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Malware Evades Detection By Counting Word Documents (threatpost.com)

Posted by EditorDavid on from the I-see-you-are-trying-to-evade-infection dept.

"Researchers have found a new strain of document-based macro malware that evades discovery by lying dormant when it detects a security researcher's test environment," reports Threatpost, The Kaspersky Lab security news service. Slashdot reader writes: Once a computer is compromised, the malware will count the number of Word documents stored on the local drive; if it's more than two, the malware executes. Otherwise, it figures it's landed in a virtual environment or is executing in a sandbox and stays dormant.

A typical test environment consists of a fresh Windows computer image loaded into a VM. The OS image usually lacks documents and other telltale signs of real world use [according to SentinelOne researcher Caleb Fenton]. If no Microsoft Word documents are found, the VBA macro's code execution terminates, shielding the malware from automated analysis and detection. Alternately, if more than two Word documents are found on the targeted system, the macro will download and install the malware payload.

7 of 70 comments (clear)

  1. Easy solution to avoid this malware... by Anonymous Coward · · Score: 4, Insightful

    Don't use Word.

    1. Re: Easy solution to avoid this malware... by Billly+Gates · · Score: 5, Insightful

      Even if you use LibreOffice I am sure you have word and excel documents lying around. If you do real work or a college student you are going to be emailed office documents.

      --
      http://saveie6.com/
    2. Re: Easy solution to avoid this malware... by sound+vision · · Score: 5, Insightful

      Have you taken a college course or had to deal in a "business-to-business" interaction at all in the past 15 years? They all use the MS Word document format. I took college courses from 2007-2012 at several campuses, of course with different professors... They pretty much all used Word documents to distribute whatever documents they needed to digitally. I think there was maybe 1 course where we were given a link to a PDF. It's not about what you use, it's about what the other guys use.

    3. Re: Easy solution to avoid this malware... by DMFNR · · Score: 4, Insightful

      How did you read that much in to just one sentence? I think what he meant is that the Office formats are so commonplace that even if you use different tools it's pretty likely that you're going to encounter .docx or xslx files. You can't control what software other people use and if you're in an office or educational environment it's almost a guarantee you will receive files in the Microsoft formats, in fact, isn't that one of the big selling points for LibreOffice? Its compatibility with those tools? I've even seen free software with .docx files available in the doc/ folder of their source packages! It has nothing to do with whether or not your choice of software is capable of "real work" or whatever the hell you're talking about, it's just that it's really hard to avoid Microsoft format stuff when you work with other people.

      Your point still stands that there are plenty of ways to deal with these files without having Office installed. That's the key here, it's not that the files are particularly dangerous, it's the interpreter that runs the macros you have to worry about! Plenty of solutions to deal with these formats available without having Office installed, Office 365 as you mentioned, Libre Office, Google Docs. MS software is like heroin, it feels pretty good when it's doing what its supposed to, but when everything goes wrong you're going to get hurt bad.

  2. Re:I have a out of this world solution by Opportunist · · Score: 4, Insightful

    Brilliant. Pure genius. Nobody ever could come up with this idea.

    No, but seriously. The point is that this thwarts automatic detection tools. Of course, if a human is examining the malware, he will dissect it and analyze it and quickly realize that it counts documents. The automated tool will only notice that it does ... well, nothing.

    --
    We used to have a Bill of Rights. Now, with the rights gone, all we have left is the bill.
  3. Re:I have a out of this world solution by sound+vision · · Score: 4, Insightful

    This piece of malware looked for Word documents, but the next one won't. Maybe it looks for image files, or it looks to see if the web browser has a significant cache built up. Or something more subtle than that. A better idea would be to create system images of used systems, periodically swapping them out, to make it a moving target.

  4. Counting documents is doing something by Anonymous Coward · · Score: 2, Insightful

    Am I retarded? It doesn't matter.

    Counting documents is "doing something" If the automated system doesn't see the macro accessing the filesystem and doing searches on the filesystem, then the automated system is more retarded than me.