Friday, March 20, 2009

SRI International: Analysis of Conficker C

This addendum provides an evolving snapshot of our understanding of the latest Conficker variant, referred to as Conficker C. The variant was brought to the attention of the Conficker Working Group when one member reported that a compromised Conficker B honeypot was updated with a new dynamically linked library (DLL). Although a network trace for this infection is not available, we suspect that this DLL may have propagated via Conficker's Internet rendezvous point mechanism (Global Network Impact). The infection was found on the morning of Friday, 6 March 2009 (PST), and it was later reported that other working group members had received other DLL reinfections throughout the same day. Since that point, multiple members have reported upgrades of previously infected machines to this latest variant via HTTP-based Internet rendezvous points. We believe this latest outbreak of Conficker variant C began first spreading at roughly 6 p.m. PST, 5 March 2009.

In this addendum report, we summarize the inner workings and practical implications of this latest malicious software application produced by the Conficker developers. In addition to the dual layers of packing and encryption used to protect A and B from reverse engineering, this latest variant also cloaks its newest code segments, along with its latest functionality, under a significant layer of code obfuscation to further hinder binary analysis. Nevertheless, with a careful mixture of static and dynamic analysis, we attempt here to summarize the internal logic of Conficker C.

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