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Zero-Day Exploit Used for DUQU

We have been closely monitoring developments on the DUQU malware since our initial blog post when the threat broke the news. And just recently, the Hungary-based security laboratory that initially reported about DUQU released more information that sheds more light into the nature of the said threat.

Their report indicates that a Microsoft Word document that triggers a zero-day kernel exploit was identified as the dropper for DUQU. Upon successful exploitation, the Microsoft Word file drops the installer files that load the DUQU components that were initially reported a couple of weeks back.

The installer files are composed of a .SYS file detected as RTKT_DUQU.B, and a .DLL file detected as TROJ_DUQU.B. RTKT_DUQU.B loads TROJ_DUQU.B into the system. TROJ_DUQU.B, on the other hand, drops and decrypts the DUQU components, RTKT_DUQU.A, TROJ_DUQU.ENC, and TROJ_DUQU.CFG. Below is a simple behavior diagram of the threat.

Details regarding the zero-day exploit used have not yet been disclosed. However, Microsoft is expected to release information on it soon. As a member of the Microsoft Active Protections Program (MAPP), if Microsoft provides information on ways we can protect customers while a security patch is being developed, we will add these protections to our products as quickly as possible and update you with that information.

This new information allows us to have more educated theories of how the DUQU attack took place. Considering the usage of a Microsoft Word document, it is likely that this was initially deployed through email messages sent to employees in the targeted organization.This further verifies our earlier hypothesis that DUQU is part of a highly targeted attack aimed at exfiltrating information from targeted entities. For more information on DUQU and the nature of highly targeted attacks, please check the following reports:
We have created the proactive detections of TROJ_DUQUCFG.SME and RTKT_DUQU.SME to address future variants of DUQU component files. Also, the Threat Discovery Appliance (TDA) protects enterprise networks by detecting network activity and the malwares’ connection to the C&C server through the rules 473 TCP_MALICIOUS_IP_CONN, 528 HTTP_Request_DUQU, and 529 HTTP_Request_DUQU2.

Update as of November 3, 2011, 8:30 PM PST

Microsoft released a security advisory regarding the vulnerability used by DUQU.
The vulnerability exists in the Win32k TrueType font parsing engine and allows elevation of privilege. According to the advisory, a successful exploitation can allow an attacker to run arbitrary code in kernel mode.
We are currently collecting more information about this, and will update this blog entry with our findings as soon as possible.

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