Duqu exploits zero-day Windows kernel vulnerability to infect computers

Security researchers from the CrySyS laboratory in Hungary have located an installer for Duqu, the Stuxnet-inspired threat that has kept the security industry on its toes for the past couple of weeks, and determined that it exploits a previously unknown vulnerability in the Windows kernel.

The Laboratory of Cryptography and System Security (CrySyS) from the Budapest University of Technology and Economics was also the first to identify Duqu's other components, like the malicious driver and DLL that dropped on infected systems.

"Our lab [...] pursued the analysis of the Duqu malware and as a result of our investigation, we identified a dropper file with an MS 0-day kernel exploit inside," the CrySyS researchers announced.

"We immediately provided competent organizations with the necessary information such that they can take appropriate steps for the protection of the users," they added.

According to Symantec, whose experts analyzed the samples provided by CrySyS, Duqu infects computers via a Microsoft Word document (.doc) that exploits a zero-day Windows vulnerability when opened.

The rogue document most likely reaches targeted organizations as part of a social engineering attack against their employees. "The Word document was crafted in such a way as to definitively target the intended receiving organization," the Symantec researchers pointed out.

Microsoft has been alerted about the vulnerability and is working on a fix. In the meantime, users should follow best practices and not open documents from unknown sources.

Because this is a kernel vulnerability and only a single installer was discovered so far, the researchers do not exclude other infection vectors, aside from maliciously crafted .doc files.

Symantec's researchers have also made other interesting discoveries related to the threat. These include the fact that Duqu is capable of infecting computers that are not connected to the Internet by copying itself to folders shared on the network.

It turns out that the malware has a fallback mechanism that kicks in when it cannot detect an active Internet connection, involving downloading updated configuration files from other infected systems on the same network.

"Duqu creates a bridge between the network's internal servers and the C&C [command and control] server. This allowed the attackers to access Duqu infections in secure zones with the help of computers outside the secure zone being used as proxies," the security researchers explained.

Another important find is a new command and control server hosted in Belgium. This is the first Duqu C&C server identified after the original one in India was shut down, confirming suspicions that whoever is behind this malware is monitoring the situation and acting in response.

So far, Symantec was able to confirm infections in France, Netherlands, Switzerland, Ukraine, India, Iran, Sudan and Vietnam, while other vendors have reported incidents in Austria, Hungary, Indonesia and the United Kingdom. This is a clear indication that Duqu operates on a global scale.