate businesses seems to be a regular trick from the Duqu attackers. We have no confirmation that any of these vendors have been compromised but our indicators definitely show that the Duqu attackers have a major interest in hardware manufacturers such as Foxconn, Realtek and Jmicron. This was confirmed in the 2014/2015 attacks, when we observed infections associated with hardware manufacturers from APAC, including ICS and SCADA computer equipment manufacturers.”
“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. It also seems to indicate the Duqu attackers are the only ones who have access to these certificates, which strengthens the theory they hacked the hardware manufacturers in order to get these certificates.”