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Security researchers brought to life and released a wicked variant of Clippy, the recently resurfaced assistant in Microsoft Office that we all loved so much to hate, that makes it more difficult to detect a malicious macro in documents. Dubbed Evil Clippy, the tool modifies Office documents at file format level to spew out malicious versions that get by the static analysis of antivirus engines and even utilities for manual inspection of macro scripts. To do this, it takes advantage of undocumented features, unclear specifications, and deviations from intended implementations. Macros are snippets of VBA (Visual Basic for Applications) code that automate tasks in Microsoft Office applications. They are constantly used to deliver malware when the user opens a document. Researchers at Dutch security testing company Outflank developed Evil Clippy for professionals running red team attacks against a client organization. The tool runs on Windows, macOS, and Linux. The tool can be used with documents formats for Microsoft Office 97 - 2003 (.DOC and .XLS), and  2007 and above (.DOCM and .XLSM, which are basically ZIP containers and come with macros enabled). All these file types use the Compound File Binary Format (CFBF) and Outflank's program modifies it using the OpenMCDF library. One technique Evil Clippy uses to generate a maldoc is "VBA stomping," a method detailed by Walmart's security team, by which the original code of the VBA script can be replaced by a compiled version for the VBA engine called pseudo-code, or p-code in short. Infosec expert Vesselin Bontchev detailed publicly that VBA scripts can execute at runtime in three forms, with p-code being the most popular. We more posted on OUR FORUM.

 

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