The Dell SecureWorks Counter Threat UnitSM (CTU) research team has been analyzing an emerging malware threat identified as the Duqu trojan. This Trojan horse has received a great deal of attention because it is similar to the infamous Stuxnet worm of 2010. This report includes answers to questions about this threat. CTU researchers have put countermeasures in place to detect Duqu C2 traffic, and they continue to monitor for new Duqu samples and update protections as needed.
The Duqu trojan is composed of several malicious files that work together for a malicious purpose. The first component is a Windows kernel driver that searches for and loads encrypted dynamic link library (DLL) files. The decrypted DLL files implement the main payload of Duqu, which is a remote access trojan (RAT). The RAT allows an adversary to gather information from a compromised computer and to download and run additional programs.
In addition to the RAT, another piece of malware was recovered with Duqu in one instance. This malware is an information stealer designed to log user keystrokes and other information about the infected system. This piece of malware is believed to be related due to programming similarities with the main Duqu executables.
There has been much speculation that Duqu is a new version of Stuxnet or that it was written by the same authors. There are several factors that could influence these speculations:
|Infection Methods||Unknown||USB (Universal Serial Bus)|
PDF (Portable Document Format)
|Dropper Characteristics||Installs signed kernel drivers
to decrypt and load DLL files
|Installs signed kernel drivers |
to decrypt and load DLL files
|Zero-days used||None yet identified||Four|
|Command and Control||HTTP, HTTPS, Custom||HTTP|
|Self propagation||None yet identified||P2P (Peer to Peer) using RPCs |
(Remote Procedure Call)
WinCC Databases (Siemens)
|Data exfiltration||Add-on, keystroke logger for
user and system info stealing
|Built-in, used for versioning |
and updates of the malware
|Date triggers to infect or exit||Uninstalls self after 36 days||Hard coded, must be in the following range: |
19790509 => 20120624
|Interaction with control systems||None||Highly sophisticated interaction |
with Siemens SCADA control systems
Both Duqu and Stuxnet are highly complex programs with multiple components. All of the similarities from a software point of view are in the "injection" component implemented by the kernel driver. The ultimate payloads of Duqu and Stuxnet are significantly different and unrelated. One could speculate the injection components share a common source, but supporting evidence is circumstantial at best and insufficient to confirm a direct relationship. The facts observed through software analysis are inconclusive at publication time in terms of proving a direct relationship between Duqu and Stuxnet at any other level.
Unlike Stuxnet, Duqu does not contain specific code that pertains to supervisory control and data acquisition (SCADA) components such as programmable logic controllers (PLCs). Duqu's primary purpose is to provide an attacker with remote access to a compromised computer, including the ability to run arbitrary programs. It can theoretically be used to target any organization.
Duqu facilitates an adversary's ability to gather intelligence from an infected computer and the network. CTU malware analysts have not identified any specific market segments, technologies, organizations or countries that are targeted by the Duqu malware.
The Duqu trojan attempts to use the network to communicate with a remote command and control (C2) server to receive instructions and to exfiltrate data. Analysis of Duqu revealed that it uses the 220.127.116.11 IP address as its C2 server. This IP address is located in India and has been shut down by the hosting provider. Also, Duqu may attempt to resolve the kasperskychk.dyndns.org domain name. The resulting IP address is not used for communications, so this lookup may serve as a simple Internet connectivity check. Administrators should monitor their network for systems attempting to resolve this domain or connect to the C2 IP address for possible infection.
Duqu uses multiple protocols to communicate with its C2 server, including standard HTTP on TCP port 80 and a custom protocol on TCP port 443. Some of Duqu's communications that use TCP port 443 do not use the HTTPS protocol. Organizations may be able to monitor egress traffic through proxy servers or web gateways and investigate network traffic that does not conform to the SSL (Secure Sockets Layer) specification. Non-SSL traffic on port 443 is commonly observed with other threats, and this behavior is not exclusive to Duqu.
The CTU research team is aware of the following files that may be installed by the Duqu trojan. The byproducts in Table 2 have been collected from multiple Duqu variants and would not be present on a single infected computer.
(sometimes referred to as keylogger.exe)
The name "Duqu" was assigned to this malware because the keylogger program creates temporary files that begin with the prefix "~DQ". A computer infected with Duqu may have files beginning with "~DQ" in Windows temporary directories.
The mechanism by which Duqu infections occur is unknown. Current analysis of Duqu has not revealed any ability to infect additional systems like the Stuxnet worm could. In addition, all of the Duqu files CTU researchers have analyzed would likely have been installed by an initial installer or "dropper" malware. None of the original installers have been recovered. The recovery of one of these installers may help provide clues to how Duqu infections occurred.
Dell SecureWorks does not identify individual tools as APT. APT is a threat actor or actors targeting an organization for assets of interest. An APT involves planning by the adversary, teams with specialized roles, multiple tools, patience and persistence. While Duqu does provide capabilities used by other tools observed in APT-related intrusions, an assessment of the particular threat requires knowledge of the adversary, targeted organization and assets and the scope of attacks.
Since its discovery, security vendors have worked to improve their ability to detect Duqu. However, the author may simply release newer variants that are no longer detected by antivirus and antimalware products.
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